Superoxide dismutase and peroxidase activities in drought sensitive and resistant barley (Hordeum vulgare L.) varieties

The effects of water deficit on relative water content (RWC), on the activity superoxide dismutase (SOD) and peroxidase (POX) from leaves of two drought-resistant barley strains (Hordeum vulgare L.) varieties (TOKAK-157/37 and 56000/MISC-233) and one sensitive (ERGINEL-90) were studied. In 21 day old seedlings, drought stress was initiated by withholding water and lasted for 12 days. Activity of SOD increased by the effect of drought treatments in the leaves of drought-resistant varieties TOKAK-157/37 and 56000/MISC-233 as compared to sensitive variety ERGINEL-90. The drought treatment resulted in a 418 % and 59 % increase in SOD activity in resistant varieties at the end of the 12^th day of experimental period. However, an increase in activity of SOD was not accompanied by an increase in activity of POX in drought-resistant TOKAK-157/37 and 56000/MISC-233 except on the 6^th day of drought treatment in 56000/MISC-233. In drought-sensitive variety, ERGINEL-90, POX activity did not change throughout drought period.     

Effect of ploidy levels on the activities of Δ1-pyrroline-5-carboxylate synthetase,superoxide dismutase and peroxidase in Cenchrus species grown under water stress

The effects of ploidy levels on the activities of Δ¹-pyrroline-5-carboxylate synthetase (P5CS; EC not assigned), superoxide dismutase (SOD; EC 1.15.1.1) and guaiacol peroxidase (POX; EC 1.11.1.7), as well as malondialdehyde (MDA) and proline contents were studied in two months old plants of Cenchrus species. The Cenchrus species represent three ploidy levels: diploid, tetraploid, hexaploid and two life spans: annual and perennial. Plants were subjected to water stress for 2, 4, 6 and 8 d by withholding water under glasshouse conditions. Although the levels of proline increased with the magnitude of water stress, the P5CS activity did not show a corresponding increase in all species. Peroxidase and superoxide dismutase activities showed an increase or steady state in the early phase of drought and then declined with the further increase in the magnitude of water stress, indicating differing behaviors of species towards drought tolerance. Under drought, diploid Cenchrus species had a higher POX activity, MDA accumulation and lower proline content than tetraploid species. Lower POX and higher P5CS activities and proline contents, however, were observed in hexaploid and tetraploid species. Taken together, our findings suggest that diploid species have a less efficient antioxidant system to scavenge reactive oxygen species than tetra and hexaploid Cenchrus. This may result in a corresponding variability in growth and persistence under natural grasslands. The study also paves the way for investigations on the molecular events associated with drought in Cenchrus species differing in ploidy and life span.     

Water deficit and aluminum tolerance are associated with a high antioxidative enzyme capacity in Indica rice seedlings

Plant growth and productivity are greatly affected due to changes in the environmental conditions. In the present investigation, the interactive effects of two important abiotic stresses, i.e., water deficit and Al toxicity, were examined in the seedlings of two rice (Oryza sativa L.) cvs. Malviya-36 (water deficit/Al sensitive) and Vandana (water deficit/Al tolerant). When 15 days grown seedlings were exposed to water deficit (created with 15 % polyethylene glycol 6000) or Al (1 mM AlCl₃) treatment or both the treatments together for 48 h, the lengths of root/shoot, relative water content, and chlorophyll greatly declined in the seedlings of the sensitive cultivar, whereas in the tolerant seedlings, either little or insignificant decline in these parameters was observed due to the treatments. Seedlings subjected to water deficit or Al treatment alone or in combination showed increased intensity of the isoenzyme activity bands of superoxide dismutase (SOD), guaiacol peroxidase (GPX), and ascorbate peroxidase (APX) in in-gel activity staining studies. Water deficit caused decrease in intensity of catalase (CAT) activity bands; however, when seedlings were exposed to AlCl₃ alone or in combination with water deficit, the intensity of the CAT isoforms increased in both the rice cultivars. The level of expression of the activity bands of SOD, CAT, GPX, and APX was always higher in the seedlings of tolerant cv. Vandana compared to the sensitive cv. Malviya-36 under both controls as well as stress treatments. Higher intensity of isozymes representing higher activity levels of antioxidative enzymes in the rice seedlings and their further increase under water deficit, Al exposure, or in combination of both the stresses appears to serve as useful marker for specifying a combination of water deficit and Al tolerance in rice.     

