Reduction In Relative Water Content Research Articles

Prediction and validation of DREB transcription factors for salt tolerance in Solanum lycopersicum L.: An integrated experimental and computational approach

The dehydration responsive element binding (DREB) transcription factors (TFs) have been intensely reported to regulate plant growth and defence response under stress condition. In this study, we have investigated impact of salt stress (400 mM) at vegetative stage in tomato hybrids on (1) several yield and related components (2) relative water content, membrane stability (3) enzymatic activity and gene expression levels of stress responsive genesand since in tomato, little is known about its functional binding motifs, protein-protein interactions and core amino acid residues involved in the regulation of its expression under stress condition (4)we also used in silico approach to structurally and functionally characterize tomato DREB1 protein in response to salt stress. Salt stress imposed at vegetative stage caused significant reduction in relative water content, chlorophyll content, proline content, expression of stress responsive genes and enhanced membrane damage in all the hybrids. However, hybrids viz., VRTH-1754 and VRTH-1755 showed remarkable tolerance to salt stress as they showed low membrane damage, increased proline content and enhanced activity of antioxidant enzyme along with expression of stress responsive genes. Phylogenetic foot-printing, multiple sequence alignment, and motif analysis of S. lycopersicum DREB1 (SlDREB1) reveal remarkable similarities with its wild homologue showing monophyletic origin with S. pimpinellifolium and close relation with S. pennelli and S. tuberosum. Additionally, DNA-protein interaction study revealed that the SlDREB1 protein binds to Dehydration Responsive Element (DRE) DNA element through conserved KYRG region of AP2/ERF domain with flanking sequences viz., Tyr49, Gly50, Pro51, Cys52, and Arg54.Furthermore, gene ontology (GO) analysis predicted the most significant subcellular localization of SlDREB1 protein to the chloroplast (32.9%) followed by nucleus (28.9%) and cytoplasm (17.6%) revealing that SlDREB1 proteins were mainly involved in ethylene mediated signalling pathway, transcription initiation and defence response.

Differential characterization of physiological and biochemical responses during drought stress in finger millet varieties

Drought is the most perilous abiotic stress that affects finger millet growth and productivity worldwide. For the successful production of finger millet, selection of drought tolerant varieties is necessary and critical stages under drought stress, germination and early seedling growth, ought to be fully understood. This study investigated the physiological and biochemical responses of six finger millet varieties (GBK043137, GBK043128, GBK043124, GBK043122, GBK043094 and GBK043050) under mannitol-induced drought stress. Seeds were germinated in sterile soil and irrigated with various concentrations of mannitol (200, 400 and 600mM) for 2weeks. In a comparative analysis relative water content (RWC), chlorophyll, proline and malondialdehyde (MDA) contents were measured to obtain the physiological and biochemical characteristics of drought stress. The results showed that increased levels of drought stress seriously decreased germination and early seedling growth of finger millet varieties. However, root growth was increased. In addition, exposition to drought stress triggered a significant decrease in relative water content and chlorophyll content reduction, and the biochemical parameters assay showed less reduction in RWC. Furthermore, oxidative damage indicating parameters, such as proline concentration and MDA content, increased. Varieties GBK043137 and GBK043094 were less affected by drought than the other varieties as shown by significant changes in their physiological parameters. Our findings reveal the differences between the physiological and biochemical responses of finger millet to drought and are vital for breeding and selecting drought tolerant varieties of finger millet. Further, genomic and molecular investigations need to be undertakento gain a deeper insight into the detailed mechanisms of drought tolerance in finger millet.

