Genetic and physiological controls of growth under water deficit

Role of biotin carboxyl carrier protein subunit 2 (BCCP2) in resistance to multiple stresses in Arabidopsis thaliana

Abiotic stresses, including drought, salinity, and temperature extremes, are serious constraints to plant growth and agricultural development. These stresses that plants face in nature are often multiple and complex. Biotin carboxyl carrier protein subunit 2 (BCCP2) is one of the two subunits of biotin carboxyl carrier protein, which is a functional subunit of acetyl coenzyme A carboxylase, primarily studied for its role in fatty acid synthesis. In this study, we identified the expression pattern of AtBCCP2 under various stress conditions, including 4 mM NaHCO₃, 2 mM Na₂CO₃, 150 mM NaCl, 300 mM D-mannitol, 100 μM ABA, 5 mM H₂O₂, 4 °C, and 37 °C. It was determined that AtBCCP2 is positively regulated by NaHCO₃, Na₂CO₃, NaCl, and ABA, but negatively regulated by D-mannitol. Phenotypic experiment confirmed that the AtBCCP2 transgenic overexpression plants exhibited increased resistance to NaHCO₃, Na₂CO₃, NaCl, and ABA stresses, but more sensitive to drought stress simulated by D-mannitol. In contrast, mutant plants showed the opposite phenotypes. Additionally, AtBCCP2 transgenic overexpression plants demonstrated stronger antioxidant activity and lower MDA content under stresses such as NaHCO₃, Na₂CO₃, NaCl, and ABA, in contrast to the mutant plants. In response to D-mannitol simulated drought stress, AtBCCP2 transgenic overexpression plants showed lower antioxidant activity and higher MDA content, while mutant plants exhibited the opposite trend. In conclusion, this study provides a theoretical basis for understanding the role of AtBCCP2 in response to multiple stresses and contributes a new gene to the pool of those involved in abiotic stress responses.

Tubulin participates in establishing protoxylem vessel reinforcement patterns and hydraulic conductivity in maize

Water transportation to developing tissues relies on the structure and function of plant xylem cells. Plant microtubules govern the direction of cellulose microfibrils and guide secondary cell wall formation and morphogenesis. However, the relevance of microtubule-determined xylem wall thickening patterns in plant hydraulic conductivity remains unclear. In the present study, we identified a maize (Zea mays) semi-dominant mutant, designated drought-overly-sensitive1 (ZmDos1), the upper leaves of which wilted even when exposed to well-watered conditions during growth; the wilting phenotype was aggravated by increased temperatures and decreased humidity. Protoxylem vessels in the stem and leaves of the mutant showed altered thickening patterns of the secondary cell wall (from annular to spiral), decreased inner diameters, and limited water transport efficiency. The causal mutation for this phenotype was found to be a G-to-A mutation in the maize gene α-tubulin4, resulting in a single amino acid substitution at position 196 (E196K). Ectopic expression of the mutant α-tubulin4 in Arabidopsis (Arabidopsis thaliana) changed the orientation of microtubule arrays, suggesting a determinant role of this gene in microtubule assembly and secondary cell wall thickening. Our findings suggest that the spiral wall thickenings triggered by the α-tubulin mutation are stretched during organ elongation, causing a smaller inner diameter of the protoxylem vessels and affecting water transport in maize. This study underscores the importance of tubulin-mediated protoxylem wall thickening in regulating plant hydraulics, improves our understanding of the relationships between protoxylem structural features and functions, and offers candidate genes for the genetic enhancement of maize.

Growth kinetics, spatialization and quality of potato tubers monitored in situ by MRI - long-term effects of water stress

Understanding the potato tuber development and effects of drought at key stages of sensitivity on yield is crucial, particularly when considering the increasing incidence of drought due to climate change. So far, few studies addressed the time course of tuber growth in soil, mainly due to difficulties in accessing underground plant organs in a non-destructive manner. This study aims to understand the tuber growth and quality and the complex long-term effects of realistic water stress on potato tuber yield. MRI was used to monitor the growth kinetics and spatialization of individual tubers in situ and the evolution of internal defects throughout the development period. The intermittent drought applied to plants reduced tuber yield by reducing tuber growth and increasing the number of aborted tubers. The reduction in the size of tubers depended on the vertical position of the tubers in the soil, indicating water exchanges between tubers and the mother plant during leaf dehydration events. The final size of tubers was linked with the growth rate at specific developmental periods. For plants experiencing stress, this corresponded to the days following rewatering, suggesting tuber growth plasticity. All internal defects occurred in large tubers and within a short time span immediately following a period of rapid growth of perimedullary tissues, probably due to high nutrient requirements. To conclude, the non-destructive 3D imaging by MRI allowed us to quantify and better understand the kinetics and spatialization of tuber growth and the appearance of internal defects under different soil water conditions.

Comparative differences in maintaining membrane fluidity and remodeling cell wall between Glycine soja and Glycine max leaves under drought

Water shortage is one of the most important environmental factors limiting crop yield. In this study, we used wild soybean (Glycine soja Sieb. et Zucc.) and soybean (Glycinemax (L.) Merr.) seedlings as experimental materials, simulated drought stress using soil gravimetry, measured growth and physiological parameters, and analyzed differentially expressed genes and metabolites in the leaves of seedling by integrated transcriptomics and metabolomics techniques. The results indicate that under water deficit, Glycine soja maintained stable photosynthate by accumulating Mg2+, Fe3+, Mn2+, Zn2+ and B3+, and improved water absorption by increasing root growth. Notably, Glycine soja enhanced linoleic acid metabolism and plasma membrane intrinsic protein (PIP1) gene expression to maintain membrane fluidity, and increased pentose, glucuronate and galactose metabolism and thaumatin protein genes expression to remodel the cell wall, thereby increasing water-absorption to better tolerate to drought stress. In addition, it was found that secondary phenolic metabolism, such as phenylpropane biosynthesis, flavonoid biosynthesis and ascobate and aldarate metabolism were weakened, resulting in the collapse of the antioxidant system, which was the main reason for the sensitivity of Glycine max to drought stress. These results provide new insights into plant adaptation to water deficit and offer a theoretical basis for breeding soybean varieties with drought tolerance.

Eco-physiology of maize crops under combined stresses

The yield of maize (Zea mays L.) crops depends on their ability to intercept sunlight throughout the growing cycle, transform this energy into biomass and allocate it to the kernels. Abiotic stresses affect these eco-physiological determinants, reducing crop grain yield below the potential of each environment. Here we analyse the impact of combined abiotic stresses, such as water restriction and nitrogen deficiency or water restriction and elevated temperatures. Crop yield depends on the product of kernel yield per plant and the number of plants per unit soil area, but increasing plant population density imposes a crowding stress that reduces yield per plant, even within the range that maximises crop yield per unit soil area. Therefore, we also analyse the impact of abiotic stresses under different plant densities. We show that the magnitude of the detrimental effects of two combined stresses on field-grown plants can be lower, similar or higher than the sum of the individual stresses. These patterns depend on the timing and intensity of each one of the combined stresses and on the effects of one of the stresses on the status of the resource whose limitation causes the other. The analysis of the eco-physiological determinants of crop yield is useful to guide and prioritise the rapidly progressing studies aimed at understanding the molecular mechanisms underlying plant responses to combined stresses.

Comparison of Growth and Physiological Effects of Soil Moisture Regime on Plantago maritima Plants from Geographically Isolated Sites on the Eastern Coast of the Baltic Sea

The aim of the present study was to evaluate the morphological and physiological responses of P. maritima plants from five geographically isolated sites growing in habitats with different conditions to different substrate moisture levels in controlled conditions. Plants were produced from seed and cultivated in a greenhouse at four relatively constant soil moisture regimes: at 25, 50, and 75% soil water content and in soil flooded 3 cm above the surface (80% F). The two morphological traits that varied most strikingly among P. maritima accessions were the number of flower stalks and the number of leaves. Only plants from two accessions uniformly produced generative structures, and allocation to flowering was suppressed by both low moisture and flooding. Optimum shoot biomass accumulation for all accessions was at 50 and 75% soil moisture. The Performance Index Total was the most sensitive among the measured photosynthesis-related parameters, and it tended to decrease with an increase in soil water content for all P. maritima accessions. The initial hypothesis-that plants from relatively dry habitats will have a higher tolerance against low soil water levels, but plants from relatively wet habitats will have a higher tolerance against waterlogged or flooded soil-was not proven. The existence of three ecotypes of P. maritima within the five accessions from geographically isolated subpopulations on the eastern coast of the Baltic Sea at the level of morphological responses to soil water content can be proposed. P. maritima plants can be characterized as extremely tolerant to soil waterlogging and highly tolerant to soil flooding and low soil water content.

