PEG-Induced Osmotic Stress Alters Root Morphology and Root Hair Traits in Wheat Genotypes

Drought affects Fe deficiency-induced responses in a purple durum wheat (Triticum turgidum subsp. durum) genotype

Iron (Fe) is essential for plants and humans, with over 2 billion people suffering deficiency disorders because most plant foods, including cereals, are low in Fe. Durum wheat, a staple crop in Mediterranean regions, is facing increased droughts, which reduce plant yield and ability to acquire and use Fe. Therefore, understanding mechanisms underlying Fe acquisition and accumulation in durum wheat under drought is essential for both agronomic and nutritional purposes. Here, a durum wheat (Triticum turgidum subsp. durum) genotype with a purple grain pericarp was grown hydroponically under adequate (80 μM) or limited (10 μM) Fe, with or without water stress (induced with 10% PEG 6000) for 6 days. Fe accumulation decreased under Fe deficiency and drought, with the highest phytosiderophore (PS) release in Fe-deficient plants. Interestingly, despite adequate Fe availability, drought inhibited Fe accumulation in roots. This response was accompanied by increased release of PS from roots, although the increase was less than that observed with single or combined Fe deficiency. Both TdIRT1 and TdYS15 were upregulated by Fe deficiency but downregulated by drought and the combined stress. Drought stress and Fe deficiency led to increased ABA production, being 250-fold higher with respect to controls. TdIRT1 downregulation in plants exposed to the combined stress suggests a trade-off between water and Fe stress responses. Our findings demonstrate that the response to combined stress differs from, and is rarely additive to, the response to a single stressor, reinforcing the complexity of plant adaptation to combined environmental stresses.

CRISPR-mediated mutation of cytokinin signaling genes (SlHP2 and SlHP3) in tomato: Morphological, physiological, and molecular characterization

Synergistic and antagonistic relationships between cytokinins and other plant growth regulators are important in response to changing environmental conditions. Our study aimed to determine the functions of SlHP2 and SlHP3, two members of cytokinin signaling in tomato, in drought stress response using CRISPR/Cas9-mediated mutagenesis. Ten distinct genome-edited lines were generated via Agrobacterium tumefaciens-mediated gene transfer and confirmed through Sanger sequencing. Stress experiments were conducted with two of these lines (slhp2,3-10 and slhp2,3-11), which harbored homozygous mutations in both genes. The responses of two lines carrying homozygous mutations in both genes under polyethylene glycol (PEG)-induced stress were examined using morphological, physiological, biochemical, and molecular methods. The genome-edited lines demonstrated enhanced water retention, reduced stomatal density, and less oxidative damage compared to the wild-type plants under PEG-induced stress. Moreover, the slhp2,3 double mutant plants exhibited improved root growth, showcasing their superior drought tolerance over wild-type plants by accessing deeper water sources and maintaining hydration in water-limited environments. To investigate the involvement of cytokinin signaling regulators and genes associated with stomatal formation and differentiation, the expression of genes (Speechless [SPCH], FAMA, MUTE, TMM, HB25, HB31, RR6, RR7, and Solyc02g080860) was assessed. The results revealed that all regulators were downregulated, with SPCH, TMM, RR7, and RR6 showing significant reductions under PEG-induced stress. These results emphasize the promise of utilizing CRISPR/Cas9 to target cytokinin signaling pathways, enhancing drought tolerance in tomatoes through improvements in water retention and root growth, along with a reduction in stomatal density and malondialdehyde content.

Effects of drought and salt stress on the root phenotype of wheat seedlings and underlying gene expression analysis

In our previous study, three TaPSK genes highly expressed in the roots of wheat were screened. To explore the effects of adverse stresses on the wheat root phenotype and the expression of TaPSK3, TaPSK9 and TaPSK10, we measured the phenotypic parameters of the JM22 root system at the seedling stage after treatment with different concentrations of NaCl and PEG6000. Additionally, the relative expression levels of TaPSK3, TaPSK9, and TaPSK10 were analyzed via RT-qPCR within 72 h of treatment with 150 mM NaCl and 30% PEG6000. The results revealed that drought and salt stress significantly inhibited phenotypic parameters such as total root length, root surface area, root biomass distribution estimation and root tip number in wheat. Notably, salt stress causes wheat roots to germinate more root hairs. The expression of TaPSK3 did not change significantly during salt stress but was upregulated approximately five-fold at 12 h of drought stress. The gene expression levels of TaPSK9 and TaPSK10 were upregulated to varying degrees but gradually returned to normal at 72 h. These results show that when wheat encounters stresses, the expression of TaPSK genes is upregulated to promote root growth and ensure the normal growth and development of plants. This study provides data and theoretical support for further study of TaPSK gene function and cultivation of high-quality wheat plants with strong stress resistance.