Effect of nitrogen application on the phytochemical production in Jatropha curcas L. (Angiosperms: Euphorbiaceae) during drought conditions

Nitrogen is an important nutrient for the successful metabolism of plants, but its occurrence in soil is always very limited. This nutrient has a significant role to preserve plants during various stress conditions by altering the production rate of phytochemicals as defense weapons. Hence, this study was carried out to analyze the effect of nitrogen supply on the phytochemical composition and relative water content in Jatropha curcas L. under a simulated drought condition. The selected seedlings were grown from stem cuttings and categorized into different treated three groups along with the control. After the completion of the experiment, the growth pattern and phytochemical production were investigated. An increased malondialdehyde activity (MDA) was reported with a reduction in relative water content (RWC) of the leaf and in the biomass of seedlings under drought stress. A significant decrease in the levels of alkaloids, phenol, flavonoids and tannins with an increase in saponins and terpenoids was also observed in only simulated drought stressed plants. While a significant increase in the levels of total alkaloid, tannins, flavonoids and phenols was observed in those plants where exogenous nitrogen was supplied before the start of drought periods, unlike in treated and control plants. Therefore, it was revealed that application of Nitrogen enabled the plants to possess protective mechanism through the production of phytochemicals that facilitate the cell membrane to reduce the detrimental effects caused by drought stress.

Pathogenesis of mulberry leaf spot in response to meteorological aspects of Kashmir, India

In this study, the influence of climatic factors on the development of leaf spot diseases of mulberry (Morus alba L.) in Kashmir, India was studied. It was found that the highest disease incidence and severity of Goshoerami variety was found in tree type (13.86% and 1.98%) followed by dwarf (7.53% and 1.67%) and bush (3.38% and 0.99%), respectively. Due to infection of pathogen, the relative water content and chlorophyll content of leaves were consistently decreased. The order of reduction in relative water content of infected leaves was found as: bush > dwarf > tree, while as the reduction in chlorophyll content: bush > tree > dwarf. It was also found that temperature of 25–30 °C and relative humidity of above 80% favoured the development of the disease. Rapid development of disease was found during the month of June, July and August when average temperature and relative humidity was about 25–30°C and 80%, respectively.

Growth, Physiological, Biochemical, and Transcriptional Responses to Drought Stress in Seedlings of Medicago sativa L., Medicago arborea L. and Their Hybrid (Alborea)

Medicago sativa L. is a tetraploid perennial forage legume of great agronomical interest. The increasing need for its use under water-deficit conditions as well as low-input systems demands further improvement of its drought tolerance. On the other hand, Medicagoarborea L. is a perennial leguminous shrub, which is knownas a drought-tolerant species. In the present study, drought stress responses of the aforementioned medicago species, along with their hybrid, named Alborea, were comparatively assayed at the morphological, physiological, biochemical, and transcriptional levels. In particular, transcript abundance of representative genes that: (a) control ion transport, intracellular Na+/H+ antiporters(NHX1) and rare cold inducible2A (RCI2A); (b) have an osmotic function Δ1-pyrroline-5-carboxylate synthetase 1 (P5CS1); and (c) participate in signaling pathways and control cell growth and leaf function stress-induced mitogen-activated protein kinases kinases (SIMKK), Zinc Finger (ZFN), apetala2/ethylene-responsive element binding (AP2/EREB), basic leucine zipper (bzip) and Medicago sativa Helicase 1(MH1) were evaluated. Under well-watered conditions, the studied population of Alborea showed the highest stem elongation rate and photosynthetic rate that were dramatically reduced under drought conditions compared to M. sativa and M. arborea. Under drought conditions, the studied population of M. arborea showed less reduction of relative water content, all gas-exchange parameters, less lipid peroxidation, and more antioxidant capacity. Moreover, transcriptional analysis demonstrated that the population of M. arborea exhibited significantly higher transcript levels of drought-responsive genes in both leaves and roots under drought stress conditions. M. sativa has better antioxidant capacity than Alborea and had a higher induction of stress-related genes, thus it performs better than Alborea under drought conditions. Among the studied genes, it seems that AP2/EREB play a critical role in the response of the studied population to drought stress.