NtERF283 positively regulates water deficit tolerance in tobacco (Nicotianatabacum L.) by enhancing antioxidant capacity

Ethylene responsive factor (ERF) is a plant-specific transcription factor that plays a pivotal regulatory role in various stress responses. Although the genome of tobacco harbors 375 ER F genes, the functional roles of the majority of these genes remain unknown. Expression pattern analysis revealed that NtERF283 was induced by water deficit and salt stresses and mainly expressed in the roots and leaves. Subcellular localization and transcriptional activity assays confirmed that NtERF283 was localized in the nucleus and exhibited transcriptional activity. In comparison to the wild-type (WT), the NtERF283-overexpressing transgenic plants (OE) exhibited enhanced water deficit tolerance, whereas the knockout mutant erf283 displayed contrasting phenotypes. Transcriptional analysis demonstrated that several oxidative stress response genes were significantly altered in OE plants under water deficit conditions. 3,3'-diaminobenzidine (DAB) and nitroblue tetrazolium (NBT) staining showed that erf283 accumulated a higher level of reactive oxygen species (ROS) compared to the WT under water deficit conditions. Conversely, OE plants displayed the least amount of ROS accumulation. Furthermore, the activities of POD and SOD were higher in OE plants and lower in erf283, suggesting that NtERF283 enhanced the capacity to effectively eliminate ROS, consequently enhancing water deficit tolerance in tobacco. These findings strongly indicate the significance of NtERF283 in promoting tobacco water deficit tolerance through the activation of the antioxidant system.

Plasticity QTLs specifically contribute to the genotype × water availability interaction in maize

KEY MESSAGE

Multi-trial genome wide association study of plasticity indices allow to detect QTLs specifically involved in the genotype x water availability interaction. Concerns regarding high maize yield losses due to increasing occurrences of drought events are growing, and breeders are still looking for molecular markers for drought tolerance. However, the genetic determinism of traits in response to drought is highly complex and identification of causal regions is a tremendous task. Here, we exploit the phenotypic data obtained from four trials carried out on a phenotyping platform, where a diversity panel of 254 maize hybrids was grown under well-watered and water deficit conditions, to investigate the genetic bases of the drought response in maize. To dissociate drought effect from other environmental factors, we performed multi-trial genome-wide association study on well-watered and water deficit phenotypic means, and on phenotypic plasticity indices computed from measurements made for six ecophysiological traits. We identify 102 QTLs and 40 plasticity QTLs. Most of them were new compared to those obtained from a previous study on the same dataset. Our results show that plasticity QTLs cover genetic regions not identified by QTLs. Furthermore, for all ecophysiological traits, except one, plasticity QTLs are specifically involved in the genotype by water availability interaction, for which they explain between 60 and 100% of the variance. Altogether, QTLs and plasticity QTLs captured more than 75% of the genotype by water availability interaction variance, and allowed to find new genetic regions. Overall, our results demonstrate the importance of considering phenotypic plasticity to decipher the genetic architecture of trait response to stress.

Robotized indoor phenotyping allows genomic prediction of adaptive traits in the field

Breeding for resilience to climate change requires considering adaptive traits such as plant architecture, stomatal conductance and growth, beyond the current selection for yield. Robotized indoor phenotyping allows measuring such traits at high throughput for speed breeding, but is often considered as non-relevant for field conditions. Here, we show that maize adaptive traits can be inferred in different fields, based on genotypic values obtained indoor and on environmental conditions in each considered field. The modelling of environmental effects allows translation from indoor to fields, but also from one field to another field. Furthermore, genotypic values of considered traits match between indoor and field conditions. Genomic prediction results in adequate ranking of genotypes for the tested traits, although with lesser precision for elite varieties presenting reduced phenotypic variability. Hence, it distinguishes genotypes with high or low values for adaptive traits, conferring either spender or conservative strategies for water use under future climates.

Water stress and exogenous carnitine on growth and essential oil profile of Eryngium foetidum L

Water stress influences plant growth and metabolism. Carnitine, an amino acid involved in lipid metabolism, has been related to responses of plants to abiotic stresses, also modulating their metabolites. Culantro (Eryngium foetidum L.) is a perennial herb, rich in essential oils, native to Latin America, commonly used due to its culinary and medicinal properties. Here, we investigated the effect of exogenous carnitine on morphophysiology and the essential oil profile of culantro plants under water stress. For this, plants were grown under three water conditions: well-watered, drought stress, and re-watered; and sprayed with exogenous carnitine (100 µM) or water (control). Culantro growth was impaired by drought and enhanced by re-watering. Carnitine, in turn, did not reverse drought effects on growth, and impaired the growth of re-watered plants, also improving photosynthetic pigment content. Water conditions and carnitine application changed the essential oil profile of the plants. Drought and re-watering improved the production of eryngial, which was even increased with exogenous carnitine in re-watered plants. In addition, hydroquinone was only produced with the combination of re-watering and carnitine application. The application of exogenous carnitine can be a strategy to induce the production of essential oil compounds with cosmetic and pharmaceutical importance in culantro.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03757-y.

Water deficit stress changes in physiological, biochemical and antioxidant characteristics of anise (Pimpinella anisum L.)

This study was designed to evaluate the impact of water deficit stress on the seed yield and its components, physiological functions, fatty acid content and compositions, essential oil (EO) content and compositions, phenolic acids and flavonoids amounts, and antioxidant activities of anise seeds. Plants evaluations were performed under well-watered (WW), moderate water deficit stressed (MWDS), and severe water deficit stressed (SWDS). The results revealed that SWDS significantly reduced seed yield, branch number per plant, seed number, umbel number, and thousand seed weight. Water deficit stress also caused a decrease in chlorophyll content, relative water content, quantum efficiency of photosystem II, and cell membrane stability, while increasing leaf temperature. The analysis of fatty acid composition indicated that petroselinic acid was the main fatty acid and its percentage increased by 8.75% and 14.60% under MWDS and SWDS, respectively. Furthermore, MWDS increased the EO content by 1.48 times, while it decreased by 41.32% under SWDS. The chemotype of EO was altered from t-anethole/estragole in WW seeds to t-anethole/β-bisabolene in treated seeds. Higher levels of total phenolics were detected in stressed seeds. Water deficit stress increased the amount of the major class, naringin, by 1.40 and 1.26 times under MWDS and SWDS. The evaluation of antioxidant activity through reducing power, DPPH, and chelating ability assays indicated that stressed seeds exhibited the highest activity. The study's findings suggest that the application of drought stress before harvesting can regulate the production of bioactive compounds, which can affect the industrial and nutritional values of anise seeds.

