Drought-sensitive Variety Research Articles

Genome-Wide Identification of Key Candidate microRNAs and Target Genes Associated with Peanut Drought Tolerance.

Peanut is an important crash crop worldwide, and it is often threatened by drought stress due to unexpected extreme weather events. In this work, NH5 and FH18 were selected as drought-tolerant and drought-sensitive varieties, respectively. Comparison of their physiological responses revealed that NH5 showed less wilting, higher relative water content and lower water loss rate of detached leaves, lower electrolyte leakage, and stronger antioxidant ability under drought stress than did FH18. Based on comparative transcriptomic analysis, 5376 differentially expressed mRNAs were commonly identified in the two varieties, and 2993 genes specifically changed in the drought-tolerant variety and were mainly enriched in photosynthesis-antenna proteins and photosynthetic pathways. Furthermore, 73 microRNAs (miRNAs) were differentially expressed in the drought tolerance variety specifically under drought stress; of these, two key candidate miRNAs, novel miR_416 and novel miR_73, were identified, and the majority of their target genes were enriched in phenylpropanoid biosynthesis, linoleic acid metabolism, and cutin, suberine, and wax biosynthesis. This study lays the foundation for the analysis of the molecular mechanism of drought tolerance and promotes the genetic improvement of peanut drought tolerance.

Oxidative stress and antioxidant metabolites in wheat (Triticum aestivum L.) varieties during grain development under water deficit conditions

Two wheat (Triticum aestivum L.) varieties viz. WH 1105 and WH 1025 are subjected to drought stress. The non enzymatic antioxidant defense system which contains antioxidant metabolites such as ascorbic acid, glutathione and carotenoids contents were studied in drought sensitive and drought resistant varieties days after anthesis (DAA) in leaf and grain samples. As part of protective mechanism against drought, wheat plants produced more of ascorbic acid and glutathione with a concomitant decrease in carotenoid content. The increase in ascorbic acid and glutathione were more in WH 1025 than WH 1105. Carotenoids protect plants by minimizing ROS formation by quenching oxygen. The reduction in carotenoid content was observed in both wheat varieties days after anthesis (DAA) in leaf and grain samples but more reduction was observed in WH 1105 which is a drought sensitive variety of wheat. These antioxidant metabolites played a key role in protecting wheat plants against reactive oxygen species (ROS) mediated oxidative damage and their redox buffering capacity generates stress tolerance in drought tolerant wheat variety WH 1025.

Kuraklık Stresi Altındaki Buğday Çeşitlerinde Salisilik Asit Uygulamalarının miRNA İfadesi Üzerine Etkileri

Wheat cultivation in Turkey; is highly affected by environmental factors, such as drought stress, which reduces yields significantly. Applying chemicals that stimulate plant growth is an easy, low-cost, low-risk and effective approach to increase stress tolerance, and salicylic acid is prominent in adapting plants to adverse environmental conditions such as drought stress, salinity, and improving plants' tolerance to stress. In the study, Gün91 was used as drought tolerant variety and Ankara98 was used as the sensitive variety and two different doses (0.1 mM, 0.5mM) of salicylic acid were applied to the plants. Drought stress application was performed one week after salicylic acid application and RNAs were isolated from leaf samples collected from application and control pots, and expression levels of miR156, miR169, miR172, miR319 and mir398 and target genes belonging to these miRNAs were determined. While the expression level of miR156 and miR172 was higher in Day91 with tolerance to drought stress in leaf tissues treated with salicylic acid under drought stress conditions; the level of miR169 was higher in the sensitive Ankara98 variety. In Gün91 variety, miR319 expression level was higher in 0.5 mM salicylic acid + drought application, whereas in Ankara98 variety was higher in 0.1 mM salicylic acid + drought application. The miR398 expression level showed a significant decrease in both Gün91 and Ankara98 varieties in the plant groups where salicylic acid and drought stress were applied together compared to the control group. As a result; with this study, it was emphasized that salicylic acid is an important signal molecule in response to stress and it mitigates the effect in stress conditions, and the tolerance mechanism of drought tolerant and sensitive varieties with salicylic acid application were different.