Physiological and biochemical response of cowpea (Vigna unguiculata L.) landraces of Kashmir valley under water stress

The present study is based on the hypothesis that natural variation for physiological and biochemical parameters can be effectively harnessed to improve water stress resilience. Under irrigated conditions, CTD decreased progressively. However, under drought stress, it decreased sharply. Under drought relative water content (RWC) had a mean value of 65.49% with the highest and lowest value recorded for C25 and C32. The largest and smallest reduction in RWC under drought was recorded in case of C32 and C9. There was wide variation in chlorophyll a and b content. The highest and lowest values for chlorophyll stability index (CSI) were recorded for C13 and C29 respectively. The DAB assay clearly differentiated the lines on the basis of darker staining of leaves. The lines showing greater per cent reductions in yield parameters such as C1, C2, C3, C7, C12, C14, C22 and C29 showed greater staining in leaves in DAB assay.

The growth impairment of salinized fenugreek (Trigonella foenum-graecum L.) plants is associated to changes in the hormonal balance

Fenugreek is a legume cultivated for its medicinal value, especially in arid and semi-arid regions, where soil salinity is an increasing problem. In fact, salinity is one of the major environmental factors limiting plant growth and productivity. Plant hormones are known to play vital roles in the ability of the plants to acclimatize to varying environments by mediating growth, development, and nutrient allocation. Thus, to gain insights about the role of plant hormones in the growth responses of salinized fenugreek plants (Trigonella foenum-graecum L.), a medium-term experiment was conducted under moderate (100 mM NaCl) and high (200 mM NaCl) salinity levels. Results showed that moderate, but especially high salinity stress, impaired shoot growth, total leaf area and leaf number. Salinity also provoked a reduction in relative water content, stomatal conductance and photosynthesis-related pigments, but, surprisingly, photosynthetic rate increased in the leaves of fenugreek plants. Na accumulated in the leaves, particularly at high salinity levels, while most mineral nutrients decreased. Furthermore, important changes in the main hormone classes were observed, associated to growth reduction under salinity. The active cytokinin form, trans-zeatin, and active cytokinin and gibberellin concentrations decreased with salinity in the leaves of fenugreek plants, whereas the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid, accumulated in the roots of fenugreek plants, especially at high salinity levels. Importantly, leaf abscisic acid concentrations increased under salinity, which could limit leaf transpiration to adapt growth to the stressful conditions. Therefore, plant hormones seem to play a critical role in the growth responses of fenugreek plants under salinity stress and they could have potential interest in salt tolerance programmes for this species.

Ecophysiological Responses of Calcicole Cyclobalanopsis glauca (Thunb.) Oerst. to Drought Stress and Calcium Supply

Water deficit and high calcium (Ca2+) content and are two typical soil characteristics in the Karst region. However, the problem of whether high Ca2+ in Karst calcareous soil could increase drought tolerance in calcicole plants has not been solved. We investigated the ecophysiological responses of Cyclobalanopsis glauca (Thunb.) Oerst. cuttings to short-term drought stress and Ca2+ application. Drought stress (10% PEG-6000) markedly reduced relative water content (RWC) and water potential (WP), and enhanced the levels of reactive oxygen species (ROS) production (H2O2 and O2•−) and malondialdehyde (MDA) content in C. glauca leaves. Under drought treatment, exogenous Ca2+ application (20 mM CaCl2) markedly increased the RWC and WP, and reduced the H2O2, O2•−, and MDA content. Furthermore, water deficit induced a significant increase in the activities of antioxidant enzymes such as peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), and glutathione peroxidase (GPX), and increased the accumulation of osmoregulation substances. External Ca2+ alleviated drought-induced oxidative stress and osmotic stress with further increased activities of antioxidant enzymes, and enhanced the accumulation of osmoregulation substances. In addition, exogenous Ca2+ treatment alleviated the reduction of the photosynthesis rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and chlorophyll content (SPAD), and further increased water use efficiency (WUE) under drought stress. This study confirms that exogenouos Ca2+ application induces improvements in the water status, osmotic adjustment, antioxidant defense, and photosynthesis efficiency of C. glauca under drought stress.

