Water Stress Response Research Articles

Drivers of habitat partitioning among three Quercus species along a hydrologic gradient.

A critical process that allows multiple, similar species to coexist in an ecological community is their ability to partition local habitat gradients. The mechanisms that underlie this separation at local scales may include niche differences associated with their biogeographic history, differences in ecological function associated with the degree of shared ancestry and trait-based performance differences, which may be related to spatial or temporal variation in habitat. In this study we measured traits related to water-use, growth and stress tolerance in mature trees and seedlings of three oak species (Quercus alba L., Quercus falcata Michx. and Quercus palustris Münchh). which co-occur in temperate forests across the eastern USA but tend to be found in contrasting hydrologic environments. The three species showed significant differences in their local distributions along a hydrologic gradient. We tested three possible mechanisms that influence their contrasting local environmental distributions and promote their long-term co-existence: (i) differences in their climatic distributions across a broad geographic range, (ii) differences in functional traits related to water use, drought tolerance and growth and (iii) contrasting responses to temporal variation in water availability. We identified key differences between the species in both their range-wide climatic distributions (especially aridity index and mean annual temperature) and physiological traits in mature trees and seedlings, including daily water loss, hydraulic conductance, stress responses, growth rate and biomass allocation. Taken together, these differences explain the habitat partitioning that allows three closely related species to co-occur locally.

Modeling Hyperspectral Response of Water-Stress Induced Lettuce Plants Using Artificial Neural Networks

Modeling the hyperspectral response of vegetables is important for estimating water stress through a noninvasive approach. This article evaluates the hyperspectral response of water-stress induced lettuce (Lactuca sativa L.) using artificial neural networks (ANN). We evenly split 36 lettuce pots into three groups: control, stress, and bacteria. Hyperspectral response was measured four times, during 14 days of stress induction, with an ASD Fieldspec HandHeld spectroradiometer (325–1075 nm). Both reflectance and absorbance measurements were calculated. Different biophysical parameters were also evaluated. The performance of the ANN approach was compared against other machine learning algorithms. Our results show that the ANN approach could separate the water-stressed lettuce from the non-stressed group with up to 80% accuracy at the beginning of the experiment. Additionally, this accuracy improved at the end of the experiment, reaching an accuracy of up to 93%. Absorbance data offered better accuracy than reflectance data to model it. This study demonstrated that it is possible to detect early stages of water stress in lettuce plants with high accuracy based on an ANN approach applied to hyperspectral data. The methodology has the potential to be applied to other species and cultivars in agricultural fields.

Evaluating Remotely-Sensed Grapevine (Vitis vinifera L.) Water Stress Responses Across a Viticultural Region

The evolving spatial and temporal knowledge about vineyard performance through the use of remote sensing offers new perspectives for vine water status studies. This paper describes the application of aerial thermal imaging to evaluate vine water status to improve irrigation scheduling decisions, water use efficiency, and overall winegrape quality in the Coonawarra viticultural region of South Australia. Airborne infrared images were acquired during the 2016 and 2017 growing seasons in the region of Coonawarra, South Australia. Several thermal indices of crop water status (CWSI, Ig, (Tc-Ta)) were calculated that correlated with conventional soil and vine water status measures (Ψpd, Ψs, gs). CWSI and Ig could discriminate between the two cultivars used in this study, Cabernet Sauvignon (CAS) and Shiraz (SHI), as did the conventional water stress measures. The relationship between conventional vine water status measures appeared stronger with CWSI in the warmer and drier season (2016) compared to the cooler and wetter season (2017), where Ig and (Tc-Ta) showed stronger correlations. The study identified CWSI, Ig and (Tc-Ta) to be reliable indicators of vine water status under a variety of environmental conditions. This is the first study to report on high resolution vine water status at a regional scale in Australia using a combination of remote and direct sensing methods. This methodology is promising for aerial surveillance of vine water status across multiple blocks and cultivars to inform irrigation scheduling.