Stable isotopes in tree rings record physiological trends in Larix gmelinii after fires

Fire is an important regulator of ecosystem dynamics in boreal forests, and especially has a complicated association with growth and physiological processes of fire-tolerant tree species. Stable isotope ratios in tree rings are used extensively in eco-physiological studies for evaluating the impact of past environmental (e.g., drought, air pollution) factors on tree growth and physiological processes. Yet, such studies based on carbon (δ13C) and oxygen (δ18O) isotope ratios in tree rings are rarely conducted on fire effect, especially not well explored for fire-tolerant trees. In this study, we investigated variations in basal area increment and isotopes of Larix gmelinii (Rupr.) Rupr. before and after three moderate fires (different fire years) at three sites across the Great Xing'an Mountains, Northeastern China. We found that the radial growth of L. gmelinii trees has significantly declined after the fires across study sites. Following the fires, a simultaneous increase in δ13C and δ18O has strengthened the link between the two isotopes. Further, fires have significantly enhanced the 13C-derived intrinsic water-use efficiency (iWUE) and largely altered the relationships between δ13C, δ18O, iWUE and climate (temperature and precipitation). A dual-isotope conceptual model revealed that an initial co-increase in δ13C and δ18O in the fire year can be mainly attributed to a reduction in stomatal conductance with a constant photosynthetic rate. However, this physiological response would shift to different patterns over post-fire time between sites, which might be partly related to spring temperature. This study is beneficial to better understand, in a physiological perspective, how fire-tolerant tree species adapt to a fire-prone environment. We also remind that the limitation of model assumptions and constraints may challenge model applicability and further inferred physiological response.

Cold stress triggers freezing tolerance in wheat (Triticum aestivum L.) via hormone regulation and transcription of related genes

Low temperatures limit the geographic distribution and yield of plants. Hormones play an important role in coordinating the growth and development of plants and their tolerance to low temperatures. However, the mechanisms by which hormones affect plant resistance to extreme cold stress in the natural environment are still unclear. In this study, two winter wheat varieties with different cold resistances, Dn1 and J22, were used to conduct targeted plant hormone metabolome analysis on the tillering nodes of winter wheat at 5 °C, -10 °C and -25 °C using an LC-ESI-MS/MS system. We screened 39 hormones from 88 plant hormone metabolites and constructed a partial regulatory network of auxin, jasmonic acid and cytokinin. GO analysis and enrichment of KEGG pathways in different metabolites showed that the 'plant hormone signal transduction' pathway was the most common. Our study showed that extreme low temperature increased the most levels of auxin, cytokinin and salicylic acid, and decreased levels of jasmonic acid and abscisic acid, and that levels of auxin, jasmonic acid and cytokinin in Dn1 were higher than those in J22. These changes in hormone levels were associated with changes in gene expression in synthesis, catabolism, transport and signal transduction pathways. These results differ from the previous hormone regulation mechanisms, which were mostly obtained at 4 °C. Our results provide a basis for further understanding the molecular mechanisms by which plant endogenous hormones regulate plant freezing stress tolerance.

Selenium Regulates Antioxidant, Photosynthesis, and Cell Permeability in Plants under Various Abiotic Stresses: A Review

Plant growth is affected by various abiotic stresses, including water, temperature, light, salt, and heavy metals. Selenium (Se) is not an essential nutrient for plants but plays important roles in alleviating the abiotic stresses suffered by plants. This article summarizes the Se uptake and metabolic processes in plants and the functions of Se in response to water, temperature, light, salt, and heavy metal stresses in plants. Se promotes the uptake of beneficial substances, maintains the stability of plasma membranes, and enhances the activity of various antioxidant enzymes, thus alleviating adverse effects in plants under abiotic stresses. Future research directions on the relationship between Se and abiotic stresses in plants are proposed. This article will further deepen our understanding of the relationship between Se and plants.

Biochar as a soil amendment in the tree establishment phase: What are the consequences for tree physiology, soil quality and carbon sequestration?

Trees play a pivotal role in the urban environment alleviating the negative impacts of urbanization, and for this reason, local governments have promoted strongly tree planting policies. However, poor soil quality and neglect tree maintenance (e.g., irrigation and fertilization) can seriously mine the plant health status during the tree establishment phase. The use of biochar to provide long-lasting C to the soil and, at the same time, improving soil properties (e.g., improved water holding capacity), soil enzymes activities and NPK concentrations, is a promising research field. Therefore, with a two-step experiment, the study aimed to assay the physiological responses of a commonly used urban tree species (Tilia × europaea L.) to 1.5 % (w/w) biochar amendment (B), and secondly, to assess the ability of trees, grown in biochar amended soil, to tolerate a period of drought. Biochar amendment increased P and K availability in the soil, resulting in higher P and K concentrations in B than control leaves, according to the leaf stage. This induced B trees, higher values in both total biomass than controls (+22 %) in well-watered plants. Moreover, the higher water availability in soil amended with biochar helped B trees to tolerate water stress, with better leaf photosynthetic performances and a faster recovery than stressed controls after the re-watering. This study highlights the dual function of the biochar, improving CO₂ sequestration and soil properties, and at the same time, enhancing plant physiological responses to environmental constraints. The use of biochar at the tree planting, especially in an urban environment, is a feasible and environmentally sustainable strategy to improve the success during the tree establishment phase.

Regulatory mechanisms behind the phenotypic plasticity associated with Setaria italica water deficit tolerance

Drought is one of the main environmental stresses that negatively impacts vegetative and reproductive yield. Water deficit responses are determined by the duration and intensity of the stress, which, together with plant genotype, will define the chances of plant survival. The metabolic adjustments in response to water deficit are complex and involve gene expression modulation regulated by DNA-binding proteins and epigenetic modifications. This last mechanism may also regulate the activity of transposable elements, which in turn impact the expression of nearby loci. Setaria italica plants submitted to five water deficit regimes were analyzed through a phenotypical approach, including growth, physiological, RNA-seq and sRNA-seq analyses. The results showed a progressive reduction in yield as a function of water deficit intensity associated with signaling pathway modulation and metabolic adjustments. We identified a group of loci that were consistently associated with drought responses, some of which were related to water deficit perception, signaling and regulation. Finally, an analysis of the transcriptome and sRNAome allowed us to identify genes putatively regulated by TE- and sRNA-related mechanisms and an intriguing positive correlation between transcript levels and sRNA accumulation in gene body regions. These findings shed light on the processes that allow S. italica to overcome drought and survive under water restrictive conditions.

The role of potassium on drought resistance of winter wheat cultivars under cold dryland conditions: Probed by chlorophyll a fluorescence

Potassium (K) is an important cation that regulates plant metabolism. Therefore the effect of different concentrations of potassium (0, 75, 150 kg ha^-1 K₂SO₄) on photosynthesis efficiency of three winter wheat cultivars (Baran, Homa, Hashtrud) was investigated during the growing seasons of 2017-18 and 2018-19 under cold dryland conditions in Maragheh, Iran. Accumulation of potassium ion (K⁺) was observed to be increased with an increase in the concentration of K₂SO₄. With an increase in K⁺ the Hashtrud cultivar was observed to have more relative water content (RWC), normalized differential vegetation index (NDVI), and stomatal conductance (gs) than other cultivars. This resulted in a higher grain yield for the Hashtrud cultivar. RWC (R² = 0.97), NDVI (R² = 0.96), and gs (R² = 0.92) had a positive relationship with KUE (grain yield/unit of K fertilizer used), especially in dryer years. K deficiency induced hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) concentration in plants. The application of K increased superoxide dismutases and reduced abscisic acid, to maintain the plants' stomatal conductance. Chlorophyll a fluorescence (ChlF) and the calculation of double normalized relative variable fluorescence reveal detailed information's about the response of wheat plants to K application under dryland conditions. The application of a high concentration of K (150 kg ha^-1 K₂SO₄) on Hashtrud plants had a beneficial effect on the ChlF efficiency at different OJIP phases (KJ and JI). We found the efficiency of ChlF at the ΔW_K-I phase with the values of F_V/F_O and PI_ABS improved with the application of 150 kg ha^-1 K₂SO₄ and can be correlated with total yield improvement. These observations indicated that the application of a high concentration of K in stressed conditions for dryland areas could improve photosynthetic efficiency and wheat plant performance.