The Mitochondrial Thioredoxin System Contributes to the Metabolic Responses Under Drought Episodes in Arabidopsis.

Thioredoxins (Trxs) modulate metabolic responses during stress conditions; however, the mechanisms governing the responses of plants subjected to multiple drought events and the role of Trxs under these conditions are not well understood. Here we explored the significance of the mitochondrial Trx system in Arabidopsis following exposure to single and repeated drought events. We analyzed the previously characterized NADPH-dependent Trx reductase A and B double mutant (ntra ntrb) and two independent mitochondrial thioredoxin o1 (trxo1) mutant lines. Following similar reductions in relative water content (∼50%), Trx mutants subjected to two drought cycles displayed a significantly higher maximum quantum efficiency (Fv/Fm) and were less sensitive to drought than their wild-type counterparts and than all genotypes subjected to a single drought event. Trx mutant plants displayed a faster recovery after two cycles of drought, as observed by the higher accumulation of secondary metabolites and higher stomatal conductance. Our results indicate that plants exposed to multiple drought cycles are able to modulate their subsequent metabolic and physiological response, suggesting the occurrence of an exquisite acclimation in stressed Arabidopsis plants. Moreover, this differential acclimation involves the participation of a set of metabolic changes as well as redox poise alteration following stress recovery.

Linking morphological and ecophysiological leaf traits to canopy dieback in Persian oak trees from central Zagros

Intraspecific variability in morphological and ecophysiological leaf traits might be theorized to be present in declining populations, since they seem to be exposed to stress and plasticity could be advantageous. Here we focused on declining Persian oaks (Quercus brantii Lindl. var. persica (Jaub and Spach) Zohary) in the Zagros Mountains of western Iran, representing the most important tree species of this region. We selected trees with contrasting crown dieback, from healthy to severely defoliated, to investigate the relationships between canopy dieback and leaf morphology, water content and pigments. We also measured esterase and peroxidase, as enzymatic antioxidants and indicators of contrasting genotypes. Trees showing moderate to severe defoliation showed higher leaf mass area (LMA), reduced relative water content (RWC), and lower stomatal density (SD). Increasing LMA indicates a more sclerophyllic structure, according to drier conditions. We did not find significant differences in leaf pigments (chlorophyll a and b, and carotenoids) among crown dieback classes, suggesting that Persian oak trees are able to maintain accurate photochemical efficiency, while reduced RWC and SD suggest hydraulic limitations. Our results do not provide a consistent pattern as regards enzymatic antioxidant defense in Persian oak. Morphological leaf traits would be important drivers of future adaptive evolution in Persian oak, leading to smaller and thicker leaves, which have fitness benefits in dry environments. Nonetheless, drought responses may be critically affecting carbon uptake, as photosynthetic compounds are less effectively used in leaves with higher sclerophylly.

Carbon (δ13C) and Nitrogen (δ15N) Stable Isotope Composition Provide New Insights into Phenotypic Plasticity in Broad Leaf Weed Rumex acetosa under Allelochemical Stress