Lipid Peroxidation and Chlorophyll Fluorescence of Photosystem II Performance during Drought and Heat Stress is Associated with the Antioxidant Capacities of C3 Sunflower and C4 Maize Varieties.

Agricultural production is predicted to be adversely affected by an increase in drought and heatwaves. Drought and heat damage cellular membranes, such as the thylakoid membranes where photosystem II occurs (PSII). We investigated the chlorophyll fluorescence (ChlF) of PSII, photosynthetic pigments, membrane damage, and the activity of protective antioxidants in drought-tolerant and -sensitive varieties of C3 sunflower and C4 maize grown at 20/25 and 30/35 °C. Drought-tolerant varieties retained PSII electron transport at lower levels of water availability at both temperatures. Drought and heat stress, in combination and isolation, had a more pronounced effect on the ChlF of the C3 species. For phenotyping, the maximum fluorescence was the most effective ChlF measure in characterizing varietal variation in the response of both species to drought and heat. The drought-tolerant sunflower and maize showed lower lipid peroxidation under drought and heat stress. The greater retention of PSII function in the drought-tolerant sunflower and maize at higher temperatures was associated with an increase in the activities of antioxidants (glutathione reductase, superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase), whereas antioxidant activity declined in the drought-sensitive varieties. Antioxidant activity should play a key role in the development of drought- and heat-tolerant crops for future food security.

RNA-seq Reveals Differentially Expressed Genes between Two indica Inbred Rice Genotypes Associated with Drought-Yield QTLs

Two indica inbred rice lines, IR64, a drought-sensitive, and Apo, a moderately drought-tolerant genotype, were exposed to non- (control or unstressed) and water-stress treatments. Leaf samples collected at an early flowering stage were sequenced by RNA-seq. Reads generated were analyzed for differential expression (DE) implementing various models in baySeq to capture differences in genome-wide transcriptional response under contrasting water regimes. IR64, the drought-sensitive variety consistently exhibited a broader transcriptional response while Apo showed relatively modest transcriptional changes under water-stress conditions across all models implemented. Gene ontology (GO) and KEGG pathway analyses of genes revealed that IR64 showed enhancement of functions associated with signal transduction, protein binding and receptor activity. Apo uniquely showed significant enrichment of genes associated with an oxygen binding function and peroxisome pathway. In general, IR64 exhibited more extensive molecular re-programming, presumably, a highly energy-demanding route to deal with the abiotic stress. Several of these differentially expressed genes (DEGs) were found to co-localize with QTL marker regions previously identified to be associated with drought-yield response, thus, are the most promising candidate genes for further studies.

Wilting index and root morphological characteristics used as drought-tolerance variety selection at the seedling stage in soybean (Glycine max L.)

Drought stress is a common issue that affects agriculture production. The soybean plant is one of the drought-sensitive crops that could lose the yield of up to 40% under severe drought years. Improvements in drought tolerance have been one of the main objectives of breeding programs in soybean. In this study, 62 soybeans [Glycine max (L.) Merri.] germplasms including landraces and elite cultivars were evaluated by analyzing canopy and root morphological characteristics at seedling stage under polyethylene glycol (2.5 M PEG 8000, − 0.54 MPa) simulated drought stress. The results showed that the wilting index of sixty-two soybean germplasms showed significant polymorphism differences after 4 days PEG treatment. The lowest wilting index was 2.75 in Tiefeng 31, while the largest reached 9 in Fengdou 93 and Songzidou. The wilting index was positively correlated with plant height, electrolyte leakage, and negatively correlated with a dry weight of the above-ground part, stomatal conductance, and transpiration rate by regression analysis. The root system architecture (RSA) study showed root-canopy ratio, root length, number of the lateral roots, root surface area, and root volume were significantly negatively correlated with the wilting index and positively correlated with the root volume. Based on these results, sixty-two soybean germplasms were comprehensively evaluated for drought-tolerant cultivar by the principal component analysis (PCA). The results showed that Tiefeng 31 was the most drought-tolerant elite cultivar. However, Fengdou 93 was the most drought-sensitive elite variety. The drought tolerance screening results were consistent with the wilting index and RSA analysis, especially the root length. Both droughts tolerant and sensitive elite cultivar could be further used to breed drought-tolerant germplasms and to clarify the drought tolerance mechanism in soybean.