In situ pod growth rate reveals contrasting diurnal sensitivity to water deficit in Phaseolus vulgaris

The development of reproductive tissues determines plant fecundity and yield. Loading of resources into the developing reproductive tissue is thought to be under the co-limiting effects of source and sink strength. The dynamics of this co-limitation are unknown, largely due to an inability to measure the flux of resources into a developing sink. Here we use nuclear magnetic resonance (NMR) sensors to measure sink strength by quantifying rates of pod dry matter accumulation (pod loading) in Phaseolus vulgaris at 13-min intervals across the diel period. Rates of pod loading showed contrasting variation across light and dark periods during the onset of water deficit. In addition, rates of pod loading appeared decoupled from net photosynthetic rates when adjusted to the plant scale. Combined, these observations illustrate that the rate of pod development varies under water limitation and that continuous, non-invasive methodologies to measure sink strength provide insight into the governing processes that determine the development of reproductive tissues.

Drought adaptive microbes as bioinoculants for the horticultural crops

Drought stress is among the most destructive stresses for agricultural productivity. It interferes with normal metabolic activities of the plants resulting, a negative impact on physiology and morphology of the plants. The management of drought stress requires various adaptive and alleviation strategies in which stress adaptive microbiomes are exquisite bioresources for plant growth and alleviation of drought stress. Diverse drought adaptive microbes belonging to genera Achromobacter, Arthrobacter, Aspergillus, Bacillus, Pseudomonas, Penicillium and Streptomyces have been reported worldwide. These bioresources exhibit a wide range of mechanisms such as helping plant in nutrient acquisition, producing growth regulators, lowering the levels of stress ethylene, increasing the concentration of osmolytes, and preventing oxidative damage under water deficit environmental conditions. Horticulture is one of the potential agricultural sectors to speed up the economy, poverty and generation of employment for livelihood. The applications of drought adaptive plant growth promoting (PGP) microbes as biofertilizers and biopesticides for horticulture is a potential strategy to improve the productivity and protection of horticultural crops from abiotic and biotic stresses for agricultural sustainability.

Genetic Potential and Inheritance Patterns of Physiological, Agronomic and Quality Traits in Bread Wheat under Normal and Water Deficit Conditions

Water scarcity is a major environmental stress that adversatively impacts wheat growth, production, and quality. Furthermore, drought is predicted to be more frequent and severe as a result of climate change, particularly in arid regions. Hence, breeding for drought-tolerant and high-yielding wheat genotypes has become more decisive to sustain its production and ensure global food security with continuing population growth. The present study aimed at evaluating different parental bread wheat genotypes (exotic and local) and their hybrids under normal and drought stress conditions. Gene action controlling physiological, agronomic, and quality traits through half-diallel analysis was applied. The results showed that water-deficit stress substantially decreased chlorophyll content, photosynthetic efficiency (FV/Fm), relative water content, grain yield, and yield attributes. On the other hand, proline content, antioxidant enzyme activities (CAT, POD, and SOD), grain protein content, wet gluten content, and dry gluten content were significantly increased compared to well-watered conditions. The 36 evaluated genotypes were classified based on drought tolerance indices into 5 groups varying from highly drought-tolerant (group A) to highly drought-sensitive genotypes (group E). The parental genotypes P₃ and P₈ were identified as good combiners to increase chlorophyll b, total chlorophyll content, relative water content, grain yield, and yield components under water deficit conditions. Additionally, the cross combinations P₂ × P₄, P₃ × P₅, P₃ × P₈, and P₆ × P₇ were the most promising combinations to increase yield traits and multiple physiological parameters under water deficit conditions. Furthermore, P₁, P₂, and P₅ were recognized as promising parents to improve grain protein content and wet and dry gluten contents under drought stress. In addition, the crosses P₁ × P₄, P₂ × P₃, P₂ × P₅, P₂ × P₆, P₄ × P₇, P₅ × P₇, P₅ × P₈, P₆ × P₈, and P₇ × P₈ were the best combinations to improve grain protein content under water-stressed and non-stressed conditions. Certain physiological traits displayed highly positive associations with grain yield and its contributing traits under drought stress such as chlorophyll a, chlorophyll b, total chlorophyll content, photosynthetic efficiency (Fv/Fm), proline content, and relative water content, which suggest their importance for indirect selection under water deficit conditions. Otherwise, grain protein content was negatively correlated with grain yield, indicating that selection for higher grain yield could reduce grain protein content under drought stress conditions.

Influence of Ascophyllum nodosum Extract Foliar Spray on the Physiological and Biochemical Attributes of Okra under Drought Stress

Drought stress restricts the growth of okra (Abelmoschus esculentus L.) primarily by disrupting its physiological and biochemical functions. This study evaluated the role of Ascophyllum nodosum extract (ANE) in improving the drought tolerance of okra. Drought stress (3 days (control), 6 days (mild stress), and 9 days (severe stress)) and 4 doses of ANE (0, 0.1%, 0.2%, and 0.3%) were imposed after 30 days of cultivation. The results indicate that drought stress decreases the chlorophyll content (total chlorophyll, chlorophyll a, chlorophyll b, and carotenoid) but increases the activity of anthocyanin, proline, and antioxidant enzymes such as ascorbate peroxidase (APX), peroxidase (POD), and catalase (CAT). Physiological and biochemical plant disturbances and visible growth reduction in okra under drought stress were significantly decreased by the application of ANE foliar spray. ANE spray (0.3%) significantly increased the chlorophyll abundance and activity of anthocyanin, proline, and antioxidants (APX, POD, and CAT). ANE regulated and improved biochemical and physiological functions in okra under both drought and control conditions. The results of the current study show that ANE foliar spray may improve the growth performance of okra and result in the development of drought tolerance in okra.

Alleviation role of functional carbon nanodots for tomato growth and soil environment under drought stress

The biotoxicity and environmental applications of carbon nanomaterials have always been the focus of research. In this research, functional carbon nanodots (FCNs) show high promotion effects on regulating the growth, development and yield of tomato under drought stress, due to their up-regulation effects on the physiological processes of plants including photosynthesis, antioxidant system, osmotic adjustment, as well as soil amelioration in physicochemical properties and microbial environment during vegetative and reproductive growth stage. The reduction of tissue water content and water use efficiency are moderated by FCNs through improving root vigor and osmolytes (soluble sugar and proline) level, which contributes to maintain the enzyme function, photosynthesis and nutrient uptake in plant. FCNs regulate the enzymatic and non-enzymatic antioxidant system to scavenge reactive oxygen species (ROS) and inhibit the lipid peroxidation, thus protect the membrane structure and function of plant cells under stress. FCNs up-regulate soil microbial communities under drought stress by regulating the soil pH, enzyme activity, organic carbon and organic matters contents. Our results prove that FCNs are biological friendly to plant growth and soil environment under drought stress, thus exhibit potential as emendator to promote plant tolerance and improve agricultural productivity in water-deficient areas.

Biochar-Improved Growth and Physiology of Ehretia asperula under Water-Deficit Condition

Ehretia asperula’s physiological responses to growth performance following oak-wood biochar application under water stress conditions (WSC) and no water stress conditions (non-WSC) were investigated in a pot experiment. Biochar (WB) was incorporated into the soil at concentrations of 0, 5, 10, 15, and 20 tons ha−1 before transplanting Ehretia asperula in the pots. One month after transplanting, Ehretia asperula plants were put under water stress by withholding water for ten days. Water stress significantly decreased the growth and physiology of Ehretia asperula. Under WSC, the application of WB at the concentrations of 15 and 20 tons ha−1 to the soil increased the plant height; number of leaves; fresh and dry weight of the roots, shoots, and leaves; Fv/Fm; chlorophyll content; leaf relative water content; and soil moisture as well as decreased the relative ion leakage. The application of WB enhanced drought tolerance in Ehretia asperula plants by lowering the wilting point. The findings suggest that WB application at the concentration of 15 tons ha−1 could be recommended for ensuring the best physiological responses and highest growth of Ehretia asperula plants.