Physiochemical and antioxidant responses of the perennial xerophyte Capparis ovata Desf. to drought

Caper (Capparis ovata Desf.) is a perennial shrub (xerophyte) and drought resistant plant which is well adapted to Mediterranean Ecosystem. In the present study we investigated the plant growth, relative water content (RWC), chlorophyll fluorescence (F_V/F_M), lipid peroxidation (TBA-reactive substances content) as parameters indicative of oxidative stress and antioxidant enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase (POX), catalase (CAT) and glutathione reductase (GR) in relation to the tolerance to polyethylene glycol mediated drought stress in C. ovata seedlings. For induction of drought stress, the 35 days seedlings were subjected to PEG 6000 of osmotic potential −0.81 MPa for 14 days. Lipid peroxidation increased in PEG stressed seedlings as compared to non-stressed seedlings of C. ovata during the experimental period. With regard to vegetative growth, PEG treatment caused decrease in shoot fresh and dry weights, RWC and F_V/F_M but decline was more prominent on day 14 of PEG treatment. Total activity of antioxidative enzymes SOD, APX, POX, CAT and GR were investigated in C. ovata seedlings under PEG mediated drought. Induced activities of SOD, CAT and POX enzymes were high and the rate of increment was higher in stressed seedling. APX activity increased on both days of PEG treatment, however, increase in GR activity was highest on day 14 of drought stress. We concluded that increased drought tolerance of C. ovata is correlated with diminishing oxidative injury by functioning of antioxidant system at higher rates under drought stress.     

The effects of boron toxicity on root antioxidant systems of two chickpea (Cicer arietinum L.) cultivars

Significant differences in the antioxidant systems of the roots of two chickpea (Cicer arietinum L.) cultivars differing in tolerance to drought were observed in under toxic boron (B) conditions. Three-week-old chickpea seedlings were subjected to 0.05 mM (control), 1.6 mM or 6.4 mM B in the form of boric acid (H₃BO₃) for 7 days. At the end of the treatment period, root length, dry weight, boron concentration, malondialdehyde (MDA) content, and the activities of antioxidant enzymes—superoxide dismutase (SOD), peroxidase (POX), catalase (CAT), ascorbate peroxidase (APOX) and glutathione reductase (GR)—were measured. Root length of the drought-tolerant Gökce cultivar did not change under 1.6 mM B but increased under 6.4 mM B. On the contrary, root length decreased in the drought-sensitive Küsmen cultivar under both B concentrations. While root dry weight was unaffected in Gökce, it decreased in Küsmen under both B concentrations. Boron concentration was significantly higher in Küsmen than in Gökce at both B levels. Significant increases in SOD and POX activities were observed in roots of both cultivars under 1.6 and 6.4 mM B. Root extracts exhibited three SOD and three POX activity bands in both cultivars under B stress when compared to control groups. Although CAT activity in Gökce was increased, it decreased in Küsmen at the highest B concentration as compared to control groups. Roots of both cultivars showed no significant change in APOX activity under B toxicity (except in 1.6 mM B treated roots of Küsmen) when compared to control groups. GR activity in the roots of Küsmen decreased significantly with increasing B concentration. However, a significant increase in GR activity was found in Gökce under 1.6 mM B stress. In addition, lipid peroxidation levels of drought-sensitive Küsmen increased, indicating more damage to membrane lipids due to B toxicity. Lipid peroxidation did not change in the drought-tolerant Gökce cultivar at either B concentration. These results suggest that roots of Gökce are better protected from B-stress-induced oxidative stress due to enhanced SOD, CAT and POX activities under high B levels.     

