Proline accumulation in leaves of Periploca sepium via both biosynthesis up-regulation and transport during recovery from severe drought

Synergistic effects of foliar applied glycine betaine and proline in enhancing rice yield and stress resilience under salinity conditions

Soil salinity is one of the most challenging environmental factors affecting rice productivity, particularly in regions with high saline soils such as Egypt. The ability of rice to maintain high yield and quality under saline stress is often limited, leading to significant reductions in productivity. With the increasing salinization of agricultural lands, finding effective agronomic practices and treatments to mitigate salt-induced damage in rice crops is critical for ensuring food security. This study investigates the potential of exogenous glycine betaine (GB) and proline (Pro) applications to mitigate the adverse effects of salt stress on rice (cv. Sakha 108) over two consecutive growing seasons (2021-2022). Treatments of 30 mM GB and 30 mM Pro significantly enhanced dry weight (162.2 and 169.7 g in 2021 and 2022, respectively), plant height (88.94 and 99.00 cm), tiller number (10.58 and 10.33), and grain yield (4.22 and 4.30 t/ha) compared to control groups. Combined treatments of 30 mM GB and 30 mM Pro exhibited the greatest improvements across both years, with maximum dry weight (193.44 and 186.56 g), plant height (112.00 and 112.33 cm), tiller number (15.33 and 16.28), spikelet number per meter (264.00 and 264.05), thousand-kernel weight (70.00 and 73.2 g), and grain yield (6.17 and 6.64 t/ha). Additionally, the combined treatments resulted in the highest harvest index (53.22% in 2021 and 48.94% in 2022), amylose content (24.24% and 20.09%), and protein content (12.33% and 12.00%). Correlation analysis highlighted strong positive relationships among traits, such as plant height with grain yield (r = 0.94), biomass yield (r = 0.92), and harvest index (r = 0.90). Path analysis further demonstrated that thousand-kernel weight and biomass yield had the most significant direct effects on grain yield, with values of 0.43 and 0.42, respectively. Heatmap clustering and principal component analysis (PCA) confirmed the synergistic effects of combined GB and Pro treatments, with the 30P_30GB treatment consistently clustering with high-yield traits, enhancing nitrogen use efficiency and stress resilience. In conclusion, the combined application of glycine betaine and proline significantly enhances the agronomic and chemical traits of rice under salt stress. This study demonstrates that these osmoprotectants improve vegetative growth, grain yield, and quality, with synergistic effects observed at optimal concentrations. The findings highlight the potential of glycine betaine and proline as effective tools for improving salt tolerance in rice, offering practical solutions to address challenges in saline-affected agricultural regions.

In vitro and in vivo screening for the identification of salt-tolerant sugarcane (Saccharum officinarum L.) clones: molecular, biochemical, and physiological responses to salt stress

Sugarcane is a glycophyte whose growth and yield can be negatively affected by salt stress. As the arable lands with potential saline soils expand annually, the increase of salt-tolerance in sugarcane cultivars is highly desired. We, herein, employed in vitro and in vivo conditions in order to screen sugarcane plants for salt tolerance at the cellular and at the whole plant levels. Calli of sugarcane cv. Khon Kaen 3 (KK3) were selected after culturing in selective media containing various NaCl concentrations, and regenerated plants were then reselected after culturing in selective media containing higher NaCl concentrations. The surviving plants were finally selected after an exposure to 254 mM NaCl under greenhouse conditions. A total of 11 sugarcane plants survived the selection process. Four plants that exhibited tolerance to the four different salt concentrations applied during the aforementioned screening process were then selected for the undertaking of further molecular, biochemical, and physiological studies. The construction of a dendrogram has revealed that the most salt-tolerant plant was characterized by the lowest genetic similarity to the original cultivar. The relative expression levels of six genes (i.e., SoDREB, SoNHX1, SoSOS1, SoHKT, SoBADH, and SoMIPS) were found to be significantly higher in the salt-tolerance clones than those measured in the original plant. The measured proline levels, the glycine betaine content, the relative water content, the SPAD unit, the contents of chlorophyll a and b, as well as the K⁺/Na⁺ ratios of the salt-tolerant clones were also found to be significantly higher than those of the original plant.When the salt-tolerant clones were grown in a low saline soil, they exhibited a higher Brix percentage than that of the original cultivar.