Sensitivities to temperature and evaporative demand in wheat relatives

There is potential sources of alleles and genes currently locked into wheat-related species that could be introduced into wheat breeding programs for current and future hot and dry climates. However, neither the intra- nor the inter-specific diversity of the responses of leaf growth and transpiration to temperature and evaporative demand have been investigated in a large diversity of wheat-related species. By analysing 12 groups of wheat-related sub-species, we questioned the n-dimensional structure of the genetic diversity for traits linked to plant vegetative structures and development, leaf expansion and transpiration together with their responses to "non-stressing" range of temperature and evaporative demand. In addition to provide new insight on how genome type, ploidy level, phylogeny and breeding pressure together structure this genetic diversity, this study provides new mathematical formalisms and the associated parameters of trait responses in the large genetic diversity of wheat-related species. This potentially allow crop models predicting the impact of this diversity on yield, and indicate potential sources of varietal improvement for modern wheat germplasms, through interspecific crosses.

In Vitro Nematocidal Effect and Anthelmintic Activity of Artemisia cina Against Haemonchus contortus in Gerbils and Relative Expression of Hc29 Gene in Transitional Larvae (L3-L4)

PURPOSE

(1) To assess the in vitro activity of Artemisia cina against Haemonchus contortus L₃ (HcL₃) and in transitional (L₃-L₄) larvae (HcTrL₃-L₄); (2) to quantify the relative expression of the Hc29 gene in HcTrL₃-L₄ exposed to the A. cina n-hexane extract; and (3) to assess the anthelmintic activity (AA) of the A. cina organic extracts in gerbils artificially infected with H. contortus (HcArt/inf/gerbs).

METHODS

The in vitro assay was carried out in 96-well microtitration plates. The following A. cina extracts: ethyl acetate (Ac-EtOAcEx), n-hexane (Ac-n-HexEx), and methanol (Ac-MethEx) were assessed at 1 and 2 mg/mL against HcL₃ and HcTrL₃-L₄ at 24 h exposure. Relative expression of the Hc29 gene in HcTrL₃-L₄ was obtained by RT-PCR. For assessing the AA, six groups of five HcArt/inf/gerbs were used. Groups were treated orally with 4 mg/kg BW of A. cina extracts. Five days after treatment, the gerbils were necropsied and nematodes counted.

RESULTS

The highest in vitro activities (75 and 82.6%) were shown by Ac-n-HexEx at 1 and 2 mg/mL, respectively. For HcTrL₃-L₄ the highest in vitro activities (69 and 23%) were shown by Ac-n-HexEx and isoguaiacine at 0.625 mg/mL, respectively. Also, upregulation of H. contortus Hc29 gene by 13- and 80-fold (p < 0.01) was observed on the HcTrL₃-L₄ stage after exposure to Ac-n-HexEx extract and isoguaiacine at 0.078 mg/mL, respectively. Reduction percentage was 100% in HcArt/inf/gerbs treated with Ac-n-HexEx.

CONCLUSIONS

We conclude that the Ac-n-HexEx and isoguaiacine compound had anthelmintic efficacy against H. contortus and L₃ and HcTrL₃-L₄.

Distinct cellular strategies determine sensitivity to mild drought of Arabidopsis natural accessions

The worldwide distribution of Arabidopsis (Arabidopsis thaliana) accessions imposes different types of evolutionary pressures, which contributes to various responses of these accessions to environmental stresses. Responses to drought stress have mostly been studied in the Columbia accession, which is predominantly used in plant research. However, the reactions to drought stress are complex and our understanding of the responses that contribute to maintaining plant growth during mild drought (MD) is very limited. Here, we studied the mechanisms with which natural accessions react to MD at a physiological and molecular level during early leaf development. We documented variations in MD responses among natural accessions and used transcriptome sequencing of a drought-sensitive accession, ICE163, and a drought-insensitive accession, Yeg-1, to gain insights into the mechanisms underlying this discrepancy. This revealed that ICE163 preferentially induces jasmonate- and anthocyanin-related pathways, which are beneficial in biotic stress defense, whereas Yeg-1 has a more pronounced activation of abscisic acid signaling, the classical abiotic stress response. Related physiological traits, including the content of proline, anthocyanins, and reactive oxygen species, stomatal closure, and cellular leaf parameters, were investigated and linked to the transcriptional responses. We can conclude that most of these processes constitute general drought response mechanisms that are regulated similarly in drought-insensitive and -sensitive accessions. However, the capacity to close stomata and maintain cell expansion under MD appeared to be major factors that allow to better sustain leaf growth under MD.

Exogenous salicylic acid alleviates the negative impacts on production components, biomass and gas exchange in tomato plants under water deficit improving redox status and anatomical responses

Salicylic acid (SA) is an interesting messenger in plant metabolism that modulates multiple pathways, including the antioxidant defence pathway, and stimulates anatomical structures essential to carbon dioxide fixation during the photosynthetic process. The aim of this research was to determine whether pre-treatment with exogenous SA can alleviate the deleterious effects induced by water deficit on production components, biomass and gas exchange, measuring reactive oxygen species, antioxidant enzymes, variables connected to photosynthetic machinery, anatomical responses, and agro-morphological traits in tomato plants under water deficit. The experiment used a factorial design with four treatments, including two water conditions (control and water deficit) and two salicylic acid concentrations (0 and 0.1 mM salicylic acid). Water deficit negatively impacted the biomass and fruit number of tomato plants. Pre-treatment using 0.1 mM SA in plants submitted to water restriction induced increments in fruit number, weight, and biomass. These results were related to the protective role triggered by this substance, stimulating superoxide dismutase (27.07%), catalase (17.81%), ascorbate peroxidase (50.52%), and peroxidase (10.81%) as well as reducing the cell damage (malondialdehyde and electrolyte leakage) caused by superoxide and hydrogen peroxide. Simultaneously, application of SA improved the net photosynthetic rate (84.55%) and water-use efficiency (65.00%) of stressed plants in which these factors are connected to anatomical benefits, as verified by stomatal density, palisade and spongy parenchyma, combined with improved performance linked to photosystem II.

Minimizing hazard impacts of soil salinity and water stress on wheat plants by soil application of vermicompost and biochar

Soil water and nutrient status are two of the most important factors for plant development and crop yield. Vermicompost and biochar are supposed to amend soil attributes and increase the productivity. However, little is known about their mixture application on soil quality and nutrient uptake under natural conditions. The aim of this investigation was to understand the impact of soil amendments (control, vermicompost, biochar, and vermicompost + biochar) on yield, soil quality, physiological and biochemical attributes, as well as nutrient uptake of wheat plants grown at different irrigation water treatments (50%, 75%, and 100% of field capacity [FC]) in saline sodic soil. Vermicompost improved wheat growth and yield. Biochar-treated plants had higher growth performance and yield than control plants in all traits and than vermicompost in some cases, thus confirming its potential for enhancing soil quality and increasing nutrient uptake, which stimulates soil chemical properties. When vermicompost was added in combination with biochar, further enhancement in the growth and yield was recorded, highlighting the beneficial effect of vermicompost on plant yield. Vermicompost-biochar mixture application followed by biochar as a singular application caused significant improvements in relative water content, chlorophyll content, stomatal conductance, cytotoxicity, leaf K⁺ content with respect to nutrient uptake (N, P, and K), while reducing oxidative stress (i.e., activities of catalase [CAT] and ascorbate peroxidase [APX], and expression levels of CAT, APX, and Mn-SOD genes), leaf Na⁺ content, and proline content. This resulted in increases in yield-related traits and productivity owing to the enhancement in soil chemical characteristics and soil moisture content. Grain yield and nutrient uptake attained the highest values at 75% FC in wheat plants treated by the combination of vermicompost and biochar. In summary, this investigation revealed that the synergistic effect of vermicompost and biochar can not only enhance crop production but also eliminates the detrimental effects of soil salinity and water stress.