A Novel Image-Based Screening Method to Study Water-Deficit Response and Recovery of Barley Populations Using Canopy Dynamics Phenotyping and Simple Metabolite Profiling.

Plant phenotyping platforms offer automated, fast scoring of traits that simplify the selection of varieties that are more competitive under stress conditions. However, indoor phenotyping methods are frequently based on the analysis of plant growth in individual pots. We present a reproducible indoor phenotyping method for screening young barley populations under water stress conditions and after subsequent rewatering. The method is based on a simple read-out of data using RGB imaging, projected canopy height, as a useful feature for indirectly following the kinetics of growth and water loss in a population of barley. A total of 47 variables including 15 traits and 32 biochemical metabolites measured (morphometric parameters, chlorophyll fluorescence imaging, quantification of stress-related metabolites; amino acids and polyamines, and enzymatic activities) were used to validate the method. The study allowed the identification of metabolites related to water stress response and recovery. Specifically, we found that cadaverine (Cad), 1,3-aminopropane (DAP), tryptamine (Tryp), and tyramine (Tyra) were the major contributors to the water stress response, whereas Cad, DAP, and Tyra, but not Tryp, remained at higher levels in the stressed plants even after rewatering. In this work, we designed, optimized and validated a non-invasive image-based method for automated screening of potential water stress tolerance genotypes in barley populations. We demonstrated the applicability of the method using transgenic barley lines with different sensitivity to drought stress showing that combining canopy height and the metabolite profile we can discriminate tolerant from sensitive genotypes. We showed that the projected canopy height a sensitive trait that truly reflects other invasively studied morphological, physiological, and metabolic traits and that our presented methodological setup can be easily applicable for large-scale screenings in low-cost systems equipped with a simple RGB camera. We believe that our approach will contribute to accelerate the study and understanding of the plant water stress response and recovery capacity in crops, such as barley.

Maize yield under a changing climate: The hidden role of vapor pressure deficit

Temperatures over the next century are expected to rise to levels detrimental to crop growth and yield. As the atmosphere warms without additional water vapor input, vapor pressure deficit (VPD) increases as well. Increased temperatures and accompanied elevated VPD levels can both lead to negative impacts on crop yield. The independent importance of VPD, however, is often neglected or conflated with that from temperature due to a tight correlation between the two climate factors. We used a coupled process-based crop (MAIZSIM) and soil (2DSOIL) model to gain a mechanistic understanding of the independent roles temperature and VPD play in crop yield projections, as well as their interactions with rising CO2 levels and changing precipitation patterns. We found that by separating out the VPD effect from rising temperatures, VPD increases had a greater negative impact on yield (12.9 ± 1.8%, increase in VPD associated with 2 °C warming) compared to that from warming (8.5 ± 1.4%, the direct effect of 2 °C warming). The negative impact of these two factors varied with precipitation levels and influenced yield through separate mechanisms. Warmer temperatures caused yield loss mainly through shortening the growing season, while elevated VPD increased water loss and triggered several water stress responses such as reduced photosynthetic rates, lowered leaf area development, and shortened growing season length. Elevated CO2 concentrations partially alleviated yield loss under warming or increased VPD conditions through water savings, but the impact level varied with precipitation levels and was most pronounced under drier conditions. These results demonstrate the key role VPD plays in crop growth and yield, displaying a magnitude of impact comparative to temperature and CO2. A mechanistic understanding of the function of VPD and its relation with other climate factors and management practices is critical to improving crop yield projections under a changing climate.

Transcriptomic Responses to Water Deficit and Nematode Infection in Mycorrhizal Tomato Roots.

