Osmotic adjustment is a prime drought stress adaptive engine in support of plant production

Improving soybean drought tolerance via silicon-induced changes in growth, physiological, biochemical, and root characteristics

Drought-induced osmotic stress is a significant constraint to soybean growth and yield, necessitating the development of effective mitigation strategies. Silicon acts as an important strategy to mitigate the negative stress effects of drought stress. The study was aimed to evaluate the potential of soil-applied silicon in alleviating drought stress in soybean. Two field capacities were tested: control (85% FC) and drought (50% FC), with four silicon application rates (0, 100, 200, and 300 kg ha-1) applied at sowing. Drought stress significantly affected the morphological parameters in soybean as plant height, leaf area, and water potential were reduced by 25%, 20%, and 36%, respectively, while root length increased as compared to control-85% FC. However, drought stress reduced root density, surface area, and biomass as compared to control-85% FC. Additionally, drought reduced photosynthetic rates, chlorophyll a and b levels, and stomatal conductance, while increasing malondialdehyde and hydrogen peroxide. The natural plant defense system was upregulated, with increased activity of phenolics, soluble proteins, and antioxidant enzymes like catalase, superoxide dismutase, and peroxidase. However, silicon applications, especially at 200 kg ha-1, significantly alleviated the negative effects of drought stress by improving morphophysiological and biochemical traits in soybeans. Compared to the control, Si200 increased plant height, root length, photosynthetic rate, and water potential by 22%, 39%, 23%, and 17%, respectively, as compared to control. Furthermore, silicon reduced malondialdehyde and hydrogen peroxide levels by 21% and 10%, enhancing plant resilience. Silicon supplementation also boosted biochemical attributes, with total soluble proteins, phenolics, and antioxidant enzyme activities increasing by 30%, 55%, 19%, 24%, and 31%, respectively, under drought conditions. In crux, silicon at 200 kg ha-1 effectively mitigated the effects of drought stress in soybean, becoming a more sustainable approach to sustain crop yield and food security.

Revealing drought tolerance strategies in pistachio clonal hybrids: role of osmotic adjustment

BACKGROUND

Pistachio (Pistacia vera L.) growth, yield and quality are affected by abiotic stress especially drought. Understanding the strategies that improve dehydration tolerance is essential for developing resistant pistachio rootstocks. In the experiment, nine-month-old saplings of seven clonal interspecies hybrids of Pistacia atlantica × P. integerrima (C1, C2, C16-1, C8-3, C4-2, C9-4 and UCB1) were assessed for growth and physiological responses to water withholding and recovery.

RESULT

Water deficit negatively impacted growth parameters, including shoot dry weight, root dry weight and leaf area, in all hybrids; however, the C1 demonstrated relatively minor reductions compared to the other hybrids. Glycine betaine content in leaves increased by 49.4% in C9-4 and 47% in C1, while only 7% and 11% increases were found in the most sensitive clones, C8-3 and C4-2. Notably, C9-4, identified as the most tolerant clone, displayed the highest proline levels, with increases of 29.5% in leaves and 41.5% in roots, in contrast to C8-3, which showed minimal increases of 6% and 11% in leaves and roots, respectively. Clones with higher compatible solutes maintained higher relative water content (RWC), lower osmotic potential and smaller reductions in leaf water potential. RWC declined by just 6% in C9-4, whereas it dropped by 88% in C8-3. Osmotic potentials in C9-4 were - 1.61 MPa in leaves and - 0.271 MPa in roots, while in C8-3, they were - 0.93 MPa and - 0.11 MPa in leaves and roots, respectively. Following recovery, evaluations of growth, physiological traits and visual observations indicated that C8-3 had poor recovery ability. Heatmap and PCA analyses categorized the clones into three groups: "tolerant" (C9-4, C1 and C2), "moderately tolerant" (UCB1) and "sensitive" (C8-3, C4-2 and C16-1).

CONCLUSION

The results of this study underscore the significance of osmotic adjustment as a more critical trait compared to growth and stomatal parameters in effectively differentiating tolerant clones from sensitive ones.

A 50-year look-back on the efficacy of limited transpiration traits: does the evidence support the recent surge in interest?

We examine limited transpiration (LT) traits in crop species, which are claimed to conserve early season water for critical late season growth. Despite there being theoretical support for LT crops, we suggest that there is insufficient empirical evidence to support the general acceptance of this theory. Our criticism focuses on two main points: the undervaluation of early season carbon assimilation and investment over the lifetime of the plant; and the overestimation of soil water savings. We argue that forgoing early season water use, and therefore also future investment in deeper and denser roots (improved resource acquisition), will negatively impact plant performance in many soil and climate contexts. Furthermore, we challenge the assumption that conserved soil water remains available for later use without loss, noting significant losses resulting from evaporation and other sinks. We advocate for a re-evaluation of LT traits, incorporating a balance of water and carbon dynamics throughout a plant's lifetime. We caution against the adoption of LT traits where they have not been empirically evaluated in the soils and climates of interest to individual research and breeding programs. We propose a more physiologically integrated approach to crop improvement, focusing on water extraction efficiency and strategic carbon investment.

Xanthophyll cycle and photosynthetic electron transport enhanced by galactolipid modification alleviate drought-induced leaf senescence

Previous studies have demonstrated galactolipid modification was involved in drought-induced leaf senescence. Under drought stress, overactivation of the photosynthetic electron transfer chain leads to excessive light energy absorption, resulting in photooxidative damage to crops. The xanthophyll cycle, a key photoprotective mechanism, mitigates light-induced damage by dissipating excess energy as heat. However, the role of the xanthophyll cycle pigments and photosynthetic electron transport in the process of galactolipid modification alleviates drought-induced leaf senescence has not yet been clarified clearly. In this study, a comparative experiment was conducted to investigate changes in the xanthophyll cycle and photosynthetic electron transport during drought and re-watering in two maize varieties: a drought-tolerant variety (Liangyu66) and a senescent variety (Liangyu99). Drought stress induced more severely wilted and leaf senescence in Liangyu99, with lower shoot biomass, photosynthetic rate, chlorophyll a/b, monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG) content, corresponding gene expression level and DGDG/MGDG ratio compared to Liangyu66. Furthermore, PSII electron transport rate (ETRⅡ), the PSI electron transport rate (ETRⅠ), and cyclic electron flow (CEF) in Liangyu66 were 14 %, 47 %, and 83 % higher, respectively, than in Liangyu99 under drought stress. Notably, the de-epoxidation state of the xanthophyll cycle (A + Z)/(A + Z + V) was significantly higher in Liangyu66 than in Liangyu99. Non-photochemical quenching (NPQ) increased in both varieties under drought stress, Liangyu66 displayed a higher NPQ than Liangyu99. These findings suggest that galactolipid modification alleviates drought-induced leaf senescence by enhancing the xanthophyll cycle and optimizing photosynthetic electron transport.

Alterations in physiological and biochemical characteristics of Prunus sibirica seedlings raised from spaceflight seeds

The aim was to explore the alterations in growth traits, physiological and biochemical characteristics of Prunus sibirica seedlings raised from spaceflight seeds. The seedlings cultivated by the "Shenzhou XII" spacecraft carrying the seeds of superior clones of P. sibirica were used to observe their growth traits and determine physiological indicators. The results showed that plant height of Prunus sibirica seedlings raised from spaceflight seeds increased by 18-34% and internode length increased by 8-26%, but the number of primary branches, secondary branches, and leaves showed no significant change compared to the ground control. Leaf length and width of Prunus sibirica seedlings raised from spaceflight seeds were significantly higher than those of the ground control, with leaf length, width, and area increasing to 1.21-1.80 times higher than that of the ground control. Furthermore, the antioxidant and osmoregulatory capacities of P. sibirica seedlings raised from spaceflight seeds were altered. The peroxidase (POD) activity and Malondialdehyde (MDA) content were increased in ST28, ST207, and ST507, while they were reduced in ST1 and ST453. Compared with the ground control, the content of soluble sugar(SS), starch (St), and free proline (Pro) were significantly or highly significantly increased in all lines. The content of soluble protein (SP) was significantly increased in ST1, ST28, ST207, and ST507, while there was no significant change in ST453. P. sibirica seedlings raised from spaceflight seeds exhibited increased leaf pigment content, the interstitial CO2 concentration (Ci), net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr). In conclusion, compared with the ground control, the growth indexes and physiological characteristics of Prunus sibirica seedlings raised from spaceflight seeds were changed, and the direction of change was different for different lines. This provided a foundation for subsequent germplasm improvement and variety selection.

Sensing, Adapting and Thriving: How Fruit Crops Combat Abiotic Stresses

Production of high-yield and high-quality fruits is always the long-term objective of fruit crop cultivation, which, however, is challenged by various abiotic stresses such as drought, extreme temperatures and high salinity, and the adverse impacts of abiotic stresses on fruit crops are exacerbated by climate change in recent years. To cope with these environmental stressors, fruit crops have evolved adaptative strategies involving physiological changes and molecular regulation. In this review, we summarise the relevent changes in photosynthesis, osmotic and reactive oxygen species (ROS) equilibrium, metabolism and protein homeostasis in response to abiotic stresses. Moreover, perception of environmental stimuli as well as recent progress of underlying regulatory mechanisms is also discussed. Based on our current knowledge, possible strategies for stress resilience improvement in fruit crops are accordingly proposed. In addition, we also discuss the challenges in identification of key nodes in plant responses to multiple stresses and development of stress-resilient fruit crops, and addressing these issues in the future would advance our understanding of how fruit crops combat abiotic stresses and facilitate the breeding of superior fruit crops that can adapt to and thrive in the changing environments.