Proline and carbohydrate metabolism in rice varieties (Oryza sativa L.) under various drought and recovery conditions

Drought stress is a main limitation of rice production in many regions worldwide, as most improved rice varieties are not drought tolerant. This study analyzed the effects of various drought stresses and subsequent recovery on dry weight accumulation and biochemical characteristics of different rice varieties (the drought-tolerant variety DA8, the drought-sensitive variety Malagkit Pirurutong, and the fast-recovering variety Kinandang Patong). The water treatments were irrigated (control), drought stress, and subsequent re-watering. The results showed that under the same drought stress level, DA8 retained higher water content than the other varieties. In addition, water content in sheaths was higher than that in leaves. DA8 obtained a higher dry weight accumulation than the other varieties under both the control and drought conditions. Proline content in all varieties increased significantly after drought stress. In addition, it accumulated more in leaves than in sheaths. DA8 expressed a higher ability to accumulate proline than Malagkit Pirurutong or Kinandang Patong. Total soluble sugar and starch contents of the three varieties decreased under drought stress compared to control. However, the change in total soluble sugar and starch levels depended not only on the drought stress condition but also on the environment and variety. Proline-accumulating ability under drought stress may be a useful indicator of the drought tolerance of rice.

Morphological, transcriptomic and proteomic responses of contrasting rice genotypes towards drought stress

Rice is a global staple crop that has a large requirement of water at various growth and developmental stages. As a matter of fact, drought can substantially reduce rice yield. The traits responsible for drought tolerance can be selected and studied to improve rice growth and yield under stress conditions.In the present study, morphological, physiological, biochemical and molecular variations between drought tolerant (PB6 and Moroberakan) and drought sensitive (Way Rarem) varieties have been evaluated. Notable differences have been observed in root morphology, root xylem number and area, stomata number, relative water content, proline content, protein and gene expression. In addition, novel automated frameworks based on computer vision algorithms have been employed for high-throughput quantification of xylem using scanning electron microscopy images.Transcriptome analysis has revealed variation in expression of Med37c and RSOsPR10 genes among various rice varieties. The differential proteome analysis using 2-D followed by MALDI-based identification implied the role of chitinases in drought tolerance. The information generated from computational/digital image analysis as well as biochemical studies can contribute significantly towards the developing field of rice phenomics.

Field performance of bacterial inoculants to alleviate water stress effects in wheat (Triticum aestivum L.)

Plant growth promoting bacteria (PGPB) containing 1-aminocyclopropane-1-carboxylate (ACC) deaminase can play an important role in abiotic stress tolerance in plants, particularly drought. The objective of this study was to evaluate bacterial strains Variovorax paradoxus RAA3, Pseudomonas palleroniana DPB16, Pseudomonas sp. UW4 for their ability to alleviate drought stress in wheat in field experiments under irrigated and rain-fed conditions in the Uttarkhand region of India. In this study, ACC deaminase producing bacterial strains Pseudomonas palleroniana DPB16, Pseudomonas sp. UW4 and Variovorax paradoxus RAA3 were evaluated for their efficiency in improving growth, nutrient content and yield of wheat varieties, HD2967 (drought sensitive) and PBW660 (drought tolerant) under rainfed (drought) and irrigated conditions. Bacterial inoculants increased grain and straw yields at both sites, however the response to inoculation was considerably higher under rainfed conditions (64 to 90% increase with inoculation) compared to that observed under irrigated conditions (22 to 40% increase with inoculation). Of the three seed-coated inoculants tested, strain RAA3 maximally improved grain yield (28.2%, 47.4%), straw yield (11.2%, 26.0%) and harvest index (10.6%, 15.3%) under irrigated and rainfed conditions, respectively, compared to non-inoculated crops. The relative expression of the drought responsive gene aquaporin (TaTIP1;1), in response to inoculation, was significantly higher (3.34-fold) in the wheat variety PBW 660, as compared to the drought sensitive variety HD 2967 in which the expression level of aquaporin was unaffected. Under rainfed conditions, the relative mRNA level of the helicase gene WDH45 was significantly higher in HD 2967 (1.54-fold) than the PBW 660 (3.69-fold). Bacterial inoculation caused significant positive changes in plant biochemical and antioxidant properties compared to uninoculated plants. Overall, the results show that the selected PGPB containing ACC deaminase activity along with other plant growth promoting characteristics are effective inoculants for improving wheat yields in irrigated and rainfed field experiments.