Phenolic compounds, hydroquinone and cinnamic acid derivatives have been identified as major allelochemicals with known phytotoxicity from allelopathic plant Acacia melanoxylon R. Br. Several phenolic compounds such as ferulic acid (FA), p-hydroxybenzoic acid (pHBA) and flavonoid (rutin, quercetin) constituents occur in the phyllodes and flowers of A. melanoxylon and have demonstrated inhibitory effects on germination and physiological characteristics of lettuce and perennial grasses. However, to date, little is known about the mechanisms of action of these secondary metabolites in broad-leaved weeds at ecophysiological level. The objective of this study was to determine the response of Rumex acetosa carbon isotope composition and other physiological parameters to the interaction of plant secondary metabolites (PSM) (FA and pHBA) stress and the usefulness of carbon isotope discrimination (Δ13C) as indicative of the functional performance of intrinsic water use efficiency (iWUE) at level of plant leaf. R. acetosa plant were grown under greenhouse condition and subjected to PSM stress (0, 0.1, 0.5, 1.0, and 1.5 mM) for six days. Here, we show that FA and pHBA are potent inhibitors of Δ13C that varied from 21.0‰ to 22.9‰. Higher pHBA and FA supply enhanced/retard the Nleaf and increased the Cleaf while ratio of intercellular CO2 concentration from leaf to air (Ci/Ca) was significantly decreased as compared to control. Leaf water content and leaf osmotic potential were decreased following treatment with both PSM. The Ci/Ca decreased rapidly with higher concentration of FA and pHBA. However, iWUE increased at all allelochemical concentrations. At the whole plant level, both PSM showed pronounced growth-inhibitory effects on PBM and C and N concentration, root fresh/dry weight, leaf fresh/dry weight, and root, shoot length of C3 broad leaf weed R. acetosa. Carbon isotope discrimination (Δ) was correlated with the dry matter to transpiration ratio (transpiration efficiency) in this C3 species, but its heritability and relationship to R. acetosa growth are less clear. Our FA and pHBA compounds are the potent and selective carbon isotope composition (δ13C) inhibitors known to date. These results confirm the phytotoxicity of FA and pHBA on R. acetosa seedlings, the reduction of relative water content and the induction of carbon isotope discrimination (Δ) with lower plant biomass.

Overexpression of a NF-YC Gene Results in Enhanced Drought and Salt Tolerance in Transgenic Seashore Paspalum.

Seashore paspalum (Paspalum vaginatum O. Swartz) is an important warm-season turfgrass species. In this study we generated transgenic seashore paspalum overexpressing CdtNF-YC1, a nuclear factor Y transcription factor from hybrid bermudagrass (Cynodon dactylon × Cynodon transvaalensis). DNA blot hybridization and qRT-PCR analysis showed that CdtNF-YC1 was integrated into the genomes of transgenic seashore paspalum plants and expressed. Reduced relative water content (RWC) and survival rate and increased ion leakage were observed in both wild type (WT) and transgenic plants after drought stress, while transgenic plants had higher levels of RWC and survival rate and lower ion leakage than the WT. Maximal photochemical efficiency of photosystem II (Fv/Fm), chlorophyll concentration and survival rate were decreased after salt stress, while higher levels were maintained in transgenic plants than in WT. In addition, an increased Na+ content and decreased or unaltered K+ in leaves and roots were observed after salt treatment, while lower level of Na+ and higher levels of K+ and K+/ Na+ ratio were maintained in transgenic plants than in WT. The results indicated that overexpressing CdtNF-YC1 resulted in enhanced drought and salt tolerance in transgenic plants. Transcript levels of stress responsive genes including PvLEA3, PvP5CS1, PvABI2, and PvDREB1B were induced in response to drought and salt stress, and higher levels were observed in transgenic seashore paspalum than in WT. The results suggest that the enhanced drought and salt tolerance in transgenic seashore paspalum is associated with induction of a series of stress responsive genes as a result of overexpression of CdtNF-YC1.

Insight into salt tolerance mechanisms of the halophyte Achras sapota: an important fruit tree for agriculture in coastal areas