Comparative analysis of remediation efficiency and ultrastructural translocalization of polycyclic aromatic hydrocarbons in Medicago sativa, Helianthus annuus, and Tagetes erecta

Polycyclic aromatic hydrocarbons (PAHs) are semi-volatile anthropogenic contaminants that can damage soil fertility and threaten the environment due to their hazardous effects on various ecological parameters. The experimental objective was divided into two parts because PAHs are always present in mixtures. The toxicity of anthracene, phenanthrene, pyrene, and fluoranthene was examined and investigated the potential of three phytoremediator plants species viz Tagetes erecta, Helianthus annuus, and Medicago sativa for remediation and translocation of individual PAH. PAHs were shown to have inhibitory or stimulating effects on growth, antioxidant properties, and impact on the structure of plant cells. The result showed that M. sativa significantly enhances the removal rate of PAHs in the soil. The dissipation rate reached 96.2% in M. sativa planted soil, followed by H. annuus and T. erecta. Among the plant species, M. sativa exhibited the highest root and shoot concentrations (314.37 and 169.55 mg kg-1), while the lowest concentration was 187.56 and 76.60 mg kg-1 in T. erecta. SEM-EDX and fluorescence micrographs confirmed that pyrene altered plant tissue's ultrastructure and cell viability and was found to be the most toxic and resistant. M. sativa was proven to be the most effective plant for the mitigation of PAHs.

Effect of Water Stress and Shading on Lime Yield and Quality

The aim of this study was to test the combined effect of water stress and cropping system on yield and fruit quality in Bearss lime trees. For this purpose, two irrigation treatments were applied during stage II of fruit growth: control (well irrigated, automatically managed by soil water content sensors) and stress (non-irrigated), both under open-field and shaded conditions. Soil water status was assessed by determining soil water content and plant water status by measuring stem water potential (Ψ_stem), stomatal conductance (g_s), and net photosynthesis (P_n). Yield parameters (kg and the number of fruits per tree and fresh mass per fruit) and fruit quality were assessed on two harvest dates. In addition, on the second harvest date, the content of metabolites and nutrients in the lime juice was analyzed. The results showed that soil water deficit induced 35% lower g_s values in open-field than in shaded conditions. The highest kg and the number of fruits per tree were observed in the shaded system, especially on the first harvest date. The lowest yield was observed in stressed trees grown without netting. Slightly higher fresh mass and equatorial diameter were observed in shaded fruits than in open-field fruit. Soil water deficit increased fruit total soluble solids and decreased juice content, especially in open-field trees. Shaded conditions made the lime trees more resilient to soil water deficit, which led to higher yields and better external fruit quality traits. In addition, fruit precocity was significantly higher in the shaded system.

Drought and Subsequent Soil Flooding Affect the Growth and Metabolism of Savoy Cabbage

An important factor of current climate change is water availability, with both droughts and flooding becoming more frequent. Effects of individual stresses on plant traits are well studied, although less is known about the impacts of sequences of different stresses. We used savoy cabbage to study the consequences of control conditions (well-watered) versus continuous drought versus drought followed by soil flooding and a potential recovery phase on shoot growth and leaf metabolism. Under continuous drought, plants produced less than half of the shoot biomass compared to controls, but had a >20% higher water use efficiency. In the soil flooding treatment, plants exhibited the poorest growth performance, particularly after the "recovery" phase. The carbon-to-nitrogen ratio was at least twice as high, whereas amino acid concentrations were lowest in leaves of controls compared to stressed plants. Some glucosinolates, characteristic metabolites of Brassicales, showed lower concentrations, especially in plants of the flooding treatment. Stress-specific investment into different amino acids, many of them acting as osmolytes, as well as glucosinolates, indicate that these metabolites play distinct roles in the responses of plants to different water availability conditions. To reduce losses in crop production, we need to understand plant responses to dynamic climate change scenarios.