Effects of progressive drought stress on the physiology,antioxidative enzymes and secondary metabolites of Radix Astragali

The dried roots of Radix Astragali are widely used in traditional Chinese medicine, and flavonoids present in the root of this herb have been implicated in its bioactivity. We subjected 2-year-old Astragalus membranaceus Bge. var. mongholicus (Bge.) Hsiao to a progressive drought stress over 14 days of water withholding and studied the physiological and biochemical responses and secondary metabolite accumulation. Results indicated that drought stress reduced relative water content, reduced yield, but increased electrolyte leakage, malondialdehyde, proline and soluble sugar content. Mild and moderate drought stress enhanced some antioxidative enzyme activity to protect plants from damaging, but antioxidative enzyme activity was limited by severe stress. The calycosin-7-O-β-d-glycoside and ononin content of plant roots was enhanced with degree of drought stress, whereas calycosin and formononetin levels did not differ significantly until 14 days. These results demonstrate that Radix Astragali can adapt to water stress by up-regulating antioxidant enzymes and accumulation of osmotic agents, and a certain degree of drought stress can enhance accumulation of some flavonoids, potentially facilitating higher yields of pharmacological activity of calycosin-7-O-β-d-glycoside production.     

Root desiccation and drought stress responses of bareroot Quercus rubra seedlings treated with a hydrophilic polymer root dip

Root hydrogel, a hydrophilic polymer, has been used to improve transplanting success of bareroot conifer seedlings through effects on water holding capacity. We examined mechanisms by which Terra-sorb® Fine Hydrogel reduces damage that occurs when roots of 1-year old, dormant northern red oak (Quercus rubra L.) were subjected to short-term (1, 3, and 5 h) pre-transplanting desiccation and long-term (45 days) drought stress following transplanting in a controlled environment chamber or greenhouse conditions. Hydrogel-treated seedlings had 80% greater root moisture content than non-root dipped control seedlings following the pre-transplanting desiccation period. Hydrogel reduced root membrane leakiness by 31% 5 h after the desiccation exposure. Hydrogel-treated seedlings did not show greater differences in shoot length, plant dry mass, root volume, net photosynthesis, and stomatal conductance compared with control seedlings following the 45-day drought stress exposure. A reduction in mean number of days to bud break in hydrogel-treated seedlings, combined with delayed tissue moisture loss (linked to higher stem water potential), suggests that hydrogel may have provided stress protection to aid survival under short-term desiccation, which may be beneficial toward alleviating initial transplanting stress.     

Oxidative stress, protein carbonylation, proteolysis and antioxidative defense system as a model for depicting water deficit tolerance in Indica rice seedlings

Water deficit is an important constraint to rice (Oryza sativa L.) productivity. The present study was undertaken to investigate whether the level of oxidative stress, carbonylation of proteins, proteolysis and status of antioxidative defense could serve as a model to distinguish water deficit tolerant and sensitive rice cultivars. When 10-day-grown seedlings of two rice cultivars, Malviya-36 (drought-sensitive) and Brown Gora (drought-tolerant) were subjected to ?1.0 and ?2.1 MPa water deficit treatments for 24–72 h with polyethylene glycol 6000 in the medium, a greater decline in the growth of the seedlings and levels of leaf water potential, relative water content, Chl a, Chl b, carotenoids and greater increase in leaf water loss were observed in the sensitive cultivar than the tolerant. Under similar level of water deficit seedlings of sensitive cultivar showed higher level of superoxide anion generation, H₂O₂, lipid peroxidation and proteolysis in roots as well as shoots compared to the tolerant. Drought-tolerant cultivar had higher constitutive level of antioxidative enzymes superoxide dismutase and catalase and the activities of these two enzymes alongwith of guaiacol peroxidase showed greater increase in this cultivar under water deficit compared to the sensitive. A significant decline in the level of protein thiol and a higher increase in protein carbonyls content, also confirmed by protein gel blot analysis with an antibody against 2,4-dinitrophenylhydrazine was observed in the seedlings of drought sensitive cv. Malviya-36 compared to the tolerant cv. Brown Gora when subjected to similar level of water deficit. Seedlings of drought sensitive cultivar, under water deficit, showed higher proteolytic activity, higher number of in-gel activity stained proteolytic bands and higher expression of oxidized proteins in roots compared to the tolerant cultivar. Results suggest that poor capacity of antioxidative enzymes could be, at least partly, correlated with water deficit sensitivity of sensitive cultivar and that higher activity of antioxidative enzymes superoxide dismutase, catalase, guaiacol peroxidase, low proteolytic activity, lower level of protein carbonyls and protein thiolation could serve as a model to depict water deficit tolerance in Indica rice seedlings.     