Synergy of osmotic adjustment and antioxidant activity in Catalpa bungei: alleviating persistent drought stress from SL to NSL

Introduction

Catalpa bungei C. A. Mey is a precious timber and garden tree species native to China. It is mainly distributed in the semi-arid regions of northern China, where drought stress severely affects its growth.

Methods

In this study, we investigated the physiological responses and gene expression profiles of C. bungei seedlings subjected to a 28-day drought stress treatment.

Results and discussion

By reducing stomatal conductance (Cond) and increasing proline (Pro) and soluble sugar contents (SS), C. bungei alleviated mild drought stress (7-14 days). Under moderate drought stress (14-21 days), a synergistic interaction of jasmonic acid (JA) and abscisic acid (ABA) enhanced catalase (CAT) activity and proline (Pro) content, while downregulating guard cell osmotic potential, thereby further decreasing stomatal conductance (Cond). Upon reaching severe drought stress (21-28 days, SWC 22%, LWC 73%), the activity of antioxidant enzymes and the content of osmotic substances continued to increase, while the structure of photosynthetic organs was damaged, resulting in a shift from stomatal limitation (SL) to non-stomatal limitation (NSL). Therefore, C. bungei mitigates mild drought stress through osmotic regulation, and ABA and JA coordinate antioxidant defenses and osmotic regulation as drought persists. Once the shift from SL to NSL caused by severe drought stress, the aforementioned mechanism ceases to be effective in mitigating the deleterious effects of drought stress on C. bungei. These findings enhance our comprehension of the mechanisms underlying C. bungei's response to prolonged drought, providing valuable insights for the precise evaluation of drought intensity and facilitating efficient management of C. bungei plantations.

Green biogenic sulfur nanoparticles enhance Capsicum annuum (L.) resilience to salt stress by triggering physio-biochemical and genetic repair mechanisms

The synthesis of metal nanoparticles is an expanding field of study due to the potential uses in creating new technologies that facilitate the production of crops by improving tolerance against salinity stress. The current study outlined the green synthesis of sulfur nanoparticles (SNPs) using Moringa oleifera (Lam.) leaf extract and its protective role on Capsicum annuum (L.) growth against salinity stress. Using Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD), the effective formation of the synthesized SNPs was examined and approved. The results confirmed the purity and morphology of SNPs. Then, SNPs (1, 10, 100 mg/l) were used in nano-priming to alleviate the adverse effects of NaCl (50, 100 mM) on C. annuum seedlings. The findings demonstrated that C. annuum growth parameters were severely lowered by increasing salinity stress level, whereas SNPs treatments enhanced plant growth under both salt levels. The optimum concentration for alleviating salinity stress was 10 mg/l SNPs. 10 mg/l SNPs significantly increased shoot fresh weight, dry weight, chlorophyll content, cell membrane stability and relative water content by 75.4, 77.8, 82.5, 89.5 and 20.9%, while reduced the water and solute potential, Na+/K+ ratio, proline, glycine betaine, malondialdehyde, H2O2 and superoxide anion content by 45.5, 43.2, 27.7%, 18.1, 40.3, 39.3, 35.4 and 34.5% respectively compared to untreated stressed control at 100 mM NaCl. Moreover, SNPs substantially improved, antioxidant enzymes activities and upregulated the expression of some salt-tolerant genes under saline conditions. Under both salinity levels, the genes CaHAK6, CaHAK7, CaDHN3, CaCAT1 and CaPOD recorded maximum expression at 10 mg/l SNPs. Overall, these findings demonstrate the efficiency of green SNPs as a practical approach to alleviate NaCl-induced stress in C. annuum plants by triggering many physiological, biochemical and genetic repair mechanisms. These results offer a sustainable agri-environmental strategy for mitigating salt stress and enhancing crop production in saline environments.

Water Translocation and Photosynthetic Responses in Clones of Kentucky Bluegrass to Heterogeneous Water Supply

Drought stress is the most common threat to plant growth, while physiological integration can significantly enhance the drought tolerance of clonal plants, making it essential to research the behavior of clones under drought conditions and explore the potential applications of clonal plants. This study applied polyethylene-glycol-6000-induced stress to proximal, middle and distal clonal ramets of Kentucky bluegrass (Poa pratensis L.) and used an isotope labeling technique to evaluate the water physiological integration and photosynthetic capacity. When the proximal ramet was subjected to drought stress treatment, the decrease in 2H isotopes in the roots from 4 h to 6 h was significantly smaller than the increase in 2H isotopes in their own leaves. Additionally, the reductions in δ2H values of middle and distal ramets roots were 4.14 and 2.6 times greater, respectively, than the increases in their respective leaf δ2H values. The results indicate that under drought stress, water physiological integration was observed among different clonal ramets. In addition, drought stress inhibits the photosynthetic-related indicators in clonal ramets, with varying degrees of response and trends in photosynthetic characteristics among different clonal ramets. The proximal ramet treatment group, treated with polyethylene glycol 6000, was most affected by drought stress, while the distal ramet treatment group was least affected. The proximal ramet treatment group, treated with polyethylene glycol 6000, showed a decrease in water use efficiency after 6 h of drought treatment, while the other groups exhibited some increase. This indicates differences in water utilization and regulation among the different clonal ramets under drought stress. This study holds significant theoretical importance for exploring the characteristics of physiological integration and the photosynthetic mechanisms of Kentucky bluegrass clones under drought stress.

Evaluation of Kabuli Chickpea Genotypes for Terminal Drought Tolerance in Tropical Growing Environment

Terminal drought is the major constraint for chickpea production, leading to yield losses of up to 90% in tropical environments. Understanding the morphological, phenological, and physiological traits underlying drought tolerance is crucial for developing resilient chickpea genotypes. This study elucidates the drought-tolerant traits of eight kabuli chickpea genotypes under a controlled environment using polyvinyl chloride (PVC) lysimeters. Terminal drought was imposed after the flowering stage, and the response was assessed against non-stress (well-watered) treatment. Drought stress significantly impacted gas-exchange parameters, reducing the stomatal conductance (16-35%), chlorophyll content (10-22%), carbon assimilation rate (21-40%) and internal carbon concentration (7-14%). Principal component analysis (PCA) indicated three groups among these eight genotypes. The drought-tolerant group included two genotypes (AVTCPK#6 and AVTCPK#19) with higher water use efficiency (WUE), deep-rooted plants, longer maturity, and seed yield stability under drought stress. In contrast, the drought-susceptible group included two genotypes (AVTCPK#1 and AVTCPK#12) that were early-maturing and low-yielding with poor assimilation rates. The intermediate group included four genotypes (AVTCPK#3, AVTCPK8, AVTCPK#24, and AVTCPK#25) that exhibited medium maturity and medium yield, conferring intermediate tolerance to terminal drought. A significantly strong positive correlation was observed between seed yield and key physiological traits (stomatal conductance (gsw), leaf chlorophyll content (SPAD) and carbon assimilation rate (Asat)) and morphological traits (plant height, number of pods, and root biomass). Conversely, carbon discrimination (Δ13C) and intrinsic WUE (iWUE) showed a strong negative correlation with seed yield, supporting Δ13C as a surrogate for WUE and drought tolerance and a trait suitable for the selection of kabuli chickpea genotypes for drought resilience.

Differential impact of commercial rootstocks on the physiological response of a common walnut scion to drought stress

Walnut rootstocks are commonly used in California orchards to provide resistance to soil-borne pests and diseases. However, little information exists about the impact of commercial rootstock on the common scion's physiological response under drought. This is becoming increasingly important since walnuts are commonly cultivated in semi-arid regions where frequent and severe droughts require efficient water use. We previously reported that own-rooted walnut rootstocks (RX1, VX211 and Vlach) differ in their physiological performance under drought. Here, we evaluated whether similar water relations and performance are conferred to a common English walnut scion (Juglans regia cv. Cisco). To do so, we used a mini-lysimeter platform to continuously track soil moisture and transpirational water loss from trees. Along with the canopy's estimated leaf area, changes in canopy shape and texture were evaluated using deep learning as an independent method to analyze canopy response to water stress. In support of our recent findings, the scion grafted onto rootstock RX1 exhibited subtle improvements in physiological performance associated with higher transpiration and canopy conductance under well-watered condition compared to Vlach and VX211 rootstocks. Canopy conductance, texture, and shape were not significantly affected by rootstock under water stress. However, Cisco grafted onto RX1 exhibited higher leaf turgor and water use efficiency, and lower osmotic potentials under water stress. Our results suggest some subtle differences in water relations between the rootstock genotypes, and propose an efficient deep-learning method to screen canopies for water stress-induced response through image processing.