Transcriptome and Metabolome Analyses Reveal Potential Salt Tolerance Mechanisms Contributing to Maintenance of Water Balance by the Halophytic Grass Puccinellia nuttalliana

Elevated soil salinity exacerbated by human activities and global climate change poses serious threats to plant survival. Although halophytes provide many important clues concerning salt tolerance in plants, some unanswered questions remain to be addressed, including the processes of water and solute transport regulation. We performed high-throughput RNA-sequencing in roots and metabolome characterizations in roots and leaves of Puccinellia nuttalliana halophytic grass subjected to 0 (control) and 150 mM NaCl. In RNAseq, a total of 31 Gb clean bases generated were de novo assembled into 941,894 transcripts. The PIP2;2 and HKT1;5 transcript levels increased in response to the NaCl treatment implying their roles in water and ion homeostasis. Several transcription factors, including WRKY39, DEK3, HY5, and ABF2, were also overexpressed in response to NaCl. The metabolomic analysis revealed that proline and dopamine significantly increased due to the upregulation of the pathway genes under salt stress, likely contributing to salt tolerance mechanisms. Several phosphatidylcholines significantly increased in roots suggesting that the alterations of membrane lipid composition may be an important strategy in P. nuttalliana for maintaining cellular homeostasis and membrane integrity under salt stress. In leaves, the TCA cycle was enriched suggesting enhanced energy metabolism to cope with salt stress. Other features contributing to the ability of P. nuttalliana to survive under high salinity conditions include salt secretion by the salt glands and enhanced cell wall lignification of the root cells. While most of the reported transcriptomic, metabolomics, and structural alterations may have consequences to water balance maintenance by plants under salinity stress, the key processes that need to be further addressed include the role of the changes in the aquaporin gene expression profiles in the earlier reported enhancement of the aquaporin-mediated root water transport.

Root NRT, NiR, AMT, GS, GOGAT and GDH expression levels reveal NO and ABA mediated drought tolerance in Brassica juncea L

Little is known about the interactive effects of exogenous nitric oxide (NO) and abscisic acid (ABA) on nitrogen (N) metabolism and related changes at molecular and biochemical levels under drought stress. The present study highlights the independent and combined effect of NO and ABA (grouped as "nitrate agonists") on expression profiles of representative key genes known to be involved in N-uptake and assimilation, together with proline metabolism, N-NO metabolism enzyme's activity and nutrient content in polyethylene glycol (PEG) treated roots of Indian mustard (B. juncea cv. Varuna). Here we report that PEG mediated drought stress negatively inhibited growth performance, as manifested by reduced biomass (fresh and dry weight) production. Total N content and other nitrogenous compounds (NO3-, NO2-) were decreased; however, NH4+, NH4+/ NO3- ratio and total free amino acids content were increased. These results were positively correlated with the PEG induced changes in expression of genes and enzymes involved in N-uptake and assimilation. Also, PEG supply lowered the content of macro- and micro-nutrients but proline level and the activity of ∆1-pyrroline-5-carboxylate synthetase increased indicating increased oxidative stress. However, all these responses were reversed upon the exogenous application of nitrate agonists (PEG + NO, PEG + NO + ABA, and PEG + ABA) where NO containing nitrate agonist treatment i.e. PEG + NO was significantly more effective than PEG + ABA in alleviating drought stress. Further, increases in activities of L-arginine dependent NOS-like enzyme and S-nitrosoglutathione reductase were observed under nitrate agonist treatments. This indicates that the balanced endogenous change in NO and ABA levels together during synthesis and degradation of NO mitigated the oxidative stress in Indian mustard seedlings. Overall, our results reveal that NO independently or together with ABA may contribute to improved crop growth and productivity under drought stress.

Different methods of silicon application attenuate salt stress in sorghum and sunflower by modifying the antioxidative defense mechanism

Soil salinization is the most common abiotic stress limiting agricultural productivity worldwide. Recent research has suggested that the application of silicon (Si) has beneficial effects against salt stress in sorghum (Sorghum bicolor L. Moench) and sunflower (Helianthus annuus L.) by regulating the antioxidant system, mineral nutrients, and other important mechanisms. However, whether these effects can be achieved through foliar application of Si, or whether Si application affects Si-accumulating (e.g., sorghum), and intermediate-Si-accumulating (e.g., sunflower) plant species differently, remains unclear. This study investigated different methods of Si application in attenuating the detrimental effects of salt stress, based on the biological responses of two distinct species of Si accumulators, under greenhouse conditions. Two pot experiments were designed as a factorial (2 × 4), randomized complete blocks design (RCBD) with control and salt-stress groups (0 and 100 mmol.L^-1 NaCl), and four Si-treatment groups: control (no Si), foliar application (28.6 mmol.L^-1), root application (2 mmol.L^-1), and combined foliar and root applications. Our results showed that the harmful effects of salt stress were attenuated by Si treatments in both plant species, which decreased Na⁺ uptake and lipid peroxidation, and increased Si and K⁺ uptake, relative leaf water content, antioxidant enzyme activities, leaf area, and shoot dry matter. These results were more prominent when Si was applied via nutrient solution in the sorghum plants, and the combined foliar and root applications of Si in sunflower plants. In addition, foliar application of Si alone is an efficient alternative in attenuating the effects of salinity in both plant species when Si is not available in the growth medium. These results suggest that the Si application method plays an important role in Na⁺ detoxification by modifying the antioxidative defense mechanism, which could actively mediate some important physiological and biochemical processes and helps to increase the shoot dry matter production in sorghum and sunflower plants under salt stress.