Biochar as a tool for effective management of drought and heavy metal toxicity

Drought and heavy metal stress undesirably disturb soil fertility and plant growth. Heavy metals pose severe biological toxic effects. Biochar, a carbon rich source application ameliorates this stress by increasing the plant growth, biomass, nutrient uptake and improves gaseous exchange in drought stress. Application of biochar reduces drought stress by increasing water holding capacity of soil through modification of soil physio-chemical properties that in turn increases water availability to plants and also enhances mineral uptake and regulation of stomatal conductance. Biochar mediates the retention of moisture, nutrients, inhibits harmful bacteria, absorbs heavy metals, pesticides, prevents soil erosion, increases soil pH, improves cationic exchange and boosts soil fertility. Drought and heavy metal stress often lead to production of reactive oxygen species. However, biochar significantly modifies the Reactive Oxygen Species (ROS) scavenging enzymes and provides an efficient electron transferring mechanism to tackle the toxic effects of ROS in plants. Biochar is regarded as a tool for the effective management of agricultural productivity and various environmental issues. This review provides insights on the potential role of biochar in ameliorating drought and heavy metal stress.

Turgor-time controls grass leaf elongation rate and duration under drought stress

The process of leaf elongation in grasses is characterized by the creation and transformation of distinct cell zones. The prevailing turgor pressure within these cells is one of the key drivers for the rate at which these cells divide, expand and differentiate, processes that are heavily impacted by drought stress. In this article, a turgor-driven growth model for grass leaf elongation is presented, which combines mechanistic growth from the basis of turgor pressure with the ontogeny of the leaf. Drought-induced reductions in leaf turgor pressure result in a simultaneous inhibition of both cell expansion and differentiation, lowering elongation rate but increasing elongation duration due to the slower transitioning of cells from the dividing and elongating zone to mature cells. Leaf elongation is, therefore, governed by the magnitude of, and time spent under, growth-enabling turgor pressure, a metric which we introduce as turgor-time. Turgor-time is able to normalize growth patterns in terms of varying water availability, similar to how thermal time is used to do so under varying temperatures. Moreover, additional inclusion of temperature dependencies within our model pioneers a novel concept enabling the general expression of growth regardless of water availability or temperature.

Dynamics of cell wall structure and related genomic resources for drought tolerance in rice

Cell wall plasticity plays a very crucial role in vegetative and reproductive development of rice under drought and is a highly potential trait for improving rice yield under drought. Drought is a major constraint in rice (Oryza sativa L.) cultivation severely affecting all developmental stages, with the reproductive stage being the most sensitive. Rice plants employ multiple strategies to cope with drought, in which modification in cell wall dynamics plays a crucial role. Over the years, significant progress has been made in discovering the cell wall-specific genomic resources related to drought tolerance at vegetative and reproductive stages of rice. However, questions remain about how the drought-induced changes in cell wall made by these genomic resources potentially influence the vegetative and reproductive development of rice. The possibly major candidate genes underlying the function of quantitative trait loci directly or indirectly associated with the cell wall plasticization-mediated drought tolerance of rice might have a huge promise in dissecting the putative genomic regions associated with cell wall plasticity under drought. Furthermore, engineering the drought tolerance of rice using cell wall-related genes from resurrection plants may have huge prospects for rice yield improvement. Here, we review the comprehensive multidisciplinary analyses to unravel different components and mechanisms involved in drought-induced cell wall plasticity at vegetative and reproductive stages that could be targeted for improving rice yield under drought.

Combating Dual Challenges in Maize Under High Planting Density: Stem Lodging and Kernel Abortion

High plant density is considered a proficient approach to increase maize production in countries with limited agricultural land; however, this creates a high risk of stem lodging and kernel abortion by reducing the ratio of biomass to the development of the stem and ear. Stem lodging and kernel abortion are major constraints in maize yield production for high plant density cropping; therefore, it is very important to overcome stem lodging and kernel abortion in maize. In this review, we discuss various morphophysiological and genetic characteristics of maize that may reduce the risk of stem lodging and kernel abortion, with a focus on carbohydrate metabolism and partitioning in maize. These characteristics illustrate a strong relationship between stem lodging resistance and kernel abortion. Previous studies have focused on targeting lignin and cellulose accumulation to improve lodging resistance. Nonetheless, a critical analysis of the literature showed that considering sugar metabolism and examining its effects on lodging resistance and kernel abortion in maize may provide considerable results to improve maize productivity. A constructive summary of management approaches that could be used to efficiently control the effects of stem lodging and kernel abortion is also included. The preferred management choice is based on the genotype of maize; nevertheless, various genetic and physiological approaches can control stem lodging and kernel abortion. However, plant growth regulators and nutrient application can also help reduce the risk for stem lodging and kernel abortion in maize.

Suppressed ABA signal transduction in the spike promotes sucrose use in the stem and reduces grain number in wheat under water stress

Water stress is a primary trigger for reducing grain number per spike in wheat during the reproductive period. However, under stress conditions, the responses of plant organs and the interactions between them at the molecular and physiological levels remain unclear. In this study, when water stress occurred at the young microspore stage, RNA-seq data indicated that the spike had 970 differentially expressed genes, while the stem, comprising the two internodes below the spike (TIS), had 382. Abscisic acid (ABA) signal transduction genes were down-regulated by water stress in both these tissues, although to a greater extent in the TIS than in the spike. A reduction in sucrose was observed, and was accompanied by increases in cell wall invertase (CWIN) and sucrose:sucrose 1-fructosyl-transferase (1-SST) activities. Hexose and fructan were increased in the TIS but decreased in the spike. ABA was increased in the spike and TIS, and showed significant positive correlation with CWIN and 1-SST activities in the TIS. Overall, our results suggest that water stress induces the conversion of sucrose to hexose by CWIN, and to fructan by 1-SST, due to increased down-regulation of ABA signal transduction related-genes in the TIS; this leads to deficient sucrose supply to the spike and a decrease in grain number.

The AP2 transcription factor NtERF172 confers drought resistance by modifying NtCAT

Drought stress often limits plant growth and global crop yields. Catalase (CAT)-mediated hydrogen peroxide (H2 O2 ) scavenging plays an important role in the adaptation of plant stress responses, but the transcriptional regulation of the CAT gene in response to drought stress is not well understood. Here, we isolated an APETALA2/ETHYLENE-RESPONSIVE FACTOR (AP2/ERF) domain-containing transcription factor (TF), NtERF172, which was strongly induced by drought, abscisic acid (ABA) and H2 O2 , from tobacco (Nicotiana tabacum) by yeast one-hybrid screening. NtERF172 localized to the nucleus and acted as a transcriptional activator. Chromatin immunoprecipitation, yeast one-hybrid assays, electrophoretic mobility shift assays and transient expression analysis assays showed that NtERF172 directly bound to the promoter region of the NtCAT gene and positively regulated its expression. Transgenic plants overexpressing NtERF172 displayed enhanced tolerance to drought stress, whereas suppression of NtERF172 decreased drought tolerance. Under drought stress conditions, the NtERF172-overexpressed lines showed higher catalase activity and lower accumulation of H2 O2 compared with wild-type (WT) plants, while the NtERF172-silenced plants showed the inverse correlation. Exogenous application of amino-1,2,4-triazole (3-AT), an irreversible CAT inhibitor, to the NtERF172-overexpression lines showed decreased catalase activity and drought tolerance, and increased levels of cellular H2 O2 . Knockdown of NtCAT in the NtERF172-overexpression lines displayed a more drought stress-sensitive phenotype than NtERF172-overexpression lines. We propose that NtERF172 acts as a positive factor in drought stress tolerance, at least in part through the regulation of CAT-mediated H2 O2 homeostasis.