Sapota (Achras sapota), a fruit tree with nutritional and medicinal properties, is known to thrive in salt-affected areas. However, the underlying mechanisms that allow sapota to adapt to saline environment are yet to be explored. Here, we examined various morphological, physiological, and biochemical features of sapota under a gradient of seawater (0, 4, 8, and 12 dS m-1) to study its adaptive responses against salinity. Our results showed that seawater-induced salinity negatively impacted on growth-related attributes, such as plant height, root length, leaf area, and dry biomass in a dose-dependent manner. This growth reduction was positively correlated with reductions in relative water content, stomatal conductance, xylem exudation rate, and chlorophyll, carbohydrate, and protein contents. However, the salt tolerance index did not decline in proportional to the increasing doses of seawater, indicating a salt tolerance capacity of sapota. Under salt stress, ion analysis revealed that Na+ mainly retained in roots, whereas K+ and Ca2+ were more highly accumulated in leaves than in roots, suggesting a potential mechanism in restricting transport of excessive Na+ to leaves to facilitate the uptake of other essential minerals. Sapota plants also maintained an improved leaf succulence with increasing levels of seawater. Furthermore, increased accumulations of proline, total amino acids, soluble sugars, and reducing sugars suggested an enhanced osmoprotective capacity of sapota to overcome salinity-induced osmotic stress. Our results demonstrate that the salt adaptation strategy of sapota is attributed to increased leaf succulence, selective transport of minerals, efficient Na+ retention in roots, and accumulation of compatible solutes.

Physiological, biochemical, and molecular responses of thermotolerance in moth bean (Vignaaconitifolia (Jacq.) Marechal)

Among several abiotic stresses, heat stress has a large negative impact upon agricultural productivity worldwide. Moth bean ( Vigna aconitifolia (Jacq.) Marechal) attracts a great deal of attention due to its better performance under drought and heat stress conditions. An experiment was designed to find out the effects of heat stress on relative water content (RWC), membrane stability index (MSI), and proline, protein, and chlorophyll (Chl) contents using 10 genotypes of moth bean. Physiological and biochemical parameters indicated that RMO 40 followed by Jadia, IC 36157, Jwala, and Marumoth were heat-tolerant (HT) genotypes, and IC 121051, IC 36392, IC 39702, IC 472257, and IC 140725 were heat-susceptible (HS) genotypes of moth bean. Under heat stress, the HT genotypes showed minimal reduction in RWC, MSI, and protein as compared to the susceptible ones, revealing that the HT genotypes performed well under heat stress. Many heat shock proteins and dehydration proteins are synthesized in plants under heat stress. Expression analysis of three such genes was performed in ten genotypes of moth bean. The analysis revealed that the HT genotypes showed better performance under stress conditions for survival. The above studied parameters would be very useful in the identification of HT varieties for future breeding programs in moth bean and related Vigna species.

Physiological responses of wheat to drought stress and its mitigation approaches

Drought is a polygenically controlled stress and a major agricultural risk that reduces crop productivity and limits the successful insight of land potential throughout the world. This review article has been divided into two parts, i.e., effect of drought stress on physiology of wheat and potential drought mitigation approaches. In the first part, physiological responses of wheat to stress were discussed. Cell membrane stability, relative water content, early maturity, decreased leaf area, small plant size, increased dry weight and root–shoot ratio, and the whole-plant transpiration rate response to enhanced atmospheric vapor pressure deficit are physiological traits associated with drought tolerance in wheat. Reduction of relative water content closes stomata and thereby reduces stomatal conductance. Osmotic adjustment improves drought tolerance by allowing cell enlargement, plant growth, and stomata to stay partially open and by maintaining CO2 fixation under severe water deficit. The wheat plant accumulates several organic and inorganic solutes in its cytosol to lessen its osmotic potential for maintenance of cell turgor. Drought affects photosynthesis negatively by changing the inner structure of chloroplasts, mitochondria, and chlorophyll content and minerals. Destruction of the photosystem II (PSII) oxygen releasing complex and reaction center can disturb production and use of electrons, causing lipid peroxidation of cell membrane through the production of reactive oxygen species. In the second part, drought mitigation approaches were discussed. Seed, drought, bacterial, and hormonal priming are common approaches used to lessen the effects of water deficit. Physiological trait-based breeding, molecular breeding, marker-assisted backcrossing, aerial phenotyping, water budgeting, and resource allocation are modern approaches used to develop drought tolerant wheat cultivars. Wheat genotypes produced as a result of a combination of all these methodologies will increase food security regarding the currently changing climate.