Abscisic acid and stress induced by salt: Effect on the phenylpropanoid, L-ascorbic acid and abscisic acid metabolism of strawberry fruits

Strawberry is one of the most popular fruits because of its sensorial and functional properties. However, strawberry crop is sensitive to salt stress conditions. Despite plants have plasticity, high salt concentrations induce molecular, biochemical, and physiological responses in plants. There is evidence that the abscisic acid (ABA) hormone acts as a signaling molecule under stress conditions; however, the molecular mechanisms involved in the synthesis and homeostasis of ABA and in the induction of phytochemical antioxidant compounds under stress conditions remain unclear. In this study, the effect of stress induced by NaCl (salt stress - SS), with or without the simultaneous application of ABA, on the ABA, phenylpropanoids and L-ascorbic acid (AsA) metabolisms were evaluated. The physiological aspects (Na, Cl and proline concentration, photosynthetic variables) were also studied. The results showed that salt stress increases the Na and Cl content in the leaves, affects photosynthetic variables and triggers the production of proline, pelargonidin-3-O-glucoside, total phenolic compounds and AsA content, alongside the upregulation of several genes from the phenylpropanoid and flavonoid pathways. These effects were accompanied by the induction of compounds and transcripts related to ABA biosynthesis, conjugation and catabolism. Otherwise, the exogenous application of ABA in salt stressed plants promotes a shift in gene expression and metabolism to mitigate the stress. Therefore, salt stress affects the metabolism of ABA, phenylpropanoids and AsA in strawberry increasing phytochemical composition which is strongly associated with an ABA-dependent mechanism.

AhHDA1-mediated AhGLK1 promoted chlorophyll synthesis and photosynthesis regulates recovery growth of peanut leaves after water stress

Peanut (Arachis hypogaea L.) is an important crop that is adversely affected by drought. Post-drought growth is essential for improving peanut productivity and quality. Previous studies demonstrated that AhGLK1 (Arachis hypogaea L. Golden2-like 1) activates the expression of AhPORA to stimulate chlorophyll biosynthesis, and that AhGLK1 physically interacts with AhHDA1 (Arachis hypogaea L. histone deacetylase 1). However, the roles of the AhGLK1/AhHDA1 interaction in post-drought recovery remain to be elucidated. Herein, we report that AhHDA1 binds to AhGLK1 promoter and alters histone deacetylation levels to inhibit AhGLK1 expression. RNA-seq confirms that chlorophyll synthesis and photosynthesis-related genes are induced in AhGLK1-overexpressing, but reduced in AhGLK1 RNAi hairy roots. Furthermore, ChIP-seq shows that AhCAB (Arachis hypogaea L. chlorophyll A/B binding protein) is a target of both AhHDA1 and AhGLK1. Transactivation assays reveal that AhGLK1 activates AhCAB expression, while AhHDA1 inhibits the effect of AhGLK1 on AhCAB and AhPORA transcription. ChIP-qPCR shows that AhHDA1 and AhGLK1 bind to the promoters of AhCAB and AhPORA to regulate their expression during water stress and recovery. We propose that AhHDA1 and AhGLK1 consist of an ON/OFF switch for AhCAB and AhPORA expression during water stress and recovery. AhGLK1 activates, whereas AhHDA1 suppresses the expression of AhCAB and AhPORA.