Response of Maize (Zea mays L.) to Foliar-Applied Nanoparticles of Zinc Oxide and Manganese Oxide Under Drought Stress

Maize (Zea mays L.) is an important crop grown for food, feed, and energy. In general, maize yield is decreased due to drought stress during the reproductive stages, and, hence, it is critical to improve the grain yield under drought. A field experiment was conducted with a split-plot design. The main factor was the irrigation regime viz. well-irrigated conditions and withholding irrigation from tasseling to grain filling for 21 days. The subplots include six treatments, namely, (i) the control (water spray), (ii) zinc oxide @ 100 ppm, (iii) manganese oxide @ 20 ppm, (iv) nZnO @ 100 ppm + nMnO @ 20 ppm, (v) Tamil Nadu Agricultural University (TNAU) Nano Revive @ 1.0%, and (vi) zinc sulfate 0.25% + manganese sulfate 0.25%. During drought stress, the anthesis-silking interval (ASI), chlorophyll a and b content, proline, starch, and carbohydrate fractions were recorded. At harvest, the grain-filling rate and duration, per cent green leaf area, and yield traits were recorded. Drought stress increased the proline (38.1%) and anthesis-silking interval (0.45 d) over the irrigated condition. However, the foliar application of ZnO (100 ppm) and nMnO (20 ppm) lowered the ASI and increased the green leaf area, leaf chlorophyll index, and proline content over water spray. The seed-filling rate (17%), seed-filling duration (11%), and seed yield (19%) decreased under drought. Nevertheless, the seed-filling rate (90%), seed-filling duration (13%), and seed yield (52%) were increased by the foliar spraying of nZnO (100 ppm) and nMnO (20 ppm) over water spray. These findings suggest that nZnO and nMnO significantly improve the grain yield of maize under drought stress conditions.

Root sweet root: how date palm uses osmotic adjustment to thrive in arid climates

This article comments on:

Franzisky BL, Mueller HM, Du B, Lux T, White PJ, Carpentier SC, Winkler JB, Schnitzler JP, Kudla J, Kangasjärvi J, Reichelt M, Mithöfer A, Mayer KFX, Rennenberg H, Ache P, Hedrich R, Messerer M, Geilfus CM. 2025. Date palm diverts organic solutes for root osmotic adjustment and protects leaves from oxidative damage in early drought acclimation. Journal of Experimental Botany 76, 1244–1265 https://doi.org/10.1093/jxb/erae456.

Date palm diverts organic solutes for root osmotic adjustment and protects leaves from oxidative damage in early drought acclimation

Date palm (Phoenix dactylifera L.) is an important crop in arid regions and it is well adapted to desert ecosystems. To understand its remarkable ability to grow and yield in water-limited environments, we conducted experiments in which water was withheld for up to 4 weeks. In response to drought, root, rather than leaf, osmotic strength increased, with organic solutes such as sugars and amino acids contributing more to the osmolyte increase than minerals. Consistently, carbon and amino acid metabolism was acclimated toward biosynthesis at both the transcriptional and translational levels. In leaves, a remodeling of membrane systems was observed, suggesting changes in thylakoid lipid composition which, together with the restructuring of the photosynthetic apparatus, indicated an acclimation preventing oxidative damage. Thus, xerophilic date palm avoids oxidative damage under drought by combined prevention and rapid detoxification of oxygen radicals. Although minerals were expected to serve as cheap key osmotics, date palm also relies on organic osmolytes for osmotic adjustment in the roots during early drought acclimation. The diversion of these resources away from growth is consistent with the date palm strategy of generally slow growth in harsh environments and clearly indicates a trade-off between growth and stress-related physiological responses.

Physiological and Transcriptome Analysis Reveal the Underlying Mechanism of Salicylic Acid-Alleviated Drought Stress in Kenaf (Hibiscus cannabinus L.)

Salicylic acid (SA) plays a crucial role in alleviating drought stress in plants. However, little is known about the molecular mechanisms underlying exogenous SA on the drought tolerance of kenaf. In this study, the kenaf seedlings were subjected to physiological and transcriptomic analysis under control (CK), moderate drought stress (D), and moderate drought stress with 1 mM SA (D_SA). Under drought conditions, SA significantly improved the plant biomass, leaf area, antioxidant enzyme activities (SOD, POD, and CAT), soluble sugars, starch and proline contents, and photosynthesis, while the contents of MDA, H2O2, and O2- were significantly decreased. A total of 3430 (1118 up-regulated and 2312 down-regulated) genes were differentially expressed in group D, compared with group CK. At the same time, 92 (56 up-regulated and 36 down-regulated) genes were differentially expressed in group D_SA compared with group D. GO and KEGG analysis showed that the differentially expressed genes (DEGs) were enriched in various metabolic pathways, such as carbohydrate metabolism, lipid metabolism, and the metabolism of terpenoids and polyketides. Results showed that the genes related to the antioxidant system, sucrose and starch synthesis, osmoregulation, ABA signal regulation, and differentially expressed transcription factors, such as AP2/ERF4 and NF-Y1, were involved in the increased drought tolerance of kenaf under exogenous SA. Virus-induced gene silencing (VIGS)-mediated silencing of salicylate binding protein 2 gene (HcSABP2) decreased the drought resistance of kenaf seedlings. Thus, the present study provides valuable insights into the regulatory mechanism of exogenous SA in alleviating drought stress in kenaf.

Synergistic Effects of Zinc Oxide Nanoparticles and Moringa Leaf Extracts on Drought Tolerance and Productivity of Cucurbita pepo L. Under Saline Conditions

This study investigated the combined effects of zinc oxide nanoparticles (Nano-Zn) and moringa leaf extract (MLE) on squash plants grown under water stress conditions in saline soil during 2021-2022. The research compared full irrigation (100% ETc) with water deficit conditions (60% ETc). While water deficit negatively impacted plant growth, yield, and various physiological parameters, the sequential application of Nano-Zn (at 50 or 100 mg L-1) with MLE (3%) significantly mitigated these adverse effects. The combined treatment proved more effective than individual applications, enhancing growth parameters, photosynthetic efficiency, and antioxidant systems. The treatment particularly improved stress tolerance by increasing protective compounds like soluble sugars and amino acids while reducing harmful H2O2 levels. The study concluded that sequential application of 100 mg L-1 Nano-Zn with MLE was optimal for enhancing squash performance under drought stress, with 50 mg L-1 Nano-Zn plus MLE as the second-best option.

Melatonin induces drought stress tolerance by regulating the physiological mechanisms, antioxidant enzymes, and leaf structural modifications in Rosa centifolia L

Melatonin is considered an effective bio-stimulant that is crucial in managing several abiotic stresses including drought. However, its potential mechanisms against drought stress in fragrant roses are not well understood. Here, we aim to investigate the role of melatonin on Rosa centifolia plants cultivated under drought stress (40 % field capacity) and normal irrigation (80 % field capacity). Plant growth traits, gaseous exchange, antioxidants, osmolytes, oxidative stress, and leaf anatomical attributes were measured. All pots were arranged with a completely randomized design with two-factor factorial setup. Foliar application of melatonin was carried out on the next day of drought treatment and was repeated weekly, while normal watering was regarded as control. Drought stress significantly enhanced oxidative stress markers and reduced growth parameters in water-deficit rose plants. However, melatonin spray (100 μM) produced increased plant height (16 %), flower yield (16 %), petal fresh and dry biomass (7 % and 38 %), total chlorophyll (48 %), contents of carotenoid (54 %), and gaseous exchange traits such as stomatal conductance (25 %), photosynthetic rate (91 %), and transpiration rate (3 %), in water-deficient plants. Likewise, the accretion of catalase, superoxide dismutase, soluble protein, proline, and glycine betaine contents was recorded by 22 %, 45 %, 58 %, 7 %, and 6 %, respectively, in drought-stressed plants, due to melatonin treatment. Increment of oxidative stress indicators i.e. malondialdehyde (-37 %) and hydrogen peroxide (-27 %) was diminished by melatonin triggered by drought stress. Furthermore, leaf cortex (51 %), vascular bundle area (76 %), palisade cell area (59 %), and lamina thickness (42 %) were remarkably increased with melatonin foliar sprays in water-deficit plants. The results of this study recommend that melatonin is a protective agent against drought stress and has potential application prospects in the rose-producing regions suffering from water deficiency. Future studies should focus on molecular responses of R. centifolia to drought stress to further develop stress alleviation strategies in floricultural crops.

Effects of acid and aluminum stress on seed germination and physiological characteristics of seedling growth in Sophora davidii

Sophora davidii, a vital forage species, predominantly thrives in the subtropical karst mountains of Southwest China. Its resilience to poor soil conditions and arid environments renders it an ideal pioneer species for ecological restoration in these regions. This study investigates the influence of acidic, aluminum-rich local soil on the germination and seedling growth physiology of S. davidii. Experiments were conducted under varying degrees of acidity and aluminum stress, employing three pH levels (3.5 to 5.5) and four aluminum concentrations (0.5 to 2.0 mmol·L-1). The results showed that germination rate, germination index, and vigor index of S. davidii seeds were decreased but not significantly under slightly acidic conditions (pH 4.5-5.5), while strong acid (pH = 3.5) significantly inhibited the germination rate, germination index, and vigor index of white spurge seeds compared with the control group. Aluminum stress (≥0.5 mmol·L-1) significantly inhibited the germination rate, germination index, and vigor index of S. davidii seed. Moreover, the seedlings' root systems were sensitive to the changes of aluminum concentration, evident from significant root growth inhibition, characterized by root shortening and color deepening. Notably, under aluminum stress (pH = 4.3), the levels of malondialdehyde and proline in S. davidii escalated with increasing aluminum concentration, while antioxidant enzyme activities demonstrated an initial increase followed by a decline. The study underscores the pivotal role of cellular osmoregulatory substances and protective enzymes in combating aluminum toxicity in S. davidii, a key factor exacerbating growth inhibition in acidic environments. These findings offer preliminary theoretical insights for the practical agricultural utilization of S. davidii in challenging soil conditions.