Climate changes include the intensification of drought in many parts of the world, increasing its frequency, severity and duration. However, under natural conditions, environmental stresses do not occur alone, and, in addition, more stressed plants may become more susceptible to attacks by pests and pathogens. Studies on the impact of the arbuscular mycorrhizal (AM) symbiosis on tomato response to water deficit showed that several drought-responsive genes are differentially regulated in AM-colonized tomato plants (roots and leaves) during water deficit. To date, global changes in mycorrhizal tomato root transcripts under water stress conditions have not been yet investigated. Here, changes in root transcriptome in the presence of an AM fungus, with or without water stress (WS) application, have been evaluated in a commercial tomato cultivar already investigated for the water stress response during AM symbiosis. Since root-knot nematodes (RKNs, Meloidogyne incognita) are obligate endoparasites and cause severe yield losses in tomato, the impact of the AM fungal colonization on RKN infection at 7 days post-inoculation was also evaluated. Results offer new information about the response to AM symbiosis, highlighting a functional redundancy for several tomato gene families, as well as on the tomato and fungal genes involved in WS response during symbiosis, underlying the role of the AM fungus. Changes in the expression of tomato genes related to nematode infection during AM symbiosis highlight a role of AM colonization in triggering defense responses against RKN in tomato. Overall, new datasets on the tomato response to an abiotic and biotic stress during AM symbiosis have been obtained, providing useful data for further researches.

Combining genome-wide and transcriptome-wide analyses reveal the evolutionary conservation and functional diversity of aquaporins in cotton

BackgroundAquaporins (AQPs) are integral membrane proteins from a larger family of major intrinsic proteins (MIPs) and function in a huge variety of processes such as water transport, plant growth and stress response. The availability of the whole-genome data of different cotton species allows us to study systematic evolution and function of cotton AQPs on a genome-wide level.ResultsHere, a total of 53, 58, 113 and 111 AQP genes were identified in G. arboreum, G. raimondii, G. hirsutum and G. barbadense, respectively. A comprehensive analysis of cotton AQPs, involved in exon/intron structure, functional domains, phylogenetic relationships and gene duplications, divided these AQPs into five subfamilies (PIP, NIP, SIP, TIP and XIP). Comparative genome analysis among 30 species from algae to angiosperm as well as common tandem duplication events in 24 well-studied plants further revealed the evolutionary conservation of AQP family in the organism kingdom. Combining transcriptome analysis and Quantitative Real-time PCR (qRT-PCR) verification, most AQPs exhibited tissue-specific expression patterns both in G. raimondii and G. hirsutum. Meanwhile, a bias of time to peak expression of several AQPs was also detected after treating G. davidsonii and G. hirsutum with 200 mM NaCl. It is interesting that both PIP1;4 h/i/j and PIP2;2a/e showed the highly conserved tandem structure, but differentially contributed to tissue development and stress response in different cotton species.ConclusionsThese results demonstrated that cotton AQPs were structural conservation while experienced the functional differentiation during the process of evolution and domestication. This study will further broaden our insights into the evolution and functional elucidation of AQP gene family in cotton.

Water stress during the post-harvest period affects new root formation but not starch concentration and content in Chardonnay grapevine (Vitis vinifera L.) perennial organs

Water stress responses during the post-harvest period were evaluated in a Chardonnay container-grown grapevines grafted onto 1103 Paulsen rootstock. The irrigation treatments were: a control treatment (C) (irrigated to match ETC demands) and a water stress treatment (WS) (irrigated when midday stem water potential reached a -1.1 MPa threshold). Photosynthesis, biomass and carbohydrate content were determined on five vines in each treatment on specific dates, from harvest until leaf fall. Stressed vines reduced leaf area due to defoliation, while well-watered vines had a higher carbon accumulation allowing the formation of new roots during the post-harvest period. No dry biomass accumulation was observed in the shoot and trunk organs after fruit harvest. Starch concentration and content were not affected by water stress. At the end of the experiment, starch concentrations were lower in the shoots and trunk than in the roots. Water stress induced a variation on biomass accumulation between above and below ground perennial organs, with the roots being the main organs in which biomass and starch concentrations were accumulated and kept, respectively.