Physiological characterization of a pepper hybrid rootstock designed to cope with salinity stress

In pepper crops, rootstocks that tolerate salt stress are not used because available commercial rootstocks offer limited profits. In this context, we obtained the hybrid NIBER®, a new salinity-tolerant rootstock that has been tested under real salinity field conditions for 3 years with 32%-80% higher yields than ungrafted pepper plants. This study aimed to set up the initial mechanisms involved in the salinity tolerance of grafted pepper plants using NIBER® as a rootstock to study root-shoot behavior, a basic requirement to develop efficient rootstocks. Gas exchange, Na⁺/K⁺, antioxidant capacity, nitrate reductase activity, ABA, proline, H₂O₂, phenols, MDA concentration and biomass were measured in ungrafted plants of cultivar Adige (A), self-grafted (A/A), grafted onto NIBER® (A/N) and reciprocal grafted plants (N/A), all exposed to 0 mM and 70 mM NaCl over a 10-day period. Salinity significantly and quickly decreased photosynthesis, stomatal conductance and nitrate reductase activity, but to lower extent in A/N plants compared to A, A/A and N/A. A/N plants showed decreases in the Na⁺/K⁺ ratio, ABA content and lipid peroxidation activity. This oxidative damage alleviation in A/N was probably due to an enhanced H₂O₂ level that activates antioxidant capacity to cope salinity stress, and acts as a signal molecule rather than a damaging one by contributing a major increase in phenols and, to a lesser extent, in proline concentration. These traits led to a minor impact on biomass in A/N plants under salinity conditions. Only the plants with the NIBER® rootstock controlled the scion by modulating responses to salinity.

Identification of Factors Linked to Higher Water-Deficit Stress Tolerance in Amaranthus hypochondriacus Compared to Other Grain Amaranths and A. hybridus, Their Shared Ancestor

Water deficit stress (WDS)-tolerance in grain amaranths (Amaranthus hypochondriacus, A. cruentus and A. caudatus), and A. hybridus, their presumed shared ancestor, was examined. A. hypochondriacus was the most WDS-tolerant species, a trait that correlated with an enhanced osmotic adjustment (OA), a stronger expression of abscisic acid (ABA) marker genes and a more robust sugar starvation response (SSR). Superior OA was supported by higher basal hexose (Hex) levels and high Hex/sucrose (Suc) ratios in A. hypochondriacus roots, which were further increased during WDS. This coincided with increased invertase, amylase and sucrose synthase activities and a strong depletion of the starch reserves in leaves and roots. The OA was complemented by the higher accumulation of proline, raffinose, and other probable raffinose-family oligosaccharides of unknown structure in leaves and/or roots. The latter coincided with a stronger expression of Galactinol synthase 1 and Raffinose synthase in leaves. Increased SnRK1 activity and expression levels of the class II AhTPS9 and AhTPS11 trehalose phosphate synthase genes, recognized as part of the SSR network in Arabidopsis, were induced in roots of stressed A. hypochondriacus. It is concluded that these physiological modifications improved WDS in A. hypochondriacus by raising its water use efficiency.

The Role of the Plant Antioxidant System in Drought Tolerance

Water deficiency compromises plant performance and yield in many habitats and in agriculture. In addition to survival of the acute drought stress period which depends on plant-genotype-specific characteristics, stress intensity and duration, also the speed and efficiency of recovery determine plant performance. Drought-induced deregulation of metabolism enhances generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) which in turn affect the redox regulatory state of the cell. Strong correlative and analytical evidence assigns a major role in drought tolerance to the redox regulatory and antioxidant system. This review compiles current knowledge on the response and function of superoxide, hydrogen peroxide and nitric oxide under drought stress in various species and drought stress regimes. The meta-analysis of reported changes in transcript and protein amounts, and activities of components of the antioxidant and redox network support the tentative conclusion that drought tolerance is more tightly linked to up-regulated ascorbate-dependent antioxidant activity than to the response of the thiol-redox regulatory network. The significance of the antioxidant system in surviving severe phases of dehydration is further supported by the strong antioxidant system usually encountered in resurrection plants.

Induced, Imprinted, and Primed Responses to Changing Environments: Does Metabolism Store and Process Information?

Metabolism is the system layer that determines growth by the rate of matter uptake and conversion into biomass. The scaffold of enzymatic reaction rates drives the metabolic network in a given physico-chemical environment. In response to the diverse environmental stresses, plants have evolved the capability of integrating macro- and micro-environmental events to be prepared, i.e., to be primed for upcoming environmental challenges. The hierarchical view on stress signaling, where metabolites are seen as final downstream products, has recently been complemented by findings that metabolites themselves function as stress signals. We present a systematic concept of metabolic responses that are induced by environmental stresses and persist in the plant system. Such metabolic imprints may prime metabolic responses of plants for subsequent environmental stresses. We describe response types with examples of biotic and abiotic environmental stresses and suggest that plants use metabolic imprints, the metabolic changes that last beyond recovery from stress events, and priming, the imprints that function to prepare for upcoming stresses, to integrate diverse environmental stress histories. As a consequence, even genetically identical plants should be studied and understood as phenotypically plastic organisms that continuously adjust their metabolic state in response to their individually experienced local environment. To explore the occurrence and to unravel functions of metabolic imprints, we encourage researchers to extend stress studies by including detailed metabolic and stress response monitoring into extended recovery phases.