Protein-Based Mechanism of Wheat Growth Under Salt Stress in Seeds Irradiated with Millimeter Waves

Wheat is one of the most extensively grown crops in the world; however, its productivity is reduced due to salinity. This study focused on millimeter wave (MMW) irradiation to clarify the salt-stress tolerance mechanism in wheat. In the present study, wheat-root growth, which was suppressed to 77.6% of the control level under salt stress, was recovered to the control level by MMW irradiation. To reveal the salt-stress tolerance mechanism of MMW irradiation on wheat, a proteomic analysis was conducted. Proteins related to cell cycle, proliferation, and transport in biological processes, as well as proteins related to the nucleus, cytoskeleton, and cytoplasm within cellular components, were inversely correlated with the number of proteins. The results of the proteomic analysis were verified by immunoblot and other analyses. Among the proteins related to the scavenging reactive-oxygen species, superoxide dismutase and glutathione reductase accumulated under salt stress and further increased in the MMW-irradiated wheat. Among pathogen-related proteins, pathogenesis-related protein 1 and the Bowman-Birk proteinase inhibitor decreased under salt stress and recovered to the control level in the MMW-irradiated wheat. The present results indicate that MMW irradiation of wheat seeds improves plant-growth recovery from salt stress through regulating the reactive oxygen species-scavenging system and the pathogen-related proteins. These genes may contribute to the development of salt-stress-tolerant wheat through marker-assisted breeding and genome editing.

Multi-Trait Index-Based Selection of Drought Tolerant Wheat: Physiological and Biochemical Profiling

Drought is a detrimental abiotic stress that severely limits wheat growth and productivity worldwide by altering several physiological processes. Thus, understanding the mechanisms of drought tolerance is essential for the selection of drought-resilient features and drought-tolerant cultivars for wheat breeding programs. This exploratory study evaluated 14 wheat genotypes (13 relatively tolerant, one susceptible) for drought endurance based on flag leaf physiological and biochemical traits during the critical grain-filling stage in the field conditions. Measurements included six physiological, seven gas exchange, six photosystem II, six stomatal, three reactive species, seven metabolomic solutes, and two biomass traits. All parameters were significantly influenced by drought, with varying genotypic responses. Hierarchical cluster analysis (HCA) categorized genotypes into three drought tolerance groups based on trait performance. Seven genotypes in Cluster 2 (BARI Gom 26, BARI Gom 33, BD-631, BD-600, BD-9910, BD-9889, BD-637) exhibited superior drought tolerance, characterized by minimal changes in physiological traits and biomass accumulation, reduced oxidative stress markers, and increased accumulation of osmoprotectants. The innovative multi-trait genotype-ideotype distance index (MGIDI) further ranked wheat genotypes in regard to drought tolerance, identifying BARI Gom 33, BARI Gom 26, BD-9889, and BD-600 as top performers. Notably, all these top-ranking genotypes belonged to Cluster 2, previously identified as the highest-performing group in the HCA. The identified genotypes with superior drought tolerance offer valuable genetic resources for enhancing wheat productivity in water-limiting environments. Traits related to photosynthetic activity, biomass gain, leaf conductance, water stress, and osmoprotection showed high selection differentials and heritability in MGIDI analysis, indicating their potential as selection targets for drought-tolerant wheat. Overall, the strategic approaches have yielded novel insights into genotype screening that can be directly applied to deepen our understanding of drought tolerance mechanisms in wheat.

Osmotic stress in roots drives lipoxygenase-dependent plastid remodeling through singlet oxygen production

Osmotic stress, caused by the lack of water or by high salinity, is a common problem in plant roots. Osmotic stress can be reproducibly simulated with the application of solutions of the high-molecular-weight and impermeable polyethylene glycol. The accumulation of different reactive oxygen species, such as singlet oxygen, superoxide, and hydrogen peroxide, accompany this stress. Among them, singlet oxygen, produced as a byproduct of lipoxygenase activity, has been associated with limiting root growth. To better understand the source and effect of singlet oxygen, we followed its production at the cellular level in Arabidopsis (Arabidopsis thaliana). Osmotic stress initiated profound changes in plastid and vacuole structure. Confocal and electron microscopy showed that the plastids were a source of singlet oxygen accompanied by the appearance of multiple, small extraplastidic bodies that were also an intense source of singlet oxygen. A marker protein, CRUMPLED LEAF, indicated that these small bodies originated from the plastid outer membrane. Remarkably, LINOLEATE 9S-LIPOXYGENASE 5 (LOX5) was shown to change its distribution from uniformly cytoplasmic to a more clumped distribution together with plastids and the small bodies. In addition, oxylipin products of Type 9 lipoxygenase increased, while products of Type 13 lipoxygenases decreased. Inhibition of lipoxygenase by the salicylhydroxamic acid inhibitor or in downregulated lipoxygenase lines prevented cells from initiating the cellular responses, leading to cell death. In contrast, singlet oxygen scavenging halted terminal cell death. These findings underscore the reversible nature of osmotic stress-induced changes, emphasizing the pivotal roles of lipoxygenases and singlet oxygen in root stress physiology.

Unraveling water relations in growing fruit: insights from the epidermal growth regulation hypothesis

This review focuses on the intricate water relationships between internal and external tissues in growing fruits within the framework of the epidermal growth control hypothesis. It considers the components of water potential, including turgor pressure and osmotic potential of both internal and external tissues, taking into account factors such as fruit growth rate, sugar accumulation, cell wall metabolism, and climacteric. It also examines the effects of environmental conditions, genetic factors, and physiological influences in modifying water relations. By emphasizing the significance of skin tissue water potential components as indicators of growth stress, the review underlines their importance for a comprehensive understanding of water relations and associated physiological disorders in growing fruit.

Ubiquitin Ligase U-Box51 Positively Regulates Drought Stress in Potato (Solanum tuberosum L.)

The ubiquitin-proteasome system (UPS) is a key protein degradation pathway in eukaryotes, in which E3 ubiquitin ligases mediate protein ubiquitination, directly or indirectly targeting substrate proteins to regulate various biological processes, including plant growth, hormone signaling, immune responses, and adaptation to abiotic stress. In this study, we identified plant U-box protein 51 in Solanum tuberosum (StPUB51) as an E3 ubiquitin ligase through transcriptomic analysis, and used it as a candidate gene for gene-function analysis. Quantitative real-time PCR (qRT-PCR) was used to examine StPUB51 expression across different tissues, and its expression patterns under simulated drought stress induced by polyethylene glycol (PEG 6000) were assessed. Transgenic plants overexpressing StPUB51 and plants with down-regulated StPUB51 expression were generated to evaluate drought tolerance. The activities of key antioxidant enzymes-superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) as well as malondialdehyde (MDA) content in transgenic plants' leaves were measured under drought conditions. Protein-protein interactions involving StPUB51 were explored via yeast two-hybrid (Y2H) screening, with interaction verification by bimolecular fluorescence complementation (BiFC). StPUB51 was predominantly expressed in stems, with lower expression observed in tubers, and its expression was significantly upregulated in response to 20% PEG-6000 simulated drought. Subcellular localization assays revealed nuclear localization of the StPUB51 protein. Under drought stress, StPUB51-overexpressing plants exhibited enhanced SOD, POD, and CAT activities and reduced MDA levels, in contrast to plants with suppressed StPUB51 expression. Y2H and BiFC analyses identified two interacting proteins, StSKP2A and StGATA1, which may be functionally linked to StPUB51. Collectively, these findings suggest that StPUB51 plays a positive regulatory role in drought tolerance, enhancing resilience in potato growth and stress adaptation.

Effect of kaolin on productivity, anatomical and biochemical responses to water deficit in Pelargonium graveolens grown in sandy soil

The objective of this study was to examine the response of geranium plants to different irrigation levels (100%, 80%, and 60% based on ETo) and Kaolin application rates (0, 100, 200 and 300 ppm) during 2022 and 2023 seasons, at Aly Mobarak Experimental Farm, Horticulture Research Station, located at El-Bustan site, El-Behiera Governorate, Egypt, by using a two-way factorial analysis experimental design. The results revealed that water deficit significantly reduced most studied traits. Irrigation level at 60% based on ETo exhibited poorest performance on growth parameters and decreased fresh yield and essential oil yield by 27.77% 10.73%, respectively as compared with full irrigated plants. However, foliar application of kaolin at 200 and 300 ppm led to increasing biomass accumulation by 28.51, 26.16%, and essential oil yield by 79.51, 89.95%, respectively, as compared with untreated plants grown under the same level of water deficit (60% based on ETo). GC-MS analysis of essential oil showed that water deficit and kaolin application increased geraniol/citronellol ratio and consequently improved oil quality. Results highlight the positive influence of water deficit and kaolin rates on the development and performance of anatomical parameters. Enzymes assay in leaves revealed in an increase superoxide dismutase (SOD) and peroxidase (POD) activities, and decreased in catalase (CAT) activity under water deficit. As for WUE at 60%, followed by 80% based on ETo recorded excellent response for geranium plants which led to more water saving. So, it could be concluded that foliar application of kaolin at 200 and 300 ppm obtained the optimal characteristics of geranium plants under experimental conditions. In particular, essential oil yield and productivity.