EFFECT OF WATER STRESS ON OKRA YIELD AT VEGETATIVE STAGE

This study was conducted in Technical College of Applied Sciences, Sulaimany Polytechnic University, during 2017. Different levels of irrigation were used to production of okra plant. Complete Randomize Design used to layout of the experiment, with three level of irrigation in four replications. Yield, fresh weight of plant, dry weight of plant, yield response factor and different levels of irrigation were observed. The highest yield was given from treatment T1 (3.17 t/ha.) and the lowest was given from T3 (2.988 t/ha.). Also, the maximum fresh weight and dry weight of plant were given from T1 (61.40, 11.218 t/ha.), and their minimum was given from treatment T3 (57.00, 8.783 t/ha.). The highest water use efficiency and harvest index were obtained from T3 (1.615 kg.m-3, 0.095), and the lowest was given from treatment T1 (1.055 kg.m-3, 0.094). The crop response factor and the results in this study showed that the okra plants have a good response of water stress. As a result, we can recommend cultivating the okra at that time without irrigation in that region.

Optimizing the riparian zone width near a river for controlling lateral migration of irrigation water and solutes

Riparian zones are essential to preserve water quality of rivers adjacent to large areas of irrigated agriculture. We used HYDRUS (2D/3D) to quantify the long-term (8 years) influence of crops (almonds, wine grapes and potato-carrot) irrigated with recycled water on water and solute exchange at the Gawler River interface in relation to vegetation buffer widths from 10 to 110 m. We found that under almond and annual horticulture the likely average annual water flow from the irrigated area to the river was nearly twice as much (2.1 and 1.8, respectively) that under wine grapes. The hydraulic exchange at river interface for different irrigated crops was found to be sensitive to the buffer widths. For wine grapes, almonds and annual horticulture, the average annual hydraulic balance reached an equilibrium at 20, 65 and 55 m buffer widths, respectively. Furthermore, for wine grapes, with a 20 m buffer width, the average annual load of salts became negligible. This study shows that buffer widths of 20, 60, and 40 m for irrigated wine grapes, almond, and annual horticulture, respectively, are needed to restrict the migration of salts to the river. Further refinements are possible by incorporating the influence of preferential flow paths, improved water stress response functions, and addressing the data limitations for calibration of the model for solute dynamics.

Differential co-expression networks of long non-coding RNAs and mRNAs in Cleistogenes songorica under water stress and during recovery

BackgroundWater stress seriously constrains plant growth and yield. Long non-coding RNAs (lncRNAs) serve as versatile regulators in various biological regulatory processes. To date, the systematic screening and potential functions of lncRNA have not yet been characterized in Cleistogenes songorica, especially under water stress conditions.ResultsIn this study, we obtained the root and shoot transcriptomes of young C. songorica plants subjected to different degrees of water stress and recovery treatments by Illumina-based RNA-seq. A total of 3397 lncRNAs were identified through bioinformatics analysis. LncRNA differential expression analysis indicated that the higher response of roots compared to shoots during water stress and recovery. We further identified the 1644 transcription factors, 189 of which were corresponded to 163 lncRNAs in C. songorica. Though comparative analyses with major Poaceae species based on blast, 81 water stress-related orthologues regulated to lncRNAs were identified as a core of evolutionary conserved genes important to regulate water stress responses in the family. Among these target genes, two genes were found to be involved in the abscisic acid (ABA) signalling pathway, and four genes were enriched for starch and sucrose metabolism. Additionally, the 52 lncRNAs were predicted as target mimics for microRNAs (miRNAs) in C. songorica. RT-qPCR results suggested that MSTRG.43964.1 and MSTRG.4400.2 may regulate the expression of miRNA397 and miRNA166, respectively, as target mimics under water stress and during recovery. Finally, a co-expression network was constructed based on the lncRNAs, miRNAs, protein-coding genes (PCgenes) and transcription factors under water stress and during recovery in C. songorica.ConclusionsIn C. songorica, lncRNAs, miRNAs, PCgenes and transcription factors constitute a complex transcriptional regulatory network which lncRNAs can regulate PCgenes and miRNAs under water stress and recovery. This study provides fundamental resources to deepen our knowledge on lncRNAs during ubiquitous water stress.