PGPB Isolated from Drought-Tolerant Plants Help Wheat Plants to Overcome Osmotic Stress

The aim of this research was to study the effect of plant-growth-promoting bacteria (PGPB) isolated from the drought-tolerant plants camel thorn (Alhagi pseudoalhagi (M.Bieb.) Fisch) and white pigweed (Chenopodium album L.) on wheat (Triticum aestivum L.) plants cv. Lenigradskaya 6, growing under hydroponic conditions and osmotic stress (generated by 12% polyethylene glycol-6000 (PEG)). Based on the assumption that plants create a unique microbiome that helps them overcome various stresses, we hypothesized that bacteria isolated from drought-tolerant plants may assist cultivated wheat plants in coping with drought stress. PGPB were isolated from seeds and leaves of plants and identified as Bacillus spp. (strains Cap 07D, Cap 09D, and App 11D); Paenibacillus sp. (Cap 286); and Arthrobacter sp. (Cap 03D). All bacteria produced different phytohormones such as indole acetic acid (IAA), abscisic acid (ABA), and gibberellic acid (GAS3) and were capable of stimulating wheat growth under normal and osmotic stress conditions. All PGPB reduced the malondialdehyde (MDA) content, increased the total chlorophyll content by increasing chlorophyll a, and modulated wheat hormone homeostasis and CAT and POX activities under osmotic conditions. Selected strains can be promising candidates for the mitigating of the drought stress of wheat plants.

Genotypic Variability in Root Morphology in a Diverse Wheat Genotypes Under Drought and Low Phosphorus Stress

Screening genotypes with optimal root traits presents a promising breeding strategy for enhancing adaptability to abiotic stresses and improving resource use efficiency. This study evaluated root traits of 100 winter wheat genotypes under four treatments: control (C), low phosphorus (LP), PEG-induced drought (D), and a combination of LP and drought (DLP), using a semi-hydroponic phenotyping platform. Significant variations in root traits were observed 65 days after transplanting, with over 80% of traits being significantly affected by drought, phosphorus, or their interactions. Biomass and phosphorus content decreased under LP and drought, while root length and diameter in deeper layers increased, especially under drought stress. Combined stress led to the most severe reductions in biomass, P-content, and leaf number. Phosphorus acquisition efficiency was positively correlated with root length but inversely related to stress tolerance. High heritability traits, such as root number, root length, maximum root depth, leaf number, and biomass, hold potential for breeding programs focused on environmental adaptation, resource efficiency, and yield improvement. The substantial genotypic variation in root morphology under stress conditions highlights the potential for breeding stress-resilient wheat genotypes. This finding lays a foundation for wheat-breeding initiatives aimed at developing genotypes better suited to prevailing environmental conditions.

PEG treatment is unsuitable to study root related traits as it alters root anatomy in barley (Hordeum vulgare L.)

BACKGROUND

The frequency and severity of abiotic stress events, especially drought, are increasing due to climate change. The plant root is the most important organ for water uptake and the first to be affected by water limitation. It is therefore becoming increasingly important to include root traits in studies on drought stress tolerance. However, phenotyping under field conditions remains a challenging task. In this study, plants were grown in a hydroponic system with polyethylene glycol as an osmotic stressor and in sand pots to examine the root system of eleven spring barley genotypes. The root anatomy of two genotypes with different response to drought was investigated microscopically.

RESULTS

Root diameter increased significantly (p < 0.05) under polyethylene glycol treatment by 54% but decreased significantly (p < 0.05) by 12% under drought stress in sand pots. Polyethylene glycol treatment increased root tip diameter (51%) and reduced diameter of the elongation zone (14%) compared to the control. Under drought stress, shoot mass of plants grown in sand pots showed a higher correlation (r = 0.30) with the shoot mass under field condition than polyethylene glycol treated plants (r = -0.22).