Effects of water deficit on two cultivars of Hibiscus mutabilis: A comprehensive study on morphological, physiological, and metabolic responses

Hibiscus mutabilis, commonly known as the cotton rose, is a widely cultivated ornamental and has been acclaimed as the representative flower of the 2024 World Horticultural Exposition. The growth and ornamental characteristics of Hibiscus mutabilis can be affected by drought stress. Therefore, we investigated the physiological and metabolic responses of drought-sensitive Hibiscus mutabilis JRX-1 and drought-tolerant Hibiscus mutabilis CDS-4 under drought stress. The results of the physiological analyses revealed that, compared to JRX-1,CDS-4 maintained good growth and greater water use efficiency through stronger antioxidant defences, osmoregulatory capacity and stomatal regulation. A total of 3277 metabolites were identified in positive and negative ion modes, of which 663 metabolites presented changes in expression under drought conditions, including 306 upregulated metabolites and 357 downregulated metabolites. Secondary metabolites, such as flavonoids and diterpenoids, are crucial in the plant response to drought stress. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that the differentially aboundant metabolites were significantly enriched in the pathways valine, leucine and isoleucine degradation; linoleic acid metabolism; one carbon pool by folate; and folate biosynthesis. The results of this study will not only help to elucidate and apply the physiological and metabolic regulatory strategies of Hibiscus mutabilis to improve its adaptation to water deficit conditions, but will also provide valuable guidance to breeders and molecular biologists in the screening and use of drought resistant genes in ornamental plants.

Dehydration tolerance rather than avoidance explains drought resistance in zoysiagrass

Irrigation of grasses dominates domestic water use across the globe, and better understanding of water use and drought resistance in grasses is of undeniable importance for water conservation. Breeding programs have released cultivars with improved drought resistance, but the underlying mechanisms remain unknown. We sought to characterize the mechanisms driving drought resistance in four zoysiagrass cultivars (Lobo, Zeon, Empire, and Meyer) reported to exhibit contrasting levels of drought resistance. A dry-down was performed through deficit irrigation until 70% decline in evapotranspiration. All cultivars exhibited similar drought avoidance as they dehydrated similarly throughout the drought. Lobo and Zeon, however, exhibited a 70% decline in evapotranspiration two to three days after Empire and Meyer, thus experiencing lower water potentials. Regarding drought tolerance, Lobo and Zeon maintained higher normalized difference vegetation index (NDVI) and lower perceived canopy mortality at higher dehydration levels than Empire and Meyer. We use "perceived" because visual assessments of canopy mortality are influenced by drought-induced leaf rolling. During the recovery, leaves rehydrated and unrolled, so the "actual" canopy mortality could be evaluated. All cultivars exhibited similar mortality on the first recovery day despite Lobo and Zeon experiencing more severe dehydration. Throughout the recovery, Lobo and Empire exhibited faster re-growth and showed the lowest canopy mortality, and Lobo exhibited the highest NDVI. The improved drought resistance of Lobo and Zeon results from greater dehydration tolerance rather than avoidance. This study has implications for lawn owners selecting the best cultivars and for breeding programs aiming at improving drought resistance of zoysiagrasses.

Drought Tolerance in Plants: Physiological and Molecular Responses

Drought, a significant environmental challenge, presents a substantial risk to worldwide agriculture and the security of food supplies. In response, plants can perceive stimuli from their environment and activate defense pathways via various modulating networks to cope with stress. Drought tolerance, a multifaceted attribute, can be dissected into distinct contributing mechanisms and factors. Osmotic stress, dehydration stress, dysfunction of plasma and endosome membranes, loss of cellular turgidity, inhibition of metabolite synthesis, cellular energy depletion, impaired chloroplast function, and oxidative stress are among the most critical consequences of drought on plant cells. Understanding the intricate interplay of these physiological and molecular responses provides insights into the adaptive strategies plants employ to navigate through drought stress. Plant cells express various mechanisms to withstand and reverse the cellular effects of drought stress. These mechanisms include osmotic adjustment to preserve cellular turgor, synthesis of protective proteins like dehydrins, and triggering antioxidant systems to counterbalance oxidative stress. A better understanding of drought tolerance is crucial for devising specific methods to improve crop resilience and promote sustainable agricultural practices in environments with limited water resources. This review explores the physiological and molecular responses employed by plants to address the challenges of drought stress.

Phytoremediation potential of Brazilian mahogany (Swietenia macrophylla King) on exposure to nickel: anatomical, biochemical and antioxidant responses

The advancement and intensification of industrial and mining activities has generated a series of impacts on natural ecosystems, combined with the inappropriate use of agrochemicals and the erroneous disposal of electronic products, contributing to soil contamination with a diversity of chemical elements, including heavy metals. Due to this, this work aimed to evaluate the effect of increasing dosages of nickel on the anatomy, biochemistry and oxidative system of Brazilian mahogany (Swietenia macrophylla), a forest species from the Amazon, seeking to indicate the potential use of this species in phytoremediation programs. of soils contaminated with heavy metals. The seeds were grown under a constant temperature of 28°C, relative humidity (RH) of 90% with a 12-hour photoperiod for 43 days. The experimental design used was randomized blocks (DBC), with five treatments (0, 2, 4, 6 and 8 mg.L-1 of Nickel), with six replications. Data were subjected to analysis of variance (ANOVA) and means were tested for significant differences using the Tukey test at 5% significance. Changes in the anatomy of the different organs were observed, with differences in the cells in the central region of the leaf, the stem and the root. The concentration of total carbohydrates had no statistical differences with the application of nickel, however changes were observed in photosynthetic pigments, reducing sugars and sucrose as an adaptive form to nickel. The increase in nickel dosages was accompanied by the synthesis of ammonium, amino acids and proline in the root, while the synthesis of glycine was reduced. In the leaf, there was an increase in amino acids with an increase in metal, accompanied by a decrease in glycine. The plant antioxidant defense system was efficient in attenuating the toxic effects of ROS, with significant actions of CAT and SOD enzymes in the root, while the leaf had the main action of APX and CAT. The cultivation of mahogany plants can be advocated to mitigate Ni pollution in these areas, as this forest species has a particular characteristic of resistance to stressful conditions in contact with the heavy metal.

Rice homolog of Arabidopsis Xylem NAC domain 1 (OsXND1), a NAC transcription factor regulates drought stress responsive root system architecture in indica rice

Rice yield is greatly constrained by drought stress. In Arabidopsis, XYLEM NAC DOMAIN 1 (XND1) gene regulates the xylem formation, efficiency of water transport, and the delicate equilibrium between drought tolerance and resistance to pathogens. However, diversity and the role of rice homologs of OsXND1 is not reported so far. This study hypothesized that the rice homolog of OsXND1 also regulates drought stress tolerance through modulation of root architecture. Initially, phylogenetic analysis identified two OsXND1 homologs (Os02g0555300 and Os04g0437000) in rice. Further, 14 haplotypes were identified in the OsXND1 of which Hap1 and Hap3 were major haplotypes. The association analysis of OsXND1 with 16 different traits, including 10 root traits, showed three SNPs (Chr02:20972728-Promoter variant; Chr02:20972791-5' UTR variant, and Chr02:20973745-3' UTR variant) were significantly associated with root area, root surface area, total root length, and convex hull area only under drought stress in indica rice. Besides, the superior haplotype of OsXND1 increased the root area, root surface area, total root length, and convex hull area by 46%, 40%, 38%, and 42%, respectively, under drought stress conditions. Therefore, the identified superior haplotype of OsXND1 can be utilized in haplotype breeding programs for the improvement of drought tolerance in rice.

Exogenous application of serotonin, with the modulation of redox homeostasis and photosynthetic characteristics, enhances the drought resistance of the saffron plant

Water stress is one of the most significant abiotic stresses that disrupts the osmotic balance of plants and consequently reduces their growth and performance. In recent years, it has been found that serotonin, as a signaling and regulatory molecule, can play important roles in the growth and development of plants and enhance their tolerance to abiotic stresses. Saffron is a plant known for its medicinal and culinary properties. Its distinct flavor, aroma, and vibrant color make it a sought-after ingredient in various cuisines and traditional medicines. The aim of this study is to investigate the possible effect of serotonin growth regulator on some morphophysiological and biochemical characteristics of saffron plant under water stress conditions. Water stress was applied using polyethylene glycol 6000 at a level of 30%, w/v. Serotonin was also applied exogenously at a concentration of 100 µM in both foliar and root applications. The experimental findings demonstrated that water stress had a detrimental impact on various growth and photosynthetic parameters including FW, DW, SH, RWC, photosynthetic pigments content, Pn, Fv/Fm, C and Ci. Under these conditions, H2O2 content and ion leakage increased. The increase in the content of proline and sugars also confirmed that the saffron plant was placed in unfavorable growth conditions. Serotonin application in both foliar and root applications and especially root treatment under stressful conditions improved plant growth by activating enzymatic and non-enzymatic antioxidant systems. Overall, the exogenous application of serotonin increased the resistance of saffron plants to water stress.