Disentangling the effects of atmospheric CO2 and climate on intrinsic water-use efficiency in South Asian tropical moist forest trees

Due to the increase in atmospheric CO2 concentrations, the ratio of carbon fixed by assimilation to water lost by transpiration through stomatal conductance (intrinsic water-use efficiency, iWUE) shows a long-term increasing trend globally. However, the drivers of short-term (inter-annual) variability in iWUE of tropical trees are poorly understood. We studied the inter-annual variability in iWUE of three South Asian tropical moist forest tree species (Chukrasia tabularis A.Juss., Toona ciliata M. Roem. and Lagerstroemia speciosa L.) derived from tree-ring stable carbon isotope ratio (δ13C) in response to variations of environmental conditions. We found a significantly decreasing trend in carbon discrimination (Δ13C) and an increasing trend in iWUE in all the three species, with a species-specific long-term trend in intercellular CO2 concentration (Ci). Growing season temperatures were the main driver of inter-annual variability of iWUE in C. tabularis and L. speciosa, whereas previous year temperatures determined the iWUE variability in T. ciliata. Vapor pressure deficit was linked with iWUE only in C. tabularis. Differences in shade tolerance, tree stature and canopy position might have caused this species-specific variation in iWUE response to climate. Linear mixed effect modeling successfully simulated iWUE variability, explaining 41-51% of the total variance varying with species. Commonality analysis revealed that temperatures had a dominant influence on the inter-annual iWUE variability (64-77%) over precipitation (7-22%) and atmospheric CO2 concentration (3-6%). However, the long-term variations in iWUE were explicitly determined by the atmospheric CO2 increase (83-94%). Our results suggest that the elevated CO2 and concomitant global warming might have detrimental effects on gas exchange and other physiological processes in South Asian tropical moist forest trees.

Maize, sorghum, and pearl millet have highly contrasting species strategies to adapt to water stress and climate change-like conditions

This study compared maize, sorghum and pearl-millet, leading C₄ cereals, for the transpiration rate (TR) response to increasing atmospheric and soil water stress. The TR response to transiently increasing VPD (0.9-4.1 kPa) and the transpiration and leaf area expansion response to progressive soil drying were measured in controlled conditions at early vegetative stage in 10-16 genotypes of each species grown in moderate or high vapor pressure deficit (VPD) conditions. Maize grown under moderate VPD conditions restricted TR under high VPD, but not sorghum and pearl millet. By contrast, when grown under high VPD, all species increased TR upon increasing VPD, suggesting a loss of TR responsiveness. Sorghum and pearl-millet grown under high VPD reduced leaf area, but not maize. Upon progressive soil drying, maize reduced transpiration at higher soil moisture than sorghum and pearl millet, especially under high VPD, and leaf area expansion declined at similar or lower soil moisture than transpiration in maize and sorghum. It is concluded that maize conserves water by restricting transpiration upon increasing VPD and under higher soil moisture than sorghum and millet, giving maize significantly higher TE, whereas sorghum and pearl millet rely mostly on reduced leaf area and somewhat on transpiration restriction.

Over-accumulation of abscisic acid in transgenic tomato plants increases the risk of hydraulic failure

Climate change threatens food security, and plant science researchers have investigated methods of sustaining crop yield under drought. One approach has been to overproduce abscisic acid (ABA) to enhance water use efficiency. However, the concomitant effects of ABA overproduction on plant vascular system functioning are critical as it influences vulnerability to xylem hydraulic failure. We investigated these effects by comparing physiological and hydraulic responses to water deficit between a tomato (Solanum lycopersicum) wild type control (WT) and a transgenic line overproducing ABA (sp12). Under well-watered conditions, the sp12 line displayed similar growth rate and greater water use efficiency by operating at lower maximum stomatal conductance. X-ray microtomography revealed that sp12 was significantly more vulnerable to xylem embolism, resulting in a reduced hydraulic safety margin. We also observed a significant ontogenic effect on vulnerability to xylem embolism for both WT and sp12. This study demonstrates that the greater water use efficiency in the tomato ABA overproducing line is associated with higher vulnerability of the vascular system to embolism and a higher risk of hydraulic failure. Integrating hydraulic traits into breeding programmes represents a critical step for effectively managing a crop's ability to maintain hydraulic conductivity and productivity under water deficit.

X-ray fluorescence spectroscopy (XRF) applied to plant science: challenges towards in vivo analysis of plants

X-ray fluorescence spectroscopy (XRF) is an analytical tool used to determine the elemental composition in a myriad of sample matrices. Due to the XRF non-destructive feature, this technique may allow time-resolved plant tissue analyses under in vivo conditions, and additionally, the combination with other non-destructive techniques. In this study, we employed handheld and benchtop XRF to evaluate the elemental distribution changes in living plant tissues exposed to X-rays, as well as real-time uptake kinetics of Zn(aq) and Mn(aq) in soybean (Glycine max (L.) Merrill) stem and leaves, for 48 hours, combined with transpiration rate assessment on leaves by an infrared gas analyzer (IRGA). We found higher Zn content than Mn in stems. The latter micronutrient, in turn, presented higher concentration in leaf veins. Besides, both micronutrients were more concentrated in the first trifolium (i.e., youngest leaf) of soybean plants. Moreover, the transpiration rate was more influenced by circadian cycles than Zn and Mn uptake. Thus, XRF represents a convenient tool for in vivo nutritional studies in plants, and it can be coupled successfully to other analytical techniques.

The Dynamic Responses of Cell Walls in Resurrection Plants During Dehydration and Rehydration

Plant cell walls define the shape of the cells and provide mechanical support. They function as osmoregulators by controlling the transport of molecules between cells and provide transport pathways within the plant. These diverse functions require a well-defined and flexible organization of cell wall components, i.e., water, polysaccharides, proteins, and other diverse substances. Cell walls of desiccation tolerant resurrection plants withstand extreme mechanical stress during complete dehydration and rehydration. Adaptation to the changing water status of the plant plays a crucial role during this process. This review summarizes the compositional and structural variations, signal transduction and changes of gene expression which occur in cell walls of resurrection plants during dehydration and rehydration.

Abscisic acid signalling mediates biomass trade-off and allocation in poplar

Abscisic acid (ABA) is a well known stress hormone regulating drought adaptation of plants. Here, we hypothesised that genetic engineering of genes involved in ABA stress signalling and photoperiodic regulation affected drought resistance by trade-off with biomass production in perennial poplar trees. We grew Populus tremula × tremuloides wild-type (T89) and various transgenic lines (two transformation events of 35S::abi1-1, 35S::RCAR, RCAR:RNAi, 35S::ABI3, 35S::AREB3, 35S::FDL1, FDL1:RNAi, 35S::FDL2 and FDL2:RNAi) outdoors and exposed them to drought in the second growth period. After the winter, the surviving lines showed a huge variation in stomatal conductance, leaf size, whole-plant leaf area, tree height, stem diameter, and biomass. Whole-plant leaf area was a strong predictor for woody biomass production. The 35S::AREB3 lines were compromised in biomass production under well irrigated conditions compared with wild-type poplars but were resilient to drought. ABA signalling regulated FDL1 and FDL2 expression under stress. Poplar lines overexpressing FDL1 or FDL2 were drought-sensitive; they shed leaves and lost root biomass, whereas the FDL RNAi lines showed higher biomass allocation to roots under drought. These results assign a new function in drought acclimation to FDL genes aside from photoperiodic regulation. Our results imply a critical role for ABA-mediated processes in balancing biomass production and climate adaptation.

Transcript and metabolic adjustments triggered by drought in Ilex paraguariensis leaves

Abscisic acid is involved in the drought response of Ilex paraguariensis. Acclimation includes root growth stimulation, stomatal closure, osmotic adjustment, photoprotection, and regulation of nonstructural carbohydrates and amino acid metabolisms. Ilex paraguariensis (yerba mate) is cultivated in the subtropical region of South America, where the occurrence of drought episodes limit yield. To explore the mechanisms that allow I. paraguariensis to overcome dehydration, we investigated (1) how gene expression varied between water-stressed and non-stressed plants and (2) in what way the modulation of gene expression was linked to physiological status and metabolite composition. A total of 4920 differentially expressed transcripts were obtained through RNA-Seq after water deprivation. Drought induced the expression of several transcripts involved in the ABA-signalling pathway. Stomatal closure and leaf osmotic adjustments were promoted to minimize water loss, and these responses were accompanied by a high transcriptional remodeling of stress perception, signalling and transcriptional regulation, the photoprotective and antioxidant systems, and other stress-responsive genes. Simultaneously, significant changes in metabolite contents were detected. Glutamine, phenylalanine, isomaltose, fucose, and malate levels were shown to be positively correlated with dehydration. Principal component analysis showed differences in the metabolic profiles of control and stressed leaves. These results provide a comprehensive overview of how I. paraguariensis responds to dehydration at transcriptional and metabolomic levels and provide further characterization of the molecular mechanisms associated with drought response in perennial subtropical species.