CONCLUSION

These results indicate that barley roots take up polyethylene glycol by the root tip and polyethylene glycol prevents further water uptake. Polyethylene glycol-triggered osmotic stress is therefore unsuitable for investigating root morphology traits in barley. Root architecture of roots grown in sand pots is more comparable to roots grown under field conditions.

A detailed study on genetic diversity, antioxidant machinery, and expression profile of drought-responsive genes in rice genotypes exposed to artificial osmotic stress

Seasonal variations in rainfall patterns, particularly during sowing, early growing season, and flowering, drastically affect rice production in northeastern India. However, sensitivity to drought stress is genotype-specific. Since 80% of the land in this region is used for rice production, it is crucial to understand how they have adapted to water stress. This study evaluated 112 rice genotypes grown in NE India for seed germination percentage and seedling development under PEG-mediated drought stress. Among the rice genotype, Sahbhagi dhan, RCPL-1-82, Bhalum-3 and RCPL-1-128 showed drought-tolerant traits, while Ketaki Joha, Chakhao, Chandan, RCPL-1-185 and IR-64 were the most drought-sensitive rice genotypes. Drought-tolerant rice also showed significantly higher seed germination potential, proline content, antioxidant activity and expression of drought-responsive genes than drought-sensitive rice genotypes. A similar expression pattern of genes was also observed in the rice genotype treated with a 50% water deficit in pot culture. In addition, drought stress reduced the pollen fertility and yield per plant in sensitive rice genotypes. Molecular markers associated with drought stress were also used to characterize genetic diversity among the rice genotypes studied.

An artificial intelligence-integrated analysis of the effect of drought stress on root traits of "modern" and "ancient" wheat varieties

Due to drought stress, durum wheat production in the Mediterranean basin will be severely affected in the coming years. Durum wheat cultivation relies on a few genetically uniform "modern" varieties, more productive but less tolerant to stresses, and "traditional" varieties, still representing a source of genetic biodiversity for drought tolerance. Root architecture plasticity is crucial for plant adaptation to drought stress and the relationship linking root structures to drought is complex and still largely under-explored. In this study, we examined the effect of drought stress on the roots' characteristics of the "traditional" Saragolla cultivar and the "modern" Svevo. By means of "SmartRoot" software, we demonstrated that drought stress affected primary and lateral roots as well as root hair at different extents in Saragolla and Svevo cultivars. Indeed, we observed that under drought stress Saragolla possibly revamped its root architecture, by significantly increasing the length of lateral roots, and the length/density of root hairs compared to the Svevo cultivar. Scanning Electron Microscopy analysis of root anatomical traits demonstrated that under drought stress a greater stele area and an increase of the xylem lumen size vessel occurred in Saragolla, indicating that the Saragolla variety had a more efficient adaptive response to osmotic stress than the Svevo. Furthermore, for the analysis of root structural data, Artificial Intelligence (AI) algorithms have been used: Their application allowed to predict from root structural traits modified by the osmotic stress the type of cultivar observed and to infer the relationship stress-cultivar type, thus demonstrating that root structural traits are clear and incontrovertible indicators of the higher tolerance to osmotic stress of the Saragolla cultivar. Finally, to obtain an integrated view of root morphogenesis, phytohormone levels were investigated. According to the phenotypic effects, under drought stress,a larger increase in IAA and ABA levels, as well as a more pronounced reduction in GA levels occurred in Saragolla as compared to Svevo. In conclusion, these results show that the root growth and hormonal profile of Saragolla are less affected by osmotic stress than those of Svevo, demonstrating the great potential of ancient varieties as reservoirs of genetic variability for improving crop responses to environmental stresses.