Low CO2 induces urea cycle intermediate accumulation in Arabidopsis thaliana

The non-proteinogenic amino acid ornithine links several stress response pathways. From a previous study we know that ornithine accumulates in response to low CO2. To investigate ornithine accumulation in plants, we shifted plants to either low CO2 or low light. Both conditions increased carbon limitation, but only low CO2 also increased the rate of photorespiration. Changes in metabolite profiles of light- and CO2-limited plants were quite similar. Several amino acids that are known markers of senescence accumulated strongly under both conditions. However, urea cycle intermediates respond differently between the two treatments. While the levels of both ornithine and citrulline were much higher in plants shifted to 100 ppm CO2 compared to those kept in 400 ppm CO2, their metabolite abundance did not significantly change in response to a light limitation. Furthermore, both ornithine and citrulline accumulation is independent from sugar starvation. Exogenous supplied sugar did not significantly change the accumulation of the two metabolites in low CO2-stressed plants, while the accumulation of other amino acids was reduced by about 50%. Gene expression measurements showed a reduction of the entire arginine biosynthetic pathway in response to low CO2. Genes in both proline biosynthesis and degradation were induced. Hence, proline did not accumulate in response to low CO2 like observed for many other stresses. We propose that excess of nitrogen re-fixed during photorespiration can be alternatively stored in ornithine and citrulline under low CO2 conditions. Furthermore, ornithine is converted to pyrroline-5-carboxylate by the action of δOAT.

The transcription factor FcWRKY40 of Fortunella crassifolia functions positively in salt tolerance through modulation of ion homeostasis and proline biosynthesis by directly regulating SOS2 and P5CS1 homologs

Although some WRKYs have been characterized, regulatory roles of most WRKYs remain poorly understood. Herein, we elucidated function of FcWRKY40 from Fortunella crassifolia in salt tolerance via overexpression and virus-induced gene silencing (VIGS) and unraveled its target genes. Overexpression of FcWRKY40 enhanced salt tolerance in transgenic tobacco and lemon, while silencing of FcWRKY40 increased salt susceptibility. Homolog genes of Salt Overly Sensitive 2 (SOS2) and Δ-1-pyrroline-5-carboxylate synthetase 1 (P5CS1) were dramatically up-regulated in transgenic lemon but down-regulated in VIGS line. Consistently, transgenic lemon displayed lower Na+ and higher proline concentrations, whereas the silenced line accumulated more Na+ but less proline. Treatment of transgenic lemon with 24-epi-brassinolide compromised salt tolerance, while supply of exogenous proline partially restored salt tolerance of the VIGS line. FcWRKY40 specifically binds to and activates promoters of FcSOS2 and FcP5CS1. FcWRKY40 was up-regulated by ABA and salt, and confirmed as a target of ABA-responsive element binding factor 2 (FcABF2). Moreover, salt treatment up-regulated FcABF2 and FcP5CS1, and elevated proline concentrations. Taken together, our findings demonstrate that FcWRKY40 participates in the ABA signaling pathway and as a positive regulator functions in salt tolerance by regulating genes involved in ion homeostasis and proline biosynthesis.

Transcriptomic studies reveal a key metabolic pathway contributing to a well-maintained photosynthetic system under drought stress in foxtail millet (Setaria italica L.)