Transcriptome and Metabolome Analyses Reveal the Molecular Mechanisms of Albizia odoratissima's Response to Drought Stress

Albizia odoratissima is a deciduous tree species belonging to the family Leguminosae. It is widely distributed in the southern subtropical and tropical areas of China and has important ecological and economic value. The growth and metabolic processes of A. odoratissima are affected by drought stress, but the molecular mechanisms remain unknown. Therefore, this study investigated the physicochemical properties, gene expression, and metabolites of A. odoratissima seedlings under drought stress. The results show that, in leaves of A. odoratissima seedlings, drought stress reduced the moisture content, chlorophyll content, photosynthetic efficiency, superoxide dismutase (SOD) activity, and gibberellin (GA) and indoleacetic acid (IAA) contents while increasing the catalase (CAT) and peroxidase (POD) activities and malondialdehyde (MDA), proline, soluble sugar, and soluble protein contents. Within the CK5 (Day 5 of control group) vs. T5 (Day 5 of drought treatment), CK10 vs. T10, CK15 vs. T15, and CK20 vs. T20 groups (CK: control group; T: drought treatment), a total of 676 differentially expressed genes (DEGs) were upregulated and 518 DEGs were downregulated, and a total of 228 and 143 differential accumulation metabolites (DAMs) were identified in the CK10 vs. T10 and CK20 vs. T20 groups. These were mainly involved in the amino acid and alkaloid metabolism pathways in the leaves of the A. odoratissima seedlings. In the amino acid and alkaloid biosynthesis pathways, the relative expression levels of the AoproA (Aod04G002740, ORTHODONTIC APPLIANCE), AoOAT (Aod07G015970, ORNITHINE-OXO-ACID TRANSAMINASE), and AoAOC3 (Aod12G005010/08G003360/05G023920/08G003000/08G003010, AMINE OXIDASE COPPER CONTAINING 3) genes increased, which concurrently promoted the accumulation of arginine, proline, piperine, cadaverine, and lysine. Furthermore, some key transcription factors in the response to drought were identified in the leaves using the weighted gene co-expression network analyses (WGCNA) method. These findings reveal that A. odoratissima seedlings respond to drought stress by improving the capacities of the antioxidant system and secondary metabolism.

Regional differences in leaf evolution facilitate photosynthesis following severe drought

Characterizing physiological and anatomical changes that underlie rapid evolution following climatic perturbation can broaden our understanding of how climate change is affecting biodiversity. It can also provide evidence of cryptic adaptation despite stasis at higher levels of biological organization. Here, we compared evolutionary changes in populations of Mimulus cardinalis from historically different climates in the north and south of the species' range following an exceptional drought. We grew seeds produced from predrought ancestral plants alongside peak-drought descendants in a common glasshouse and exposed them to wet and dry conditions. Before the drought, northern ancestral populations expressed traits contributing to drought escape, while southern ancestral populations expressed drought avoidance. Following the drought, both regions evolved to reduce water loss and maintain photosynthesis in dry treatments (drought avoidance), but via different anatomical alterations in stomata, trichomes, and palisade mesophyll. Additionally, southern populations lost the ability to take advantage of wet conditions. These results reveal rapid evolution towards drought avoidance at an anatomical level following an exceptional drought, but suggest that differences in the mechanisms between regions incur different trade-offs. This sheds light on the importance of characterizing underlying mechanisms for downstream life-history and macromorphological traits.

Effect of bio-fertilizers and seaweed extract on growth and yield of wheat (Triticum aestivum L.) under different irrigation regimes: Two-year field study

Wheat productivity is constrained by genetic, agronomic, and climate factors, though it is an important crop for food production worldwide. The present study evaluated the effect of bio-fertilizer consortia and seaweed extracts on the growth and yield of two wheat varieties under different irrigation regimes in a field study. This experiment was conducted in a split-split plot based on a randomized complete block design with four replications in 2018 and 2019. Irrigation treatments were the main factor, wheat variety (Sardari and Sirvan) the sub-factor, and bio-fertilizers the sub-sub-factors. The results showed that irrigation regimes significantly improved leaf width, number of leaves, fresh weight of roots and shoots, osmotic potential, leaf water content, and number of stomata respectively by 57.53, 38.59, 106.65, 135.29, 87.92, 14.22 and 13.77, 88.02 and 96.11 percent compared to dry-land conditions. Applying one- and two-times irrigation increased grain yield by 51% and 79%, respectively, and the response varied in wheat varieties. Sardari variety due to having smaller leaf dimensions (Leaf length and width) and lower fresh and dry weight of roots and shoots, as well as lower leaf and tissue water content, had lower grain yield than the Sirvan variety. All the bio-fertilizers positively impacted the growth and yield of both varieties. However, the highest average grain yield in the first and second years of the experiment (with an average of 5226.25 and 4923.33 kg/ha, respectively) were found under the combined application of Mycorrhiza + Nitrozist and Phosphozist + Seaweed extract. The results of the present study underscore the importance of irrigation regimes and consortia of bio-fertilizers for improving grain yield. This study also highlighted the resilience of the studied wheat varieties and bio-fertilizers to projected climate changes. These findings could provide insights into adaptive strategies for mitigating the impact of climate change on wheat production.

Poly-γ-glutamic acid enhanced the yield and photosynthesis of soybeans by adjusting soil aggregates and water distribution

BACKGROUND

Poly-γ-glutamic acid (γ-PGA) is employed extensively in agriculture to enhance soil water retention; however, the underlying mechanism by which γ-PGA improves soil structure and soybean productivity in arid regions remains poorly understood. A micro-scale field experiment was conducted in the arid region of northwest China, employing five concentrations of γ-PGA to investigate its impacts on soybean yield, photosynthesis, and water-use efficiency, as well as soil aggregates and water distribution. The five levels of γ-PGA were 0 (CK), 10 (P1), 20 (P2), 40 (P3), and 80 kg ha-1 (P4).

RESULTS

The results demonstrated that the application of γ-PGA significantly improved soybean yield, photosynthesis, and chlorophyll content. It resulted in a decrease in soil aggregate content with a maximum diameter of less than 0.053 mm and an increase in the stability of soil aggregates in the uppermost layer of the soil (0-30 cm). The application of γ-PGA significantly increased soil water content, particularly in the uppermost layer of the soil, and effectively reduced water consumption and improving water use efficiency in soybeans. Overall, the P3 treatment exhibited the most pronounced improvement of soybean yield, photosynthesis, water-use efficiency, as well as distribution of soil aggregates and water. The correlation matrix heatmap also revealed a strong correlation between improvement of soybean yield or photosynthesis at various γ-PGA application levels and the enhancement of soil stability or soil water content.

CONCLUSION

The multivariate regression analysis revealed that an optimal application level of 46 kg ha-1 γ-PGA could enhance effectively both yield and water use efficiency of soybean in the arid region of northwest China. © 2024 Society of Chemical Industry.

Physiological and Molecular Mechanisms of Rice Tolerance to Salt and Drought Stress: Advances and Future Directions

Rice, a globally important food crop, faces significant challenges due to salt and drought stress. These abiotic stresses severely impact rice growth and yield, manifesting as reduced plant height, decreased tillering, reduced biomass, and poor leaf development. Recent advances in molecular biology and genomics have uncovered key physiological and molecular mechanisms that rice employs to cope with these stresses, including osmotic regulation, ion balance, antioxidant responses, signal transduction, and gene expression regulation. Transcription factors such as DREB, NAC, and bZIP, as well as plant hormones like ABA and GA, have been identified as crucial regulators. Utilizing CRISPR/Cas9 technology for gene editing holds promise for significantly enhancing rice stress tolerance. Future research should integrate multi-omics approaches and smart agriculture technologies to develop rice varieties with enhanced stress resistance, ensuring food security and sustainable agriculture in the face of global environmental changes.

Adaptive strategies to drought stress in grasses of the poaceae family under climate change: Physiological, genetic and molecular perspectives: A review

Drought stress is one of the most critical abiotic factors which negatively impacts on growth, productivity, and survival of plants. Grass species have an important role in the sustainable intensification of cropping systems. This review focus on the specific drought tolerance characteristics in grass species and application of prevalent classical and molecular methods for genetic improvement of them to drought stress. Generally, grass species adapt to drought stress by utilizing more than one strategy including of changes in the root growth, photosynthetic pigments, activation of antioxidant enzymes, and accumulation of compatible osmolytes. They also have other specific characteristics consisted of summer dormancy, drought recovery, and persistence, which lead to drought adaptation after prolonged drought. Studies on different grasses, indicated that most of above mentioned traits usually have positive correlation with drought tolerance. Also, high heritability has been reported for most of them in different grasses. Therefore, an effective index might be considering in identification of drought tolerance genotypes. Recently, high-throughput imaging phenotyping and advanced molecular techniques such as genotyping-by-sequencing (GBS), RNA sequencing, genome-wide association study, and genome editing help conventional breeding methods to increase the accuracy, selection efficiency, genetic gains, and speed of breeding programs for developing drought tolerant cultivars.