Optical Flow-Based Analysis of the Relationships between Leaf Wilting and Stem Diameter Variations in Tomato Plants.

The estimation of water stress is critical for the reliable production of high-quality fruits cultivated using the tacit knowledge of expert farmers. Multimodal deep neural network has achieved success in the estimation of stem diameter variations as a water stress index, calculated from leaf wilting and environmental data. However, these studies have not addressed the specific role of leaf wilting in the estimation. Revealing the role of leaf wilting not only ensures the reliability of the estimation model but also provides an opportunity for improving the estimation method. In this paper, we investigated the relationships between leaf wilting and stem diameter variations without resorting to black-box approaches such as deep neural network. To clarify the role of leaf wilting, this study uses cross-correlation analysis to analyze the time lag correlation between leaf wilting, quantified by optical flow, and stem diameter variations as a water stress index. The analysis showed that leaf wilting had a significant time lag correlation with short-term stem diameter variations, which were water stress responses in plants. As the results were consistent with known plant water transport mechanisms, it was suggested that leaf wilting quantified by optical flow can explain short-term stem diameter variations.

High‐Throughput Field Phenotyping to Assess Irrigation Treatment Effects in Quinoa

Core Ideas Water stress in multiple quinoa varieties were introduced. Remote sensing technologies were evaluated to assess water stress response. Handheld and unmanned aerial system based sensors provided reliable data. Thermal imaging data could capture stress in quinoa varieties. Quinoa (Chenopodium quinoa Willd.) is a crop known for its tolerance to abiotic stress such as drought and salinity. Quinoa is also a versatile superfood, which is gluten‐free and high in protein, vitamins, nutrients, and beneficial antioxidants. Washington State University's quinoa breeding program efforts focus on identification and development of varieties that are resilient to local environmental conditions. In this study, high‐throughput phenotyping techniques were applied to evaluate the performance of quinoa varieties under different irrigation regimes. Handheld multispectral radiometer (Crop Scan), proximal sensing system using ground platform, and remote sensing with unmanned aerial system (UAS) were used to assess the performance of eight quinoa varieties under two irrigation treatments (non‐irrigated and irrigated). Crop Scan data, along with multispectral and thermal infrared images, were acquired at multiple time points at different stages of crop development during the season. In general, the normalized difference vegetation index, water band index, and green normalized difference vegetation index (GNDVI) data extracted from Crop Scan, and GNDVI and canopy temperature data extracted from UAS were able to detect irrigation treatment effects. Comparing the spectral data acquired at multiple scales indicated that Crop Scan data were highly and significantly correlated with remote sensing data (|r| = 0.57–0.85). Rapid data acquisition and the ability to detect differences among varieties under water stress highlight the application of remote sensing techniques as a high‐throughput phenotyping tool to evaluate quinoa.

Stress tolerance indices based on yield, phenology and biomass partitioning: A review

Breeding for water stress tolerance is very difficult as the stress conditions created in experimental set up and actual field conditions, invariably, have poor correspondence. Direct selection for yield under stress holds promise but is slow on account of complexity of yield. Screening based on yield suffers from low heritability. Yield has been the primary breeding objective in production breeding and has been improved either by targeting yield per se as well as yield components based on correlated response. Drought stress indices are quantitative measures that characterize water stress response by yield data from one or several environments based on timing, duration and intensity of stress. Such an index is more readily useable than raw yield data. Since drought resistance is a yield based trait, selection could vary depending on which index is chosen by the breeder. A major drawback of using these indices has been lack of correspondence in rankings across indices and their failure to discriminate overlapping responses in terms of yield under stress. There has been substantial effort on part of scientists to develop and validated different indices based on yield per se, index scores, regression analysis as well as various model based approaches. The major focus has been on identifying variables such as phenology, physiological traits, biomass partitioning or other parameters that influence crop performance under stress. The paper appraises the approaches from yield based indices to regression based as well as crop model based that have been used to understand crop response to water stress.