Drought stress is one of the most important abiotic factors limiting crop productivity. A better understanding of the effects of drought on millet (Setaria italica L.) production, a model crop for studying drought tolerance, and the underlying molecular mechanisms responsible for drought stress responses is vital to improvement of agricultural production. In this study, we exposed the drought resistant F1 hybrid, M79, and its parental lines E1 and H1 to drought stress. Subsequent physiological analysis demonstrated that M79 showed higher photosynthetic energy conversion efficiency and drought tolerance than its parents. A transcriptomic study using leaves collected six days after drought treatment, when the soil water content was about ∼20%, identified 3066, 1895, and 2148 differentially expressed genes (DEGs) in M79, E1 and H1 compared to the respective untreated controls, respectively. Further analysis revealed 17 Gene Ontology (GO) enrichments and 14 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways in M79, including photosystem II (PSII) oxygen-evolving complex, peroxidase (POD) activity, plant hormone signal transduction, and chlorophyll biosynthesis. Co-regulation analysis suggested that these DEGs in M79 contributed to the formation of a regulatory network involving multiple biological processes and pathways including photosynthesis, signal transduction, transcriptional regulation, redox regulation, hormonal signaling, and osmotic regulation. RNA-seq analysis also showed that some photosynthesis-related DEGs were highly expressed in M79 compared to its parental lines under drought stress. These results indicate that various molecular pathways, including photosynthesis, respond to drought stress in M79, and provide abundant molecular information for further analysis of the underlying mechanism responding to this stress.

Individual and combined effects of fluoranthene, phenanthrene, mannitol and sulfuric acid on marigold (Calendula officinalis)

A study was conducted to characterize marigold stress response to polycyclic aromatic hydrocarbons (PAHs) (oxidative stress inducers) with and without sulfuric acid (S.Acid; pH 3) (acid-stress inducer), and to evaluate reactive oxygen species (ROS) scavenging activity of mannitol (Mann). Marigold (Calendula officinalis) seedlings were grown in a greenhouse and fumigated with fluoranthene (FLU), phenanthrene (PHE), Mann, and S.Acid individually and in various combinations for 40 days. Various physiological and biochemical parameters among others were analyzed using standard methods. The results revealed that fumigation of FLU induced oxidative stress to the plants via ROS generation leading to negative effects on photosynthesis at near saturating irradiance (A_max), stomatal conductance (G_s), internal carbon dioxide concentration (C_i), leaf water relations and chlorophyll pigments. Significant per cent inhibition of A_max (54%), G_s (86%) and C_i (32%), as well as per cent reductions in chlorophyll a (Chl.a) (33%), Chl.b (34%), and total chlorophyll (Tot. Chl) (48%) contents were recorded in FLU fumigated treatment in comparison to control. Combination of Mann with FLU scavenged the generated ROS and substantially lowered the oxidative stress on the plants hence all the measured parameters were not significantly different from control. PHE fumigation had varied effects on marigold plants and was not as deleterious as FLU. Combined fumigation of S.Acid with both the PAHs had significant negative effect on leaf water relations, and positive effect on fresh and turgid weight of the plants but had no effect on the other measured parameters. The lowest proline contents and highest catalase and ascorbate peroxidase activities in FLU fumigated plants further confirmed that oxidative stress was imposed via the generation of ROS. From the results, it is evident that Mann could be an efficient scavenger of ROS-generated by FLU in the marigold plants. We recommend Mann to be widely used for the protection of higher plants from FLU-generated stress in the urban areas.

Transcriptomic studies reveal a key metabolic pathway contributing to a well-maintained photosynthetic system under drought stress in foxtail millet (Setaria italica L.)

Drought stress is one of the most important abiotic factors limiting crop productivity. A better understanding of the effects of drought on millet (Setaria italica L.) production, a model crop for studying drought tolerance, and the underlying molecular mechanisms responsible for drought stress responses is vital to improvement of agricultural production. In this study, we exposed the drought resistant F₁ hybrid, M79, and its parental lines E1 and H1 to drought stress. Subsequent physiological analysis demonstrated that M79 showed higher photosynthetic energy conversion efficiency and drought tolerance than its parents. A transcriptomic study using leaves collected six days after drought treatment, when the soil water content was about ∼20%, identified 3066, 1895, and 2148 differentially expressed genes (DEGs) in M79, E1 and H1 compared to the respective untreated controls, respectively. Further analysis revealed 17 Gene Ontology (GO) enrichments and 14 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways in M79, including photosystem II (PSII) oxygen-evolving complex, peroxidase (POD) activity, plant hormone signal transduction, and chlorophyll biosynthesis. Co-regulation analysis suggested that these DEGs in M79 contributed to the formation of a regulatory network involving multiple biological processes and pathways including photosynthesis, signal transduction, transcriptional regulation, redox regulation, hormonal signaling, and osmotic regulation. RNA-seq analysis also showed that some photosynthesis-related DEGs were highly expressed in M79 compared to its parental lines under drought stress. These results indicate that various molecular pathways, including photosynthesis, respond to drought stress in M79, and provide abundant molecular information for further analysis of the underlying mechanism responding to this stress.