Surviving the stress: Understanding the molecular basis of plant adaptations and uncovering the role of mycorrhizal association in plant abiotic stresses

Environmental stresses severely impair plant growth, resulting in significant crop yield and quality loss. Among various abiotic factors, salt and drought stresses are one of the major factors that affect the nutrients and water uptake by the plants, hence ultimately various physiological aspects of the plants that compromises crop yield. Continuous efforts have been made to investigate, dissect and improve plant adaptations at the molecular level in response to drought and salinity stresses. In this context, the plant beneficial microbiome presents in the rhizosphere, endosphere, and phyllosphere, also referred as second genomes of the plant is well known for its roles in plant adaptations. Exploration of beneficial interaction of fungi with host plants known as mycorrhizal association is one such special interaction that can facilitates the host plants adaptations. Mycorrhiza assist in alleviating the salinity and drought stresses of plants via redistributing the ion imbalance through translocation to different parts of the plants, as well as triggering oxidative machinery. Mycorrhiza association also regulates the level of various plant growth regulators, osmolytes and assists in acquiring minerals that are helpful in plant's adaptation against extreme environmental stresses. The current review examines the role of various plant growth regulators and plants' antioxidative systems, followed by mycorrhizal association during drought and salt stresses.

Surface modified ZnO NPs by betaine and proline build up tomato plants against drought stress and increase fruit nutritional quality

Drought stress is a serious challenge for global food production. Nanofertilizers and nanocomposites cope with such environmental stresses and also increase nutritional contents of fruits. An in vitro experiment was designed to use Zinc Oxide Nanoparticles (ZnO NPs) primed with Proline and Betaine (ZnOP and ZnOBt NPs) at 50 and 100 mg/kg soil against drought stress in Tomato (Solanum lycopersicum) plants. Plant morphological, biochemical, and fruit nutritional quality were accessed. Maximum plant height was observed under the treatment of ZnOP50 (1.09 m) and ZnO 100 (1.06 m). ZnOP and ZnOBt also improved the chlorophyll content up to 86% and 87.16%, respectively. Application of ZnOP NPs also demonstrated maximum tomato yield (204 g tomato/plant) followed by ZnO NPs and ZnOBt NPs. Nanocomposites decreased phenolics and flavonoids contents in drought stressed plants demonstrating the mitigation of oxidative stress. Nanofertilizer also increased the concentration of phenolics and flavonoids in fruits that increased the nutritional contents. Furthermore a significant accumulation of betaine, proline, and lycopene in fruits on nanocomposite treatment made it nutritional and healthy. Lycopene content increased up to 2.01% and 1.23% in presence of ZnOP50 and ZnOP100, respectively. These outcomes validate that drought stress in plant can be reduced by accumulation of different phytochemicals and quenching oxidative stress. The study deems that nano zinc carrying osmoregulators can greatly reduce the negative effects of drought stress and increase nutritional quality of tomato fruits.

Coping with extremes: Responses of Quercus robur L. and Fagus sylvatica L. to soil drought and elevated vapour pressure deficit

Climate change, particularly droughts and heat waves, significantly impacts global photosynthesis and forest ecosystem sustainability. To understand how trees respond to and recover from hydrological stress, we investigated the combined effects of soil moisture and atmospheric vapour pressure deficit (VPD) on seedlings of the two major European broadleaved tree species Fagus sylvatica (FS) and Quercus robur (QR). The experiment was conducted under natural forest gap conditions, while soil water availability was strictly manipulated. We monitored gas exchange (net photosynthesis, stomatal conductance and transpiration rates), nonstructural carbohydrates (NSC) concentration in roots and stomatal morphometry (size and density) during a drought period and recovery. Our comparative empirical study allowed us to distinguish and quantify the effects of soil drought and VPD on stomatal behavior, going beyond theoretical models. We found that QR conserved water more conservatively than FS by reducing transpiration and regulating stomatal conductance under drought. FS maintained higher stomatal conductance and transpiration at elevated VPD until soil moisture became critically low. QR showed higher intrinsic water use efficiency than FS. Stomata density and size also likely played a role in photosynthetic rate and speed of recovery, especially since QR with its seasonal adjustments in stomatal traits (smaller, more numerous stomata in summer leaves) responded and recovered faster compared to FS. Our focal species showed different responses in NSC content under drought stress and recovery, suggesting possible different evolutionary pathways in coping with stress. QR mobilized soluble sugars, while FS relied on starch mobilization to resist drought. Although our focal species often co-occur in mixed forests, our study showed that they have evolved different physiological, morphological and biochemical strategies to cope with drought stress. This suggests that ongoing climate change may alter their competitive ability and adaptive potential in favor of one of the species studied.

Growth and non-structural carbohydrates response patterns of Eucommia ulmoides under salt and drought stress

Introduction

Salinity and droughts are severe abiotic stress factors that limit plant growth and development. However, the differences and similarities of non-structural carbohydrates (NSCs) responses patterns of trees under the two stress conditions remain unclear.

Methods

We determined and compared the growth, physiology, and NSCs response patterns and tested the relationships between growth and NSCs concentrations (or pool size) of Eucommia ulmoides seedlings planted in field under drought and salt stress with different intensities and durations.

Results and discussion

We found that drought and salt stress can inhibit the growth of E. ulmoides, and E. ulmoides tended to enhance its stress resistance by increasing proline concentration and leaf thickness or density but decreasing investment in belowground biomass in short-term stress. During short-term drought and salt stress, the aboveground organs showed different NSCs response characteristics, while belowground organs showed similar change characteristics: the starch (ST) and NSCs concentrations in the coarse roots decreased, while the ST and soluble sugar (SS) concentrations in the fine roots increased to enhance stress resistance and maintain water absorption function. As salt and drought stress prolonged, the belowground organs represented different NSCs response patterns: the concentrations of ST and SS in fine roots decreased as salt stress prolonged; while ST in fine roots could still be converted into SS to maintain water absorption as drought prolonged, resulting in an increase of SS and a decrease of ST. Significant positive relationships were found between growth and the SS and total NSCs concentrations in leaves and branches, however, no significant correlations were found between growth and below-ground organs. Moreover, relationships between growth and NSCs pool size across organs could be contrast.

Conclusion

Our results provide important insights into the mechanisms of carbon balance and carbon starvation and the relationship between tree growth and carbon storage under stress, which were of great significance in guiding for the management of artificial forest ecosystem under the context of global change.

Seasonality drives leaf solute potential independently from drought in grapevines. A commentary on 'Grape cultivars adapted to hotter, drier growing regions exhibit greater photosynthesis in hot conditions despite less drought-resistant leaves'

This article comments on:

Gabriela Sinclair, Erin R. Galarneau, Josh F. Hnizdor, Andrew J. McElrone, Michael Andrew Walker and Megan K. Bartlett, Grape cultivars adapted to hotter, drier growing regions exhibit greater photosynthesis in hot conditions despite less drought-resistant leaves, Annals of Botany, Volume 134, Issue 2, 1 August 2024, Pages 205–217 https://doi.org/10.1093/aob/mcae032

Grape cultivars adapted to hotter, drier growing regions exhibit greater photosynthesis in hot conditions despite less drought-resistant leaves

BACKGROUND AND AIMS

Many agricultural areas are expected to face hotter, drier conditions from climate change. Understanding the mechanisms that crops use to mitigate these stresses can guide breeding for more tolerant plant material. We tested relationships between traits, physiological function in hot conditions and historical climate associations to evaluate these mechanisms for winegrapes. We expected a more negative leaf osmotic potential at full hydration (πo), which reduces leaf turgor loss during drought, and either a metabolically cheaper or more osmoprotectant leaf chemical composition, to allow cultivars associated with hot, dry regions to maintain greater gas exchange in hot growing conditions.

METHODS

We measured πo, gas exchange and leaf chemistry for seven commercially important winegrape cultivars that vary widely in historical climate associations. Vines were grown in common-garden field conditions in a hot wine-growing region (Davis, CA, USA) and measured over the hottest period of the growing season (July-September).

KEY RESULTS

The value of πo varied significantly between cultivars, and all cultivars significantly reduced πo (osmotically adjusted) over the study period, although osmotic adjustment did not vary across cultivars. The value of πo was correlated with gas exchange and climate associations, but in the direction opposite to expected. Photosynthesis and πo were higher in the cultivars associated with hotter, less humid regions. Leaf chemical composition varied between cultivars but was not related to climate associations.

CONCLUSIONS

These findings suggest that maintenance of leaf turgor is not a primary limitation on grapevine adaptation to hot or atmospherically dry growing conditions. Thus, selecting for a more negative πo or greater osmotic adjustment is not a promising strategy to develop more climate-resilient grape varieties, contrary to findings for other crops. Future work is needed to identify the mechanisms increasing photosynthesis in the cultivars associated with hot, dry regions.

Leaf drought adaptive response in winter oilseed rape is altered at the onset of senescence: a study combining NMR relaxometry, multi-omics and microscopy

Climate change is bringing more frequent and intense droughts, reducing overall water availability and adversely affecting crops. There is a need to improve our understanding of the tissular and cellular adaptation mechanisms that are critical for plant water conservation strategies. Here, we have used NMR relaxometry in combination with microscopy and multi-omic analysis to study the effects of progressive soil drought on winter oilseed rape (WOSR, Brassica napus L., cv. Aviso) leaves. This study reveals the structural and metabolic adjustments these leaves operate to maintain cell homeostasis. Our results are original in showing that the adaptive responses are altered in leaves at the onset of senescence, associated with changes in metabolic plasticity and mesophyll structures. Thus, long-term responses in young leaves involving osmotic adjustment were combined with the maintenance of tissue hydration and cell growth, contributing to high survival and recovery capacity. For the first time, short-term responses observed in early senescent-old leaves were associated with early drought-induced dehydration of the spongy layer. However, this dehydration was not followed by osmotic adjustment and did not allow maintenance of leaf tissue turgor. These findings open further studies on the genetic variability of drought responses related to identified short- and long-term structural and metabolic plasticity traits in Brassica species.