Brassinosteroids improve photosystem II efficiency,gas exchange,antioxidant enzymes and growth of cowpea plants exposed to water deficit

Water deficit is considered the main abiotic stress that limits agricultural production worldwide. Brassinosteroids (BRs) are natural substances that play roles in plant tolerance against abiotic stresses, including water deficit. This research aims to determine whether BRs can mitigate the negative effects caused by water deficiency, revealing how BRs act and their possible contribution to increased tolerance of cowpea plants to water deficit. The experiment was a factorial design with the factors completely randomised, with two water conditions (control and water deficit) and three levels of brassinosteroids (0, 50 and 100 nM 24-epibrassinolide; EBR is an active BRs). Plants sprayed with 100 nM EBR under the water deficit presented significant increases in Φ_PSII, q_P and ETR compared with plants subjected to the water deficit without EBR. With respect to gas exchange, P _N, E and g _s exhibited significant reductions after water deficit, but application of 100 nM EBR caused increases in these variables of 96, 24 and 33%, respectively, compared to the water deficit + 0 nM EBR treatment. To antioxidant enzymes, EBR resulted in increases in SOD, CAT, APX and POX, indicating that EBR acts on the antioxidant system, reducing cell damage. The water deficit caused significant reductions in Chl a, Chl b and total Chl, while plants sprayed with 100 nM EBR showed significant increases of 26, 58 and 33% in Chl a, Chl b and total Chl, respectively. This study revealed that EBR improves photosystem II efficiency, inducing increases in Φ_PSII, q_P and ETR. This substance also mitigated the negative effects on gas exchange and growth induced by the water deficit. Increases in SOD, CAT, APX and POX of plants treated with EBR indicate that this steroid clearly increased the tolerance to the water deficit, reducing reactive oxygen species, cell damage, and maintaining the photosynthetic pigments. Additionally, 100 nM EBR resulted in a better dose–response of cowpea plants exposed to the water deficit.     

Responses of leaf gas exchange, water relations, and water consumption in seedlings of four semiarid tree species to soil drying

To understand the response patterns to soil drying and the water use properties of commonly reforested trees in the semiarid Loess Plateau region of China, a glasshouse experiment was carried out with the seedlings of four species, i.e., Robinia pseudoacacia, Armeniaca sibirica, Syringa oblata, and Quercus liaotungensis. Severe water stress induced by withholding water resulted in permanent wilting of most of the seedlings pot-cultured with sandy soil in 8–12 days. Predawn and midday leaf water potentials and gas exchange characteristics (e.g., stomatal conductance) in the seedlings did not show marked changes until the volumetric soil water content decreased to about 0.05. As the soil water content decreased further, these physiological parameters rapidly declined, approaching their minimal levels at the stage of permanent wilting. The response of each parameter to soil water content changes was fitted with a non-linear saturation curve. Though the results suggested that the general pattern of responses to soil drying was identical among the species, quantitative differences in drought tolerance and water use properties were detected. Leaf stomatal conductance in R. pseudoacacia and A. sibirica showed earlier responses to reduced predawn leaf water potentials. However, water use characteristics and specific leaf area indicated that these two species consumed more water and may not be as drought tolerant as S. oblata and Q. liaotungensis. These results may provide important information to compare the reforestation species with respect to soil drying.     