A novel ABA functional analogue B2 enhances drought tolerance in wheat

Drought stress negatively affects wheat growth and yield. Application of drought agent is an effective way to improve crop drought tolerance, therefore increasing crop yield. Based on the structure of abscisic acid (ABA), Pyrabactin and coronatine (COR), we designed the target compound B2. To investigate the function of B2 in alleviating drought stress on wheat, the drought-resistant variety ND212 and drought-sensitive variety LX99 were used under hydroponic conditions. The results showed that B2 had a similar function with ABA, especially 0.01 μmol·L−1 B2. Under drought stress conditions, 0.01 μmol·L−1 B2 increased the water content of wheat, enhanced the osmotic adjustment ability of leaves, and reduced the toxicity of reactive oxygen species on cells. What’s more, 0.01 μmol·L−1 B2 improved the expression level of ABA-responsive genes TaSnRK2.4 and TaMYB3R1. It also improved the expression level of drought-responsive genes TaSRHP and TaERF3. Taken together, B2 enhanced drought tolerance in wheat by activating ABA signaling pathway.

Different growing strategies of two winter wheat cultivars under rainfed conditions during dry years in North China Plain

The North China Plain (NCP) is a severe water shortage region, especially during the wheat growing season. Understanding the response of grain yield and water availability in winter wheat cultivars (Triticum aestivum L.) is important to adjust planting structure under groundwater reducible exploitation in rainfed dry years of NCP. Field experiments were conducted at the Luancheng Agroecosystem Experiment Station of the Chinese Academy of Sciences, Hebei, China. Two different drought resistant winter wheat cultivars (Jinmai47 and Shiluan02-1) were grown under rainfed conditions during four years of 2010-2011, 2011-2012, 2012-2013 and 2013-2014. Grain yield and its components, aboveground biomass (AB), dry matter accumulation translocation efficiency, water consumption, water use efficiency at field scale, and photosynthetic characteristics were measured. The results showed that Jinmai47 rapidly accumulated AB by higher tiller and photosynthetic potential comparing with those of Shiluan02-1. Its grain yield was 16.49% higher than that of the drought-sensitive winter wheat variety Shiluan02-1 during the four rainfed years. However, the dry matter remobilization efficiency (DMRE) and contribution of dry matter remobilization from heading stage to maturity stage to grain (CDMRE) of Shiluan02-1 was higher than those of Jinmai47. The average water use efficiency at grain yield level (WUEy), WUE at aboveground biomass level (WUEab), and WUE at grain yield under rainy conditions (WUEr) of Jinmai47 were 11.08%, 16.41%, and 17.21% higher than those of Shiluan02-1. There was a significant difference in the WUEab and WUEr between the two wheat cultivars. The two wheat varieties under drought condition have different growing strategies. Jinmai47 has more tiller number, earlier vigor, and higher AB than Shiluan02-1, helping it to adapt to the fluctuations in the environment. Keywords: winter wheat cultivar, grain yield, rainy treatment, water use efficiency, dry year DOI: 10.25165/j.ijabe.20181105.4344 Citation: Dong B D, Yang H, Qiao Y Z, Zhang M M, Wang Y K, Jin L L, et al. Different growing strategies of two winter wheat cultivars under rainfed conditions during dry years in North China Plain. Int J Agric & Biol Eng, 2018; 11(5): 150–159.