Management of Tomato Bacterial Canker Disease by the Green Fabricated Silver Nanoparticles

Bacterial canker disease caused by Clavibacter michiganensis is a substantial threat to the cultivation of tomatoes, leading to considerable economic losses and global food insecurity. Infection is characterized by white raised lesions on leaves, stem, and fruits with yellow to tan patches between veins, and marginal necrosis. Several agrochemical substances have been reported in previous studies to manage this disease but these were not ecofriendly. Thus present study was designed to control the bacterial canker disease in tomato using green fabricated silver nanoparticles (AgNps). Nanosilver particles (AgNPs) were synthesized utilizing Moringa oleifera leaf extract as a reducing and stabilizing agent. Synthesized AgNPs were characterized using UV-visible spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray (EDX), and Fourier transform infrared spectrometry (FTIR). FTIR showed presence of bioactive compounds in green fabricated AgNPs and UV-visible spectroscopy confirmed the surface plasmon resonance (SPR) band in the range of 350 nm to 355 nm. SEM showed the rectangular segments fused together, and XRD confirmed the crystalline nature of the synthesized AgNPs. The presence of metallic silver ions was confirmed by an EDX detector. Different concentrations (10, 20, 30, and 40 ppm) of the green fabricated AgNPs were exogenously applied on tomato before applying an inoculum of Clavibacter michigensis to record the bacterial canker disease incidence at different day intervals. The optimal concentration of AgNPs was found to be 30 µg/mg that exhibited the most favorable impact on morphological (shoot length, root length, plant fresh and dry weights, root fresh and dry weights) and physiological parameters (chlorophyll contents, membrane stability index, and relative water content) as well as biochemical parameters (proline, total soluble sugar and catalase activity). These findings indicated a noteworthy reduction in biotic stress through the increase of both enzymatic and non-enzymatic activities by the green fabricated AgNPs. This study marks a first biocompatible approach in assessing the potential of green fabricated AgNPs in enhancing the well-being of tomato plants that affected with bacterial canker and establishing an effective management strategy against Clavibacter michiganensis. This is the first study suggests that low concentration of green fabricated nanosilvers (AgNPs) from leaf extract of Moringa oleifera against Clavibacter michiganensis is a promisingly efficient and eco-friendly alternative approach for management of bacterial canker disease in tomato crop.

Individual and interactive effects of amino acid and paracetamol on growth, physiological and biochemical aspects of Brassica napus L. under drought conditions

Drought stress poses a significant threat to Brassica napus (L.), impacting its growth, yield, and profitability. This study investigates the effects of foliar application of individual and interactive pharmaceutical (Paracetamol; 0 and 250 mg L-1) and amino acid (0 and 4 ml/L) on the growth, physiology, and yield of B. napus under drought stress. Seedlings were subjected to varying levels of drought stress (100% field capacity (FC; control) and 50% FC). Sole amino acid application significantly improved chlorophyll content, proline content, and relative water contents, as well as the activities of antioxidative enzymes (such as superoxide dismutase and catalase) while potentially decreased malondialdehyde and hydrogen peroxide contents under drought stress conditions. Pearson correlation analysis revealed strong positive correlations between these parameters and seed yield (R2 = 0.8-1), indicating their potential to enhance seed yield. On the contrary, sole application of paracetamol exhibited toxic effects on seedling growth and physiological aspects of B. napus. Furthermore, the combined application of paracetamol and amino acids disrupted physio-biochemical functions, leading to reduced yield. Overall, sole application of amino acids proves to be more effective in ameliorating the negative effects of drought on B. napus.

Water for agriculture: more crop per drop

Global crop production in agriculture depends on water availability. Future scenarios predict increasing occurrence of flash floods and rapidly developing droughts accompanied by heatwaves in humid regions that rely on rain-fed agriculture. It is challenging to maintain high crop yields, even in arid and drought-prone regions that depend on irrigation. The average water demand of crops varies significantly, depending on plant species, development stage, and climate. Most crops, such as maize and wheat, require relatively more water during the vegetative phase compared to the ripening phase. In this review, we explain WUE and options to improve water use and thus crop yield. Nutrient management might represent another possibility to manipulate water uptake and use by plants. An emerging topic involves agroforest co-cultivation, where trees in the system facilitate water transfer through hydraulic lift, benefiting neighbouring crops. Other options to enhance crop yield per water use are discussed.

Genetic engineering of drought- and salt-tolerant tomato via Δ1-pyrroline-5-carboxylate reductase S-nitrosylation

Drought and soil salinization substantially impact agriculture. While proline's role in enhancing stress tolerance is known, the exact molecular mechanism by which plants process stress signals and control proline synthesis under stress is still not fully understood. In tomato (Solanum lycopersicum L.), drought and salt stress stimulate nitric oxide (NO) production, which boosts proline synthesis by activating Δ1-pyrroline-5-carboxylate synthetase (SlP5CS) and Δ1-pyrroline-5-carboxylate reductase (SlP5CR) genes and the P5CR enzyme. The crucial factor is stress-triggered NO production, which regulates the S-nitrosylation of SlP5CR at Cys-5, thereby increasing its NAD(P)H affinity and enzymatic activity. S-nitrosylation of SlP5CR enables tomato plants to better adapt to changing NAD(P)H levels, boosting both SlP5CR activity and proline synthesis during stress. By comparing tomato lines genetically modified to express different forms of SlP5CR, including a variant mimicking S-nitrosylation (SlP5CRC5W), we found that SlP5CRC5W plants show superior growth and stress tolerance. This is attributed to better P5CR activity, proline production, water use efficiency, reactive oxygen species scavenging, and sodium excretion. Overall, this study demonstrates that tomato engineered to mimic S-nitrosylated SlP5CR exhibits enhanced growth and yield under drought and salt stress conditions, highlighting a promising approach for stress-tolerant tomato cultivation.

Seed osmopriming with polyethylene glycol (PEG) enhances seed germination and seedling physiological traits of Coronilla varia L. under water stress

Water stress can adversely affect seed germination and plant growth. Seed osmopriming is a pre-sowing treatment in which seeds are soaked in osmotic solutions to undergo the first stage of germination prior to radicle protrusion. Seed osmopriming enhances germination performance under stressful environmental conditions, making it an effective method to improve plant resistance and yield. This study analyzed the effect of seed osmopriming with polyethylene glycol (PEG) on seed germination and physiological parameters of Coronilla varia L. Priming treatments using 10% to 30% PEG enhanced germination percentage, germination vigor, germination index, vitality index, and seedling mass and reduced the time to reach 50% germination (T50). The PEG concentration that led to better results was 10%. The content of soluble proteins (SP), proline (Pro), soluble sugars (SS), and malondialdehyde (MDA) in Coronilla varia L. seedlings increased with the severity of water stress. In addition, under water stress, electrolyte leakage rose, and peroxidase (POD) and superoxide dismutase (SOD) activities intensified, while catalase (CAT) activity increased at mild-to-moderate water stress but declined with more severe deficiency. The 10% PEG priming significantly improved germination percentage, germination vigor, germination index, vitality index, and time to 50% germination (T50) under water stress. Across the water stress gradient here tested (8 to 12% PEG), seed priming enhanced SP content, Pro content, and SOD activity in Coronilla varia L. seedlings compared to the unprimed treatments. Under 10% PEG-induced water stress, primed seedlings displayed a significantly lower MDA content and electrolyte leakage than their unprimed counterparts and exhibited significantly higher CAT and POD activities. However, under 12% PEG-induced water stress, differences in electrolyte leakage, CAT activity, and POD activity between primed and unprimed treatments were not significant. These findings suggest that PEG priming enhances the osmotic regulation and antioxidant capacity of Coronilla varia seedlings, facilitating seed germination and seedling growth and alleviating drought stress damage, albeit with reduced efficacy under severe water deficiency.

Not so hidden anymore: Advances and challenges in understanding root growth under water deficits

Limited water availability is a major environmental factor constraining plant development and crop yields. One of the prominent adaptations of plants to water deficits is the maintenance of root growth that enables sustained access to soil water. Despite early recognition of the adaptive significance of root growth maintenance under water deficits, progress in understanding has been hampered by the inherent complexity of root systems and their interactions with the soil environment. We highlight selected milestones in the understanding of root growth responses to water deficits, with emphasis on founding studies that have shaped current knowledge and set the stage for further investigation. We revisit the concept of integrated biophysical and metabolic regulation of plant growth and use this framework to review central growth-regulatory processes occurring within root growth zones under water stress at subcellular to organ scales. Key topics include the primary processes of modifications of cell wall-yielding properties and osmotic adjustment, as well as regulatory roles of abscisic acid and its interactions with other hormones. We include consideration of long-recognized responses for which detailed mechanistic understanding has been elusive until recently, for example hydrotropism, and identify gaps in knowledge, ongoing challenges, and opportunities for future research.