Saikosaponin accumulation and antioxidative protection in drought-stressed Bupleurum chinense DC. plants

Dried root of Bupleurum spp. is one of the most popular ingredients in many oriental medicinal preparations. Potted Bupleurum chinense DC. seedlings were subjected to progressive drought stress by withholding irrigation followed by a rewatering phase. The changes in antioxidant system, hydrogen peroxide (H₂O₂), superoxide radicals (O₂^?), and malondialdehyde (MDA) contents as well as saikosaponin a (SSa) and saikosaponin d (SSd) content in B. chinense roots were investigated. Additionally, the antioxidant activity of the roots extract was evaluated. The results showed that B. chinense root appeared highly resistant to water deficit. Both SSa and SSd content increased with the progressive water deficit, however, decreased under severe drought conditions or after water recovery. Moderate drought treatment resulted in 83% increase in SSa content and 22% increase in SSd content compared to the well-hydrated treatment. And increased SSa and SSd content during drought were accompanied by enhanced O₂^? content and superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) activity until severe drought stress. Notably, in vitra antioxidant tests demonstrated that the lipid peroxidation inhibition capacity was positively correlated with the content of SSa and SSd, particularly significant at p = 0.05 with SSd content. These results suggest that B. chinense roots exhibit effective antioxidative protection mechanism to withstand drought stress. And it could be speculated that drought-induced SSa and SSd accumulation in B. chinense roots may be stimulated via active oxygen species, and consequently involve in mitigating the oxidative damage due to its high anti-lipid peroxidation capacity.     

Influence of germination date on Dioon edule (Zamiaceae) seedling tolerance to water stress

Dioon edule seedling mortality is mostly attributed to dehydration by prolonged drought, even when they present xeromorphic characteristics like the adult plants. The effect of germination date (GD) and soil water deficit on seedling tolerance to water stress was assessed. The seedlings germinated and grown from mature seeds every month from December to April GD were selected to evaluate the leaf area, photosynthetic pigment content, crassulacean acid metabolism (CAM) activity, stomatal conductance (gs) and leaflet anatomy at soil water potential (Ψs) of 0.0 MPa (day 1), ?0.1 MPa (day 40), ?1.0 MPa (day 90), ?1.5 MPa (day 130), and a control (0.0 MPa at day 130) to recognize differences due to leaf development. The seedlings shifted from C₃ to CAM cycling when exposed to water stress at Ψs of ?1.0 MPa, like adult plants. The March–April GD seedlings with undeveloped sclerified hypodermis and stomata, presented reduced leaf area, lower Chlorophyll a/b ratio, higher CAM activity and midday partial stomatal closure when reached Ψs of ?1.0 MPa. These have higher probability of dehydration during severe drought (February–April) than those of the December–February GD with similar Ψs. Plants used for restoration purposes must have full leaf development to increase the survival.     

Application of photochemical parameters and several indices based on phenotypical traits to assess intraspecific variation of oat (<Emphasis Type="Italic">Avena sativa</Emphasis> L.) tolerance to drought

Functionality of the photosynthetic system under water stress is of major importance in drought tolerance. Oat (Avena sativa L.) doubled haploid (DH) lines obtained by pollination of F ₁ oat crosses with maize were used to assess the differences in plant genotypic response to soil drought. The investigations were based on the measurements of gas exchange and chlorophyll a fluorescence kinetics. Drought was applied to 17-day-old seedlings by withholding water for 14 days and subsequent plant recovery. Non-stressed optimally watered plants served as controls. Yield components were determined when plants reached full maturity. It was shown differences among the oat lines with respect to drought stress susceptibility (SI) and stress tolerance index mean productivity and drought susceptibility index. Sensitivity to drought of individual DH lines was significantly different, as demonstrated by the correlation between drought susceptibility index and yield components, such as dry weight (GW) or grain number (GN) of the harvested plants. GW and GN were lower in drought-sensitive genotypes exposed to drought stress compared to those resistant to drought. The principal component analysis allow to separate three groups of lines differing in their sensitivity to drought stress and indicated that tolerance to drought in oat has a common genetic background.     