Effects of different types of polyamine on growth, physiological and biochemical nature of lettuce under drought stress

This study explored the effects of drought stress on scattered leaf lettuce seedlings and the effects of different types of polyamines (PAs) on the morphological indexes and antioxidant enzyme activities of scattered leaf lettuce. The drought-sensitive variety “Victoria crispy” was used as the plant material, and 10% Polyethylene Glycol (PEG) 6000 was used to simulate drought stress. Foliar applications of 0.1 millimoles per litre of three polyamines [putrescine (Put), spermidine (Spd) and spermine (Spm)] were performed at the seedling stage (the control group was sprayed with water). The morphological indices and antioxidant enzyme activity were recorded on the eighth day after treatment. The results showed that drought stress significantly decreased the morphological indices of scattered leaf lettuce, and spraying different types of PAs had a mitigating effect. Drought stress significantly reduced the ascorbic acid peroxidase (APX), catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD) activity, increased the content of malondialdehyde (MDA), and exogenous polyamine spraying significantly affected the antioxidant enzyme activity. Among the polyamines, Put showed the most noticeable effect of mitigation. Drought stress had a significant effect on the morphological and antioxidant enzyme activities of scattered leaves lettuce, and Put was the most effective PA to increase drought tolerance.

Assessing the correlation of genotypic and phenotypic responses of indica rice varieties under drought stress

Drought is one of the severe abiotic stress that affects the productivity of rice, an important staple crop that is consumed all over the world. The traits responsible for enhancing or adapting drought resistance in rice plants can be selected and studied to improve their growth under stress conditions.Experiments have been conducted on indica rice varieties comprising Sahabhagidhan as drought tolerant variety and IR64, MTU1010 categorized as drought sensitive varieties. Various root related biochemical and morphological traits such as root length, relative water content (RWC), xylem number, xylem area, proline content, and malondialdehyde content have been investigated for a comparative study of the plant response to drought stress in different rice varieties.The results of differential root transcriptome analysis have revealed that there is a notable difference in gene expression of OsPIP2;5 and OsNIP2;1 in various indica varieties of rice at different time periods of stress. The present work aims at assessing the correlation between genotypic and phenotypic traits that can contribute towards the emerging field of rice phenomics.

Physiological and biochemical mechanism of spermidine improving drought resistance in maize seedlings under drought stress.

To explore the role of exogenous spermidine (Spd) in enhancing the resistance of maize to drought stress, 15% polyethylene glycol (PEG-6000) was used to simulate drought stress and with 'Xianyu 335' (drought-insensitive) and 'Fenghe 1' (drought sensitive) as the experiment materials, the effects of Spd (0.1 mmol·L-1) on the growth, photosynthetic characteristics, chlorophyll content, osmotic adjustment substance, membrane lipid peroxidation and root activity of maize seedlings were investigated. The results showed that the application of Spd significantly promoted the growth of maize seedlings under drought stress, increased chlorophyll content, net photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (Tr) and water use efficiency (WUE), and decreased the enhancement of intercellular carbon dioxide concentration (Ci) in 'Fenghe 1'. Moreover, the stomatal and non-stomatal limitations of photosynthetic ability caused by drought stress in 'Fenghe 1' were effectively reduced by exogenous Spd. The application of Spd increased the content of proline and soluble sugar, decreased theO2-· generation rate, contents of H2O2 and MDA and cell membrane permeability, enhanced the root activity. The changes of drought-sensitive 'Fenghe 1' were greater than drought-tolerant 'Xianyu 335'. These results indicated that exogenous Spd had positive effects on the seedlings to capture and converse solar energy, thus promoting photosynthesis and the growth of maize seedlings. It would also enhance the adaptability of seedlings to drought stress by reducing the production of reactive oxygen species (ROS), increasing the accumulation of osmotic adjustment substances to stabilize the cell membrane system and improving the root vigor. The positive effects of Spd was more obvious for drought-sensitive variety 'Fenghe 1'.