Effect of drought stress on water relation traits of four soybean genotypes

An experiment was conducted in a venyl house at the environmental stress site of Bangabandhu Sheikh Mujibur Rahman Agricultural University during September to December 2012 to know the internal water status under drought stress in soybean genotypes, viz. Shohag, BARI Soybean-6, BD2331 (relatively stress tolerant) and BGM2026 (susceptible). Drought (water) stress reduced the leaf water potential in all the genotypes though was more negative in tolerant genotypes than in susceptible ones. The lowest leaf water potential was obtained from BARI Soybean-6 (-1.58 MPa) and the highest in BGM2026 (-1.2 MPa). Relative water content (RWC) decreased remarkably in all the genotypes and reduction was more in susceptible than tolerant genotypes. At 8.00 am, RWC of stressed plants decreased by 9.58, 9.02, 8.90 and 13.90% in the genotype Shohag,, BARI Soybean-6, BD2331 and BGM2026 at vegetative stage, respectively. Drought stress decreased the exudation rate in all the genotypes of soybean and it was 24, 27, 22 and 12 mg h-1 in the genotype Shohag, BARI Soybean-6, BD2331 and BGM2026 at vegetative stage, respectively. Leaf temperatures in drought stressed plant were higher than in well-watered plants. Shohag, BARI Soybean-6, BD2331 and BGM2026 showed 4.7, 4.5 5.2 and 11.07% increase in leaf temperature due to water stress. At drought stressed treatment reduction in leaf water potential, relative water content, exudation rate and water retention capacity were noticed at the three growth stages in all the genotypes with a concurrent increase in leaf temperature. Genotypes BARI Soybean-6, Shohag and BD2331 showed considerably less reduction in relative water content, exudation rate and water retention capacity, high reduction in leaf water potential and less increase in leaf temperature during drought were considered as drought tolerant. However genotype BGM2026 showed considerably high reduction in relative water content, exudation rate and water retention capacity, low reduction in leaf water potential and high increase in leaf temperature was considered as drought susceptible.SAARC J. Agri., 15(2): 163-175 (2017)

Physiological, biochemical and yield responses of wheat cultivars to deficient water stress

Two similar and concurrent experiments were carried out in the Agricultural Research Center of Islamic Azad University, Kermanshah Branch and Agricultural Research Center of Islamabad during 2016-2017. The experiments were performed in a split-plot format in a randomized complete-block design based on 3 replications. The main plots were assigned to 4 different regimes of irrigation: (I1) full irrigation during the growth period followed by 50% of the soil moisture depletion; (I2) water deficit stress from the start of the flowering stage) Z61 (to the milking stage (Z77) associated with irrigation after 80% of the soil moisture depletion; (I3) water deficit stress from the beginning of the flowering stage(Z61) to the ripening stage (Z93) followed by irrigation after 80% of the soil moisture depletion; and (I4) water deficit stress from the start of the milking stage (Z77) to the ripening stage (Z93) followed by irrigation after 80% of the soil moisture depletion. The 3 cultivars of C1 (Sirvan), C2 (Pishtaz), and C3 (Marv dasht) were treated using the allocated sub-plots. The results revealed that by increasing the drought stress intensities on the wheat cultivars, Grain Yield (GY), Relative Water Content (RWC), and Total Chlorophyll Content (TCC) were decreased except for Proline Content (PC). Sirvan cultivar subjected to the treatment of drought stress (I3) led to the highest reduction in RWC and TCC compared to the control treatment (I1). The results of this study indicated that the wheat cultivars of Islamabad Agricultural Research Center had higher GY (5129 kg.h-1), TCC (58 mg. g-1 fr.wt.), and RWC (92%) values than those of the Agricultural Research Center of Islamic Azad University, Kermanshah branch.