Excessive soil water stress responses of sesame (Sesamum indicum L.) and perilla (Perilla frutescens L.) cultivated from paddy fields with different topographic features

Excessive soil water stress responses of sesame (Sesamum indicum L.) and perilla (Perilla frutescens L.) cultivated from paddy fields with different topographic features

Effects of anesthesia and salt treatment on stress responses, and immunological and hydromineral characteristics of common carp (Cyprinus carpio, Linnaeus, 1758) subjected to transportation

The aim of the present study was to investigate the effects of anesthesia or salt treatment on stress responses, and immunological and hydromineral characteristics of common carp (Cyprinus carpio). The fish were either transported (5 h) either directly (control), following anesthesia (AN) or with salt addition to transportation tank water (SLT). Transportation was carried out in plastic bags supplied with pure oxygen. The control fish were directly transferred from a holding aquarium to the transportation bags. The fish of AN group were first anesthetized (100 mg/L eugenol for 90 s) in their holding aquaria, then transferred to the transportation bags. The fish of the SLT group were directly transferred to the transportation bags containing 3 g/L salt. Blood samples were taken before and 0, 1, 2 and 3 days after the 5-h transportation. Results showed that salt treatment mitigated decrease in water pH and dissolved oxygen and increase in water ammonia levels. Transportation led to increase in serum cortisol, glucose and calcium levels, and decrease in serum lactate, sodium, chloride, lysozyme, alternative complement (ACH50) and total immunoglobulin (Ig). Salt treatment mitigated stress responses and inhibited hydromineral disturbance and immunosuppression after transportation. Pre-transportation anesthesia negligibly counteracted the adverse effects of transportation on water unionized ammonia, and serum chloride levels. In conclusion, addition of 3 g/L salt to transportation water seems to be beneficial for common carp as it mitigates water quality deterioration, stress responses, hydromineral imbalance and immunosuppression.

Can Faba Bean Physiological Responses Stem from Contrasting Traffic Management Regimes?

Our study examined how faba beans (Vicia faba L.) grown in soil conditions that simulate common traffic management regimes and water availabilities displayed alterations to their physiological state. Physiological changes were tracked through plant and sensor-based measurements, such as evapotranspiration, water use efficiency, aboveground biomass, stomatal conductance, and normalized difference vegetation index. A greenhouse experiment comprised of faba beans were sown into pots of two different soil types that were separated by treatments of dry bulk density and volumetric water content. The compaction treatment with a bulk density of 1.2 g cm−3 coupled with a volumetric water content of 41% displayed more favorable changes to the physiological state of the faba beans than the contrasting treatment of 1.4 g cm−3 bulk density at 33% volumetric water content. Handheld sensor-based measurements, such as the normalized difference vegetation index, exhibited a strong correlation with faba bean biomass production. Furthermore, the stomatal conductance was able to reveal plant water stress and capture evapotranspiration responses. Conclusive observations showed that increasing soil compaction restricted plant productivity. However, the presence of high water content was shown to offset the negative effects of heavily applied compaction while relatively lower water contents exacerbated differences in plant responses across compaction treatments.

Conformational plasticity of the intrinsically disordered protein ASR1 modulates its function as a drought stress-responsive gene.