Spermine induced endogenous signal ameliorates osmotic stress in Lens culinaris

The present study evaluates the alleviation of polyethylene glycol (PEG) mediated osmotic stress by exogenous spermine (SP) application on seeds of Lens culinaris. Seeds were soaked overnight with SP (0.05 M) and PEG (10%) separately. Third set was prepared by combined treatment with SP (0.05 M) and PEG (10%). Further, various physiological parameters, defense enzymes, phenol, flavonoid, nitric oxide (NO), proline content, chromosomal abnormality studies etc. was conducted after 5 days of incubation. PEG application significantly hampered the seed germination, root length, shoot length, relative water content and vigour index. Application of PEG induced electrolytic leakage in root cells. PEG application also significantly reduced the activities of different defense parameters viz. peroxidase, polyphenol oxidase, phenylalanine ammonia lyase and β-1,3 glucanase, total phenol and flavonoid accumulation over control. Reactive oxygen species, lipid peroxidation, cell death was found significantly high in PEG treated sets. However, NO level has been significantly decreased by PEG treatment. Cytological studies showed reduced mitotic index and highest abnormalities under osmotic stress. Contrary to that, application of SP either alone or in combination with PEG showed improved responses of aforesaid defense parameters compared to control and solely PEG treated sets. Interestingly, cytological abnormalities were also reduced in SP treated roots. Overall, these results suggests that SP application on seeds reduced the PEG induced damage and intricately improved the defense mechanisms which might help to fight against oxidative stress.

Assessment of halotolerant bacterial and fungal consortia for augmentation of wheat in saline soils

Adaptations of green technologies to counter abiotic stress, including salinity for crops like wheat by using halotolerant microbes, is a promising approach. The current study investigated 17 salt-affected agroecological zones from the Punjab and Sindh provinces of Pakistan to explore the potential of indigenous microbial flora, with their multiple biochemical characteristics in addition to plant growth promoting (PGP) traits, for enhanced wheat production in saline areas. Initially, 297 isolated pure bacterial colonies were screened for salt tolerance, biochemical, and PGP traits. Three bacterial strains belonging to Pantoea spp. and Erwinia rhaphontici with possession of multiple characteristics were selected for the development of the halotolerant bacterial consortium. Inoculation of two local wheat varieties, Faisalabad 2008 and Galaxy 2013, with the consortium for in vitro seed germination assay and sand microcosm experiments exhibited significant improvement of selected plant growth parameters like germination percentage and root structure. Two previously reported PGP fungal strains of Trichoderma harzianum and T. viridae were also used as fungal consortium separately for pot experiments and field trials. The pot experiments exhibited a positive correlation of consortia with metabolic viz. catalase, peroxidase, and proline and agronomical parameters including shoot length, dry weight, number of spikes, spike length, and 100 grain weight. To evaluate their performance under natural environmental conditions, field trials were conducted at three salt-affected sites. Agronomical attributes including days of flowering and maturity, flag leaf weight, length and width, shoot length, number of spikes, spike length, spike weight, number of seeds spike-1, 1,000 grain weight, and plot yield indicated the efficiency of these microbes to enhance wheat growth. Concisely, the bacterial consortium showed better performance and Faisalabad 2008 was a more resistant variety as compared to Galaxy 2013. Initial promising results indicate that further extensive research on indigenous microbes might lead to the development of Pakistan's first saline-specific biofertilizers and sustainable eco-friendly agriculture practices.

Crop root system plasticity for improved yields in saline soils

Crop yields must increase to meet the demands of a growing world population. Soil salinization is increasing due to the impacts of climate change, reducing the area of arable land for crop production. Plant root systems are plastic, and their architecture can be modulated to (1) acquire nutrients and water for growth, and (2) respond to hostile soil environments. Saline soils inhibit primary root growth and alter root system architecture (RSA) of crop plants. In this review, we explore how crop root systems respond and adapt to salinity, focusing predominately on the staple cereal crops wheat, maize, rice, and barley, that all play a major role in global food security. Cereal crops are classified as glycophytes (salt-sensitive) however salt-tolerance can differ both between species and within a species. In the past, due to the inherent difficulties associated with visualising and measuring root traits, crop breeding strategies have tended to focus on optimising shoot traits. High-resolution phenotyping techniques now make it possible to visualise and measure root traits in soil systems. A steep, deep and cheap root ideotype has been proposed for water and nitrogen capture. Changes in RSA can be an adaptive strategy to avoid saline soils whilst optimising nutrient and water acquisition. In this review we propose a new model for designing crops with a salt-tolerant root ideotype. The proposed root ideotype would exhibit root plasticity to adapt to saline soils, root anatomical changes to conserve energy and restrict sodium (Na⁺) uptake, and transport mechanisms to reduce the amount of Na⁺ transported to leaves. In the future, combining high-resolution root phenotyping with advances in crop genetics will allow us to uncover root traits in complex crop species such as wheat, that can be incorporated into crop breeding programs for yield stability in saline soils.