Antioxidant responses to water deficit by drought‐tolerant and ‐sensitive sugarcane varieties

Water deficit is the major yield‐limiting factor of crop plants. The exposure of plants to this abiotic stress can result in oxidative damage due to the overproduction of reactive oxygen species. The aim of this work was to study the antioxidant‐stress response of drought‐tolerant (SP83‐2847 and SP83‐5073) and drought‐sensitive (SP90‐3414 and SP90‐1638) sugarcane varieties to water‐deficit stress, which was imposed by withholding irrigation for 3, 10 and 20 days. The drought‐sensitive varieties exhibited the lowest leaf relative water content and highest lipid peroxidation, hydrogen peroxide (H₂O₂) and proline contents during the progression of the drought‐stress condition. The antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPOX) and glutathione reductase (GR) activities changed according to variety and stress intensity. SP83‐2847 exhibited higher CAT and APX activities than the other varieties in the early stage of drought, while the activities of GPOX and GR were the highest in the other varieties at the end of the drought‐stress period. A Cu/Zn SOD isoenzyme was absent at the end of drought period from the SP90‐3414‐sensitive variety. The results indicate that lipid peroxidation and early accumulation of proline may be good biochemical markers of drought sensitivity in sugarcane.     

Responses of antioxidant defenses and membrane damage to drought stress in fruit bodies of Auricularia auricula-judae

Fruit bodies of Auricularia auricula-judae are often subjected to drought stress and became dormant. The responses of antioxidant defenses and membrane damage to drought stress were investigated in this study. Picked fruit bodies were exposed to sunlight and dehydrated naturally and samples were collected at different levels of water loss (0, 10, 30, 50, and 70 %) for determination of electrolyte leakage (EL); contents of malondialdehyde (MDA), ascorbic acid (AsA) and reduced glutathione (GSH); and activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD). Results showed that membrane permeability (assessed by EL) and membrane lipid peroxidation (MDA content) remained unchanged at all levels of water loss studied. Contents of AsA and GSH showed no change at 0, 10 and 30 % of water loss, however, both of them increased significantly at 50 and 70 % of water loss. SOD activity significantly increased with the rising of water loss from 0 to 30 %, reached the peak at 30 and 50 % of water loss, and then significantly decreased at 70 % of water loss. A gradual increase in POD and CAT activities was observed when water loss rose from 0 to 50 %. As water loss went up to 70 %, POD activity remained the same as that at 50 %, but CAT activity decreased. The results indicate that the increased activities of enzymatic antioxidants (SOD, CAT and POD) and contents of non-enzymatic antioxidants (AsA and GSH) in fruit bodies of A. auricula-judae can effectively scavenge reactive oxygen species, cause no damage to cell membranes as demonstrated by the unchanged EL and MDA content, and contribute to dormancy under drought stress.     

Drought-Stress-Induced Changes in Activities of Superoxide Dismutase, Catalase, and Peroxidase in Wheat Species

Activities of superoxide dismutase (SOD), catalase (CAT), andperoxidase (POD), as well as malondialdehyde (MDA) contentsand solute potentials, were studied in seedlings of seven wheat(Triticum) species (nine genotypes representing three ploidylevels: hexaploid, tetraploid, diploid) subjected to water stressfor 4, 8, and 12 days by withholding water. Solute potentialsof all genotypes were lowered by water stress. In most species,SOD and CAT activities showed an increase or maintenance inthe early phase of drought and then a decrease with furtherincrease in magnitude of water stress. On the contrary, PODactivities and MDA contents greatly increased in response towater stress. Enzymatic activities partly recovered and MDAcontents decreased with rewatering. Under drought, hexaploidwheats had higher POD activities and MDA contents than tetraploidand diploid wheats; solute potentials and activities of SODand CAT, however, were similar among the three groups. Theseresults suggest that water stress alters the equilibrium betweenfree radical production and enzymatic defense reactions in wheatspecies and that hexaploid wheats have less efficient antioxidantsystems (e.g., the ascorbate-glutathione cycle and the nonenzymaticsystem) than tetraploid and diploid wheats. (Received February 9, 1994; Accepted April 22, 1994)     