Plants in arid zones are constantly exposed to drought stress. The ASR protein family (Abscisic, Stress, Ripening) -a subgroup of the late embryogenesis abundant superfamily- is involved in the water stress response and adaptation to dry environments. Tomato ASR1, as well as other members of this family, is an intrinsically disordered protein (IDP) that functions as a transcription factor and a chaperone. Here we employed different biophysical techniques to perform a deep in vitro characterization of ASR1 as an IDP and showed how both environmental factors and in vivo targets modulate its folding. We report that ASR1 adopts different conformations such as α-helix or polyproline type II in response to environmental changes. Low temperatures and low pH promote the polyproline type II conformation (PII). While NaCl increases PII content and slightly destabilizes α-helix conformation, PEG and glycerol have an important stabilizing effect of α-helix conformation. The binding of Zn2+in the low micromolar range promotes α-helix folding, while extra Zn2+ results in homo-dimerization. The ASR1-DNA binding is sequence specific and dependent on Zn2+. ASR1 chaperone activity does not change upon the structure induction triggered by the addition of Zn2+. Furthermore, trehalose, which has no effect on the ASR1 structure by itself, showed a synergistic effect on the ASR1-driven heat shock protection towards the reporter enzyme citrate synthase (CS). These observations prompted the development of a FRET reporter to sense ASR1 folding in vivo. Its performance was confirmed in Escherichia coli under saline and osmotic stress conditions, representing a promising probe to be used in plant cells. Overall, this work supports the notion that ASR1 plasticity is a key feature that facilitates its response to drought stress and its interaction with specific targets.

Influence of fungal endophytes on plant physiology is more pronounced under stress than well-watered conditions: a meta-analysis.

A meta-analysis of published articles shows that the influence of fungal endophytes on plant performance is dependent on plant water status. The magnitude of endophytic effects is higher in plants grown in water-limiting environments than those in adequate watering environments. The outcome of plant-endophyte interactions depends on the identity of the plant host and fungal symbionts. Water limitation often hinders plant productivity in both natural and agricultural settings. Endophytic fungal symbionts can mediate plant water stress responses by enhancing drought tolerance and avoidance, but these effects have not been quantified across plant-endophyte studies. A meta-analysis of published studies was performed to determine how endophytic fungal symbionts influence plant response under non-stressed versus water-stressed conditions. A significantly positive or neutral overall effect of fungal endophyte was noted under water-stressed conditions. In contrast, under non-stressed conditions, the overall effect of fungi on plants was mostly neutral. In general, the presence of fungal endophytes increased plant's total biomass, chlorophyll content, and stomatal conductance irrespective of water availability. In addition, plant shoot biomass, tiller density, plant height, maximum quantum yield (Fv/Fm), net photosynthesis, relative water content (RWC), amounts of ascorbate peroxidase (APX), glutathione (GSH), polyphenol oxidase (PPO), superoxide dismutase (SOD), and phenolics were significantly increased by endophyte colonisation under stressed conditions. Malondialdehyde (MDA) and hydrogen peroxide (H2O2) were reduced in endophytic plants under stress as compared with non-endophytic counterparts. Categorical analysis revealed that accumulation in plant biomass is influenced by factors such as host and fungi identity, the magnitude of which is greater under stressed than non-stressed conditions.

Impact of zinc on dehydration and rehydration responses in tea

Zinc nutrition of tea (Camelia sinensis) have a great impact on acclimation to dehydration stress and on improvement of stress recovery. Dehydration stress induced by withholding water for 7 d decreased relative water content, dry mass of leaf, and content of antioxidants like ascorbate and glutathione and increased H2O2 content and lipid peroxidation and changed activities of superoxide dismutase, catalase, peroxidase, and glutathione reductase. A pre-treatment with 0.1 and 0.5 mM ZnSO4 minimized these effects and increased Zn uptake. Further, foliar spray with 0.1 and 0.5 mM ZnSO4 before rehydration lowered H2O2 generation, increased content of antioxidants and activities of antioxidative enzymes, and decreased lipid peroxidation. The present findings suggest that zinc regulates water stress responses and recovery after rehydration in tea.