Artemisia dominant species succession relating to the soil moisture decrease in abandoned land of the Loess Plateau (China): comparative study of drought-adaptive characteristics

Artemisia scoparia, Artemisia sacrorum and Artemisia giraldii were three dominant Artemisia species which successive grew in the secondary succession on abandoned land of the Loess Plateau. The succession accompanied the soil moisture steady decrease with field age after their abandonment. To elucidate the relationship between the Artemisia species succession and their drought-adaptation, three dominant species and a contrastive species Artemisia annua (mesophyte), were selected to compare their drought-resistant characteristics, including morphological and anatomical traits of leaf and root. Then physiological responses were investigated in mature plants after drought treatment. The results indicated that three dominant species leaf presented drought-adaptive structures, such as bushy trichomes, transitional or isolateral leaf cells, thick cuticles and epidermal cells. However, A. annua had no leaf traits involved in drought-adaptation. In addition, A. sacrorum and A. giraldii contained large root systems, while A. scoparia and A. annua utilized succulent roots. The physiological responses to drought suggested that A. giraldii had strong regulation in water using strategy, growth, as well as superoxide dismutase and catalase activity. A. sacrorum and A. giraldii could maintain high ascorbate peroxidase activity and malondialdehyde content, while A. scoparia and A. giraldii presented higher peroxidase activity, ascorbate and soluble sugar content. A. annua exhibited high proline and carotenoid contents under drought. The drought-resistant of the four Artemisia species presented the order of A. giraldii > A. sacrorum > A. scoparia > A. annua, which was consistent with their succession on abandoned land.

Water deficit stress-induced changes in carbon and nitrogen partitioning in Chenopodium quinoa Willd

Water deficit stress followed by re-watering during grain filling resulted in the induction of the ornithine pathway and in changes in Quinoa grain quality. The genetic diversity of Chenopodium quinoa Willd. (Quinoa) is accompanied by an outstanding environmental adaptability and high nutritional properties of the grains. However, little is known about the biochemical and physiological mechanisms associated with the abiotic stress tolerance of Quinoa. Here, we characterized carbon and nitrogen metabolic changes in Quinoa leaves and grains in response to water deficit stress analyzing their impact on the grain quality of two lowland ecotypes (Faro and BO78). Differences in the stress recovery response were found between genotypes including changes in the activity of nitrogen assimilation-associated enzymes that resulted in differences in grain quality. Both genotypes showed a common strategy to overcome water stress including the stress-induced synthesis of reactive oxygen species scavengers and osmolytes. Particularly, water deficit stress induced the stimulation of the ornithine and raffinose pathways. Our results would suggest that the regulation of C- and N partitioning in Quinoa during grain filling could be used for the improvement of the grain quality without altering grain yields.

Genotypic Variation in Growth and Physiological Response to Drought Stress and Re-Watering Reveals the Critical Role of Recovery in Drought Adaptation in Maize Seedlings

Non-irrigated crops in temperate climates and irrigated crops in arid climates are subjected to continuous cycles of water stress and re-watering. Thus, fast and efficient recovery from water stress may be among the key determinants of plant drought adaptation. The present study was designed to comparatively analyze the roles of drought resistance and drought recovery in drought adaptation and to investigate the physiological basis of genotypic variation in drought adaptation in maize (Zea mays) seedlings. As the seedlings behavior in growth associate with yield under drought, it could partly reflect the potential of drought adaptability. Growth and physiological responses to progressive drought stress and recovery were observed in seedlings of 10 maize lines. The results showed that drought adaptability is closely related to drought recovery (r = 0.714(**)), but not to drought resistance (r = 0.332). Drought induced decreases in leaf water content, water potential, osmotic potential, gas exchange parameters, chlorophyll content, Fv/Fm and nitrogen content, and increased H2O2 accumulation and lipid peroxidation. After recovery, most of these physiological parameters rapidly returned to normal levels. The physiological responses varied between lines. Further correlation analysis indicated that the physiological bases of drought resistance and drought recovery are definitely different, and that maintaining higher chlorophyll content (r = 0.874(***)) and Fv/Fm (r = 0.626(*)) under drought stress contributes to drought recovery. Our results suggest that both drought resistance and recovery are key determinants of plant drought adaptation, and that drought recovery may play a more important role than previously thought. In addition, leaf water potential, chlorophyll content and Fv/Fm could be used as efficient reference indicators in the selection of drought-adaptive genotypes.