Screening of Triticum turgidum genotypes for tolerance to drought stress

Drought is one of the major abiotic stresses leading to reduced yields and economic losses. Effective germplasm screening for drought tolerance particularly under managed water-deficit conditions is an effective way of selecting materials for advanced breeding programs. Here, 37 Triticum turgidum genotypes, including landraces, ancient and modern genotypes, along with 2 tritordeum cultivars, were subjected to water-deficit stress through the application of 10% (w/v) PEG 6000 and to re-watering treatment in controlled environment, and at the end of each treatment, several physiological and morphological traits were investigated. Our results revealed large variation in shoot and root fresh weight, proline, chlorophyll, and MDA concentration, and also in root morphological traits across the 37 genotypes. The hierarchical clustering of the physiological and morphological traits led to the identification of tolerant and sensitive genotypes to water-deficit stress and also reveals those genotypes characterized by deep-rooting and shallow-rooting systems. By integrating both datasets, three outstanding genotypes, namely Karim, Svems 20, and Svems 18 were identified as the most tolerant genotypes with deep-rooting system. On the other hand, Iride and Bulel tritordeum, were introduced as the most sensitive genotypes with shallow-rooting system.

Responses of root system architecture to water stress at multiple levels: A meta-analysis of trials under controlled conditions

Plants are exposed to increasingly severe drought events and roots play vital roles in maintaining plant survival, growth, and reproduction. A large body of literature has investigated the adaptive responses of root traits in various plants to water stress and these studies have been reviewed in certain groups of plant species at a certain scale. Nevertheless, these responses have not been synthesized at multiple levels. This paper screened over 2000 literatures for studies of typical root traits including root growth angle, root depth, root length, root diameter, root dry weight, root-to-shoot ratio, root hair length and density and integrates their drought responses at genetic and morphological scales. The genes, quantitative trait loci (QTLs) and hormones that are involved in the regulation of drought response of the root traits were summarized. We then statistically analyzed the drought responses of root traits and discussed the underlying mechanisms. Moreover, we highlighted the drought response of 1-D and 2-D root length density (RLD) distribution in the soil profile. This paper will provide a framework for an integrated understanding of root adaptive responses to water deficit at multiple scales and such insights may provide a basis for selection and breeding of drought tolerant crop lines.

Plant CDKs-Driving the Cell Cycle through Climate Change

In a growing population, producing enough food has become a challenge in the face of the dramatic increase in climate change. Plants, during their evolution as sessile organisms, developed countless mechanisms to better adapt to the environment and its fluctuations. One important way is through the plasticity of their body and their forms, which are modulated during plant growth by accurate control of cell divisions. A family of serine/threonine kinases called cyclin-dependent kinases (CDK) is a key regulator of cell divisions by controlling cell cycle progression. In this review, we compile information on the primary response of plants in the regulation of the cell cycle in response to environmental stresses and show how the cell cycle proteins (mainly the cyclin-dependent kinases) involved in this regulation can act as components of environmental response signaling cascades, triggering adaptive responses to drive the cycle through climate fluctuations. Understanding the roles of CDKs and their regulators in the face of adversity may be crucial to meeting the challenge of increasing agricultural productivity in a new climate.

Time Course of Root Axis Elongation and Lateral Root Formation in Perennial Ryegrass (Lolium perenne L.)

Grasses have a segmental morphology. Compared to leaf development, data on root development at the phytomer level are scarce. Leaf appearance interval was recorded over time to allow inference about the age of segmental sites that later form roots. Hydroponically grown Lolium perenne cv. Aberdart tillers were studied in both spring and autumn in increasing and decreasing day length conditions, respectively, and dissected to define the development status of roots of known age on successive phytomers basipetally on the tiller axis. Over a 90-day observation period spring and autumn tillers produced 10.4 and 18.1 root bearing phytomers (Pr), respectively. Four stages of root development were identified: (0) main axis elongation (~0–10 days), (1) primary branching (~10–18 days), (2) secondary branching (~18–25 days), and (3) tertiary and quaternary branching without further increase in root dry weight. The individual spring roots achieved significantly greater dry weight (35%) than autumn roots, and a mechanism for seasonal shift in substrate supply to roots is proposed. Our data define a root turnover pattern likely also occurring in field swards and provide insight for modelling the turnover of grass root systems for developing nutrient efficient or stress tolerant ryegrass swards.