Evaluation of genetic diversity in drought tolerant and sensitive varieties of wheat using ISSR markers

Drought stress is one of the major constraints that greatly limit the productivity of wheat worldwide. Deciphering the molecular basis of drought tolerance can help in combating drought stress. Therefore, the present study was undertaken to determine genetic diversity among six drought tolerant and six drought sensitive varieties of wheat. Out of 15 ISSR primers used, 14 primers gave reproducible banding pattern. These 14 primers generated 191 amplified products out of which 93 were polymorphic. Overall size of PCR amplified products ranged between 400 bp and 4000 bp. Based on similarity matrix data, the value of similarity coefficient ranged from 0.70 to 0.94. Cluster analysis discriminated the wheat varieties into two major clusters, one consisted of drought tolerant varieties and the other had all drought sensitive varieties. The present study showed that ISSR markers provide a valuable tool to study genetic variability in wheat varieties.

Rooting traits of peanut genotypes differing in drought tolerance under drought stress

The effects of two water regimes (well-watered condition or drought stress) on root length,root surface area and root volume were tested on two peanut genotypes (the drought-resistantvariety HuaYu 22 (HY22) and the drought-sensitive variety HuaYu 23 (HY23)), measured 101days after sowing. The roots were sampled from the upper (0–40 cm) and deeper (40–100 cm)soil layers. Root diameter was measured to the nearest 0.5 mm in describing its distribution.Total dry weight and pod yield were measured at harvest. The drought tolerance index of podyield and the harvest index in HY22 were higher than those in HY23. The total root lengthdensity (RLD), total root surface area and volume were significantly higher for HY22 thanHY23. The RLD in the deeper soil layer was lower for HY23 than HY22. Under drought stress,the percent RLD in the deeper layers increased in both genotypes. Compared to well-wateredcondition, the total root surface area and root volume in the upper soil layer were lower underdrought stress and root traits in deeper soil layers were higher. Drought stress had no impact onvery fine roots (diameter < 0.5 mm) of HY22 in the deeper soil layer but lowered their share inHY23 markedly. The RLD and root surface area in the deeper soil layer were related to the podyield of peanut. This finding could be useful in growing peanut under drought conditions.

Drought priming improves subsequent more severe drought in a drought-sensitive cultivar of olive cv. Chétoui

Drought is a major factor limiting crop production worldwide. The objective of this study was to test whether pre-exposure to drought can enhance the subsequent drought response of a drought–sensitive variety of olive cv. Chétoui.Seven-months old olive plants were grown in a controlled conditions and divided into control plants (irrigated daily), primed plants (PP, primed by exposure to drought for 21days, re-watered for 60days and then exposed to water depletion for 30days) and non-primed plants (NPP, well watered for 81days and immediately followed by intermediate drought as PP). Compared to the non-primed plants, primed plants showed an improvement in biomass production and healthy values of photosynthesis parameters with a higher accumulation of photosynthetic pigments. Additionally, the data of chlorophyll fluorescence were significantly similar to those of control, implying that no photodamage was occurred. Moreover, primed plants exhibited high accumulation of total sugar and proline which lead to the better water status maintenance. The lower level of oxidative status measured in term of hydrogen peroxide (H2O2), malondiadehyde (MDA) and electrolyte leakage (EC) in primed plants confirmed the alleviation of oxidative stress. Furthermore, the primed plants possessed more effective oxygen scavenging systems as exemplified by the increased activities of CAT, SOD, GP and high accumulation of polyphenols, resulting in a better maintenance in homeostasis of ROS production. Our investigation is indicative of the result of the benefit memory effects caused by stress pre-exposure in young olive plants cv.’Chétoui’ to overcome subsequent stress.