Effect of terminal drought on yield and some physiological traits of winter wheat

Terminal drought i.e. drought during grain-filling phase is the most devastating environmental stress to wheat production. In present study the effect of terminal drought on physiological traits and its influence on yield and yield components in two winter wheat varieties (Kuna and Karla) were investigated. Terminal drought stress was applied from the beginning of anthesis by installing mobile plastic roof above the crops. Leaf gas exchange parameters, chlorophyll content index (CCI), relative water content (RWC), and nitrogen (N) content were measured three times during grain-filling phase, at early milk maturity (EMM), late milk maturity (LMM), and at early wax maturity (EWM). Grain yield and 1000 grain weight were measured by harvesting of each plot at crop maturity. Terminal drought enhanced leaf senescence and caused reduction of RWC, CCI, net photosynthetic rate (A), stomatal conductance (gs), and transpiration rate (E) as well as, grain yield and all measured yield components. However, grain yield and grain weight per ear were less affected in Karla indicating enhanced tolerance to terminal drought compared to Kuna variety. Higher tolerance to terminal drought in Karla is based on stay-green strategy. Stay-green strategy in Karla was characterized by retention of CCI at early wax maturity, which contributed to higher E and lower intercellular CO2 concentration compared to Kuna under terminal drought. Stay-green strategy as trait that enhanced terminal drought tolerance in Karla should be used in breeding programs and utilized to ensure maximum economic yields under terminal drought conditions.

Effect of drought and salinity stresses on morphological and physiological characteristics of canola

Environmental stresses such as salinity and drought are the most important factors affecting yield reduction and crops productivity. In order to investigate the effects of drought and salinity stresses on morphological and physiological characteristics of canola, an experimental campaign was conducted as a split plot based on a randomized complete block design with three replications at greenhouse of Agriculture Research Center and Natural Resources of East Azarbaijan in 2014. Main plots were including drought stress at four levels (0, −4, −8 and −12 bar polyethylene glycol solution) and subplots including salinity stress at four levels of sodium chloride (0, 75, 150 and 225 mM). The results analysis of variance indicated that the interaction of drought and salinity stresses was significant on leaf area and relative water content of leaf. The most leaf area (383.03 cm−2) was obtained at non-stress treatments. The results showed that drought stress conditions led to significant reduction in relative water content in leaf. The highest proline (0.08 µm/g fresh weight) and soluble sugars (0.12 mg/g fresh weight) contents were observed at treatments of −12 bar polyethylene glycol. Also, the least proline (0.04 µm/g fresh weight) and soluble sugar (0.06 mg/g fresh weight) contents were achieved at treatments of drought non-stress.

Highlighting the effects of coumarin on adult plants of Arabidopsis thaliana (L.) Heynh. by an integrated -omic approach

In this study, the effects of the allelochemical coumarin through a metabolomic, proteomic and morpho-physiological approach in Arabidopsis adult plants (25days old) were investigated. Metabolomic analysis evidenced an increment of amino acids and a high accumulation of soluble sugars, after 6days of coumarin treatment. This effect was accompanied by a strong decrease on plant fresh and dry weights, as well as on total protein content. On the contrary, coumarin did not affect leaf number but caused a reduction in leaf area. An alteration of water status was confirmed by a reduction of relative water content and an increase in leaf osmotic potential. Moreover, coumarin impaired plant bio-membranes through an increase of lipid peroxidation and H2O2 content suggesting that coumarin treatment might induce oxidative stress. Coumarin reduced the effective quantum yield of the photosystem II, the energy dissipation in the form of heat, the maximum PSII efficiency, the coefficient of the photochemical quenching and the estimated electron transport rate, while it significantly stimulated the fluorescence emission and the coefficient of the non photochemical quenching. Finally, the proteomic characterization of coumarin-treated plants revealed a down-regulation of the ROS detoxifying proteins, responsible of oxidative damage and consequently of physiological cascade effects.