Recent advances in the characterization of plant transcriptomes in response to drought, salinity, heat, and cold stress

Despite recent advancements in plant molecular biology and biotechnology, providing food security for an increasing world population remains a challenge. Drought (water scarcity), salinity, heat, and cold stress are considered major limiting factors that affect crop production both qualitatively and quantitatively. Therefore, the development of cost-effective and environmentally friendly strategies will be needed to resolve these agricultural problems. This will require a comprehensive understanding of transcriptomic alterations that occur in plants in response to varying levels of environmental stresses, singly and in combination. Here, we briefly discuss the current status and future challenges in plant research related to understanding transcriptional changes that occur in response to drought, salinity, heat, and cold stress.

Genetic and environmental dissection of biomass accumulation in multi-genotype maize canopies

Multi-genotype canopies are frequent in phenotyping experiments and are of increasing interest in agriculture. Radiation interception efficiency (RIE) and radiation use efficiency (RUE) have low heritabilities in such canopies. We propose a revised Monteith equation that identifies environmental and genetic components of RIE and RUE. An environmental term, a component of RIE, characterizes the effect of the presence or absence of neighbours on light interception. The ability of a given plant to compete with its neighbours is then identified, which accounts for the genetic variability of RIE of plants having similar leaf areas. This method was used in three experiments in a phenotyping platform with 765 plants of 255 maize hybrids. As expected, the heritability of the environmental term was near zero, whereas that of the competitiveness term increased with phenological stage, resulting in the identification of quantitative trait loci. In the same way, RUE was dissected as an effect of intercepted light and a genetic term. This approach was used for predicting the behaviour of individual genotypes in virtual multi-genotype canopies. A large effect of competitiveness was observed in multi-genotype but not in single-genotype canopies, resulting in a bias for genotype comparisons in breeding fields.

Heliaphen, an Outdoor High-Throughput Phenotyping Platform for Genetic Studies and Crop Modeling

Heliaphen is an outdoor platform designed for high-throughput phenotyping. It allows the automated management of drought scenarios and monitoring of plants throughout their lifecycles. A robot moving between plants growing in 15-L pots monitors the plant water status and phenotypes the leaf or whole-plant morphology. From these measurements, we can compute more complex traits, such as leaf expansion (LE) or transpiration rate (TR) in response to water deficit. Here, we illustrate the capabilities of the platform with two practical cases in sunflower (Helianthus annuus): a genetic and genomic study of the response of yield-related traits to drought, and a modeling study using measured parameters as inputs for a crop simulation. For the genetic study, classical measurements of thousand-kernel weight (TKW) were performed on a biparental population under automatically managed drought stress and control conditions. These data were used for an association study, which identified five genetic markers of the TKW drought response. A complementary transcriptomic analysis identified candidate genes associated with these markers that were differentially expressed in the parental backgrounds in drought conditions. For the simulation study, we used a crop simulation model to predict the impact on crop yield of two traits measured on the platform (LE and TR) for a large number of environments. We conducted simulations in 42 contrasting locations across Europe using 21 years of climate data. We defined the pattern of abiotic stresses occurring at the continental scale and identified ideotypes (i.e., genotypes with specific trait values) that are more adapted to specific environment types. This study exemplifies how phenotyping platforms can assist the identification of the genetic architecture controlling complex response traits and facilitate the estimation of ecophysiological model parameters to define ideotypes adapted to different environmental conditions.

Comprehensive Analysis of Differentially Expressed Unigenes under NaCl Stress in Flax (Linum usitatissimum L.) Using RNA-Seq

Flax (Linum usitatissimum L.) is an important industrial crop that is often cultivated on marginal lands, where salt stress negatively affects yield and quality. High-throughput RNA sequencing (RNA-seq) using the powerful Illumina platform was employed for transcript analysis and gene discovery to reveal flax response mechanisms to salt stress. After cDNA libraries were constructed from flax exposed to water (negative control) or salt (100 mM NaCl) for 12 h, 24 h or 48 h, transcription expression profiles and cDNA sequences representing expressed mRNA were obtained. A total of 431,808,502 clean reads were assembled to form 75,961 unigenes. After ruling out short-length and low-quality sequences, 33,774 differentially expressed unigenes (DEUs) were identified between salt-stressed and unstressed control (C) flax. Of these DEUs, 3669, 8882 and 21,223 unigenes were obtained from flax exposed to salt for 12 h (N1), 24 h (N2) and 48 h (N4), respectively. Gene function classification and pathway assignments of 2842 DEUs were obtained by comparing unigene sequences to information within public data repositories. qRT-PCR of selected DEUs was used to validate flax cDNA libraries generated for various durations of salt exposure. Based on transcriptome sequences, 1777 EST-SSRs were identified of which trinucleotide and dinucleotide repeat microsatellite motifs were most abundant. The flax DEUs and EST-SSRs identified here will serve as a powerful resource to better understand flax response mechanisms to salt exposure for development of more salt-tolerant varieties of flax.

The Plant-Transpiration Response to Vapor Pressure Deficit (VPD) in Durum Wheat Is Associated With Differential Yield Performance and Specific Expression of Genes Involved in Primary Metabolism and Water Transport

The regulation of plant transpiration was proposed as a key factor affecting transpiration efficiency and agronomical adaptation of wheat to water-limited Mediterranean environments. However, to date no studies have related this trait to crop performance in the field. In this study, the transpiration response to increasing vapor pressure deficit (VPD) of modern Spanish semi-dwarf durum wheat lines was evaluated under controlled conditions at vegetative stage, and the agronomical performance of the same set of lines was assessed at grain filling as well as grain yield at maturity, in Mediterranean environments ranging from water stressed to good agronomical conditions. A group of linear-transpiration response (LTR) lines exhibited better performance in grain yield and biomass compared to segmented-transpiration response (STR) lines, particularly in the wetter environments, whereas the reverse occurred only in the most stressed trial. LTR lines generally exhibited better water status (stomatal conductance) and larger green biomass (vegetation indices) during the reproductive stage than STR lines. In both groups, the responses to growing conditions were associated with the expression levels of dehydration-responsive transcription factors (DREB) leading to different performances of primary metabolism-related enzymes. Thus, the response of LTR lines under fair to good conditions was associated with higher transcription levels of genes involved in nitrogen (GS1 and GOGAT) and carbon (RCBL) metabolism, as well as water transport (TIP1.1). In conclusion, modern durum wheat lines differed in their response to water loss, the linear transpiration seemed to favor uptake and transport of water and nutrients, and photosynthetic metabolism led to higher grain yield except for very harsh drought conditions. The transpiration response to VPD may be a trait to further explore when selecting adaptation to specific water conditions.

Selenium protects rice plants from water deficit stress

Selenium (Se) is essential to humans and animals due to its antioxidant properties. Although it is not considered an essential nutrient for higher plants. Many studies show that Se in low concentrations (up to 0.5 mg kg^-1) provides beneficial effects to non-hyperaccumulating plants by participating in antioxidant defense systems and enhancing tolerance to abiotic stress. Therefore, this study aimed to evaluate the effects of Se application rates on rice plants under different soil water conditions. The experiment was conducted on an Oxisol using four Se rates (0, 0.5, 1.0 and 2.0 mg kg^-1) and two soil water conditions (irrigated and water deficit). Selenium application via soil up to 0.5 mg kg^-1 increased the plant height, chlorophyll index, sulfur and copper accumulation in shoots, carbon dioxide assimilation, superoxide dismutase (EC 1.15.1.1) activity and decreased the hydrogen peroxide concentration in rice leaves. The accumulation of Se in shoot biomass and Se concentration in seeds increased linearly with the applied rates. Water deficit strongly decreased the plant growth and yield. However, rice plants treated with Se showed higher net photosynthesis, water use efficiency and antioxidant system. This study provides useful information about the roles of Se in protecting rice plants from water deficit stress.