Drought-tolerant QTL qVDT11 leads to stable tiller formation under drought stress conditions in rice

Drought is an important limiting factor for rice production, but the genetic mechanisms of drought tolerance is poorly understood. Here, we screened 218 rice varieties to identify 32 drought-tolerant varieties. The variety Samgang exhibited strong drought tolerance and stable yield in rain-fed conditions and was selected for further study. To identify QTLs for drought tolerance, we examined visual drought tolerance (VDT) and relative water content (RWC) phenotypes in a doubled haploid (DH) population of 101 individuals derived from a cross between Samgang and Nagdong (a drought-sensitive variety). Three QTLs from Samgang were identified for VDT and explained 41.8% of the phenotypic variance. In particular, qVDT11 contributed 20.3% of the phenotypic variance for RWC. To determine QTL effects on drought tolerance in rain-fed paddy conditions, seven DH lines were selected according to the number of QTLs they contained. Of the drought-tolerance-associated QTLs, qVDT2 and qVDT6 did not affect tiller formation, but qVDT11 increased tiller number. Tiller formation was most stable when qVDT2 and qVDT11 were combined. DH lines with both of these drought-tolerance-associated QTLs exhibited the most stable tiller formation. Together, these results suggest that qVDT11 is important for drought tolerance and stable tiller formation in rain-fed paddy fields.

Adaptation to high temperature mitigates the impact of water deficit during combined heat and drought stress in C3 sunflower and C4 maize varieties with contrasting drought tolerance.

Heat and drought stress frequently occur together, however, their impact on plant growth and photosynthesis (PN ) is unclear. The frequency, duration and severity of heat and drought stress events are predicted to increase in the future, having severe implications for agricultural productivity and food security. To assess the impact on plant gas exchange, physiology and morphology we grew drought tolerant and sensitive varieties of C3 sunflower (Helianthus annuus) and C4 maize (Zea mays) under conditions of elevated temperature for 4 weeks prior to the imposition of water deficit. The negative impact of temperature on PN was most apparent in sunflower. The drought tolerant sunflower retained ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) activity under heat stress to a greater extent than its drought sensitive counterpart. Maize exhibited no varietal difference in response to increased temperature. In contrast to previous studies, where a sudden rise in temperature induced an increase in stomatal conductance (Gs ), we observed no change or a reduction in Gs with elevated temperature, which alongside lower leaf area mitigated the impact of drought at the higher temperature. The drought tolerant sunflower and maize varieties exhibited greater investment in root-systems, allowing greater uptake of the available soil water. Elevated temperatures associated with heat-waves will have profound negative impacts on crop growth in both sunflower and maize, but the deleterious effect on PN was less apparent in the drought tolerant sunflower and both maize varieties. As C4 plants generally exhibit water use efficiency (WUE) and resistance to heat stress, selection on the basis of tolerance to heat and drought stress would be more beneficial to the yields of C3 crops cultivated in drought prone semi-arid regions.

Drought-induced changes in photosynthetic apparatus and antioxidant components of wheat (Triticum durum Desf.) varieties

Water deficit is a key factor influencing the yield and quality of crops. In the present study, the photosynthetic responses by means of chlorophyll fluorescence of chloroplasts, thylakoid membrane proteins, and antioxidant components were analyzed in wheat (Triticum durum Desf.) plants differing in their tolerance to drought. Two durum winter wheat varieties, Barakatli 95 (drought tolerant) and Garagylchyg 2 (drought sensitive) were grown under field well-watered and drought conditions. It was found that contents of the PS I core (CPI) with Mr of 123 kD and apoprotein P700 with Mr of 63 kD were relatively higher in Barakatli 95 variety under drought stress compared with the control plants. Synthesis of α- and β-subunits of CF1 ATP-synthase complex with Mr of 55 and 53.5 kD also slightly increased in the tolerant Barakatli 95 and decreased in the drought sensitive variety Garagylchyg 2. A decrease in the intensity of 30 kD band and a significant increase were found in the content of the 25-16 kD region in Garagylchyg 2 variety. The synthesis of 60 kD and content of low molecular mass polypeptides (21.5 and 12 kD) were increased in the tolerant genotype Barakatli 95. The intensity of peaks at 687, 695, and 742nm considerably increases in the fluorescence spectra (77K) of chloroplasts isolated from the sensitive variety Garagylchyg 2, and there is a stimulation of the ratio of fluorescence band intensity F687/F740. At the same time, higher level of glycine betaine was found in the drought tolerant variety compared with the control one throughout the different periods of growth.