Cytokinin-producing, plant growth-promoting rhizobacteria that confer resistance to drought stress in Platycladus orientalis container seedlings

One of the proposed mechanisms through which plant growth-promoting rhizobacteria (PGPR) enhance plant growth is the production of plant growth regulators, especially cytokinin. However, little information is available regarding cytokinin-producing PGPR inoculation on growth and water stress consistence of forest container seedlings under drought condition. This study determined the effects of Bacillus subtilis on hormone concentration, drought resistance, and plant growth under water-stressed conditions. Although no significant difference was observed under well-watered conditions, leaves of inoculated Platycladus orientalis (oriental thuja) seedlings under drought stress had higher relative water content and leaf water potential compared with those of noninoculated ones. Regardless of water supply levels, the root exudates, namely sugars, amino acids and organic acids, significantly increased because of B. subtilis inoculation. Water stress reduced shoot cytokinins by 39.14 %. However, inoculation decreased this deficit to only 10.22 %. The elevated levels of cytokinins in P. orientalis shoot were associated with higher concentration of abscisic acid (ABA). Stomatal conductance was significantly increased by B. subtilis inoculation in well-watered seedlings. However, the promoting effect of cytokinins on stomatal conductance was hampered, possibly by the combined action of elevated cytokinins and ABA. B. subtilis inoculation increased the shoot dry weight of well-watered and drought seedlings by 34.85 and 19.23 %, as well as the root by 15.445 and 13.99 %, respectively. Consequently, the root/shoot ratio significantly decreased, indicative of the greater benefits of PGPR on shoot growth than root. Thus, inoculation of cytokinin-producing PGPR in container seedlings can alleviate the drought stress and interfere with the suppression of shoot growth, showing a real potential to perform as a drought stress inhibitor in arid environments.     

Proteomics analysis of sensitive and tolerant barley genotypes under drought stress

Drought is a severe environmental constraint to plant productivity and an important factor limiting barley yield. To investigate the initial response of barley to drought stress, changes in protein profile were analyzed using a proteomics technique. Three-day-old barley seedlings of sensitive genotype 004186 and tolerant genotype 004223 were given two treatments, one with 20 % polyethylene glycol and the second with drought induced by withholding water. After 3 days of treatments, proteins were extracted from shoots and separated by 2-dimensional polyacrylamide gel electrophoresis. Metabolism related proteins were decreased in the sensitive genotype under drought; however, they were increased in the tolerant genotype. Photosynthetic related proteins were decreased and increased among the three sensitive and three tolerant genotypes, respectively. In addition, amino acid synthesis and degradation related proteins were increased and decreased among the three tolerant genotypes. These results suggest that chloroplastic metabolism and energy related proteins might play a significant role in the adaptation process of barley seedlings under drought stress.     

Impact of osmotic stress on physiological and biochemical characteristics in drought-susceptible and drought-resistant wheat genotypes

In this study, the seedlings of two wheat cultivars were used: drought-resistant Chinese Spring (CS) and drought-susceptible (SQ1). Seedlings were subjected to osmotic stress in order to assess the differences in response to drought stress between resistant and susceptible genotype. The aim of the experiment was to evaluate the changes in physiological and biochemical characteristics and to establish the optimum osmotic stress level in which differences in drought resistance between the genotypes could be revealed. Plants were subjected to osmotic stress by supplementing the root medium with three concentrations of PEG 6000. Seedlings were grown for 21 days in control conditions and then the plants were subjected to osmotic stress for 7 days by supplementing the root medium with three concentrations of PEG 6000 (D1, D2, D3) applied in two steps: during the first 3 days of treatment ?0.50, ?0.75 and ?1.00 and next ?0.75, ?1.25 and ?1.5 MPa, respectively. Measurements of gas exchange parameters, chlorophyll content, height of seedlings, length of root, leaf and root water content, leaf osmotic potential, lipid peroxidation, and contents of soluble carbohydrates and proline were taken. The results highlighted statistically significant differences in most traits for treatment D2 and emphasized that these conditions were optimum for expressing differences in the responses to osmotic stress between SQ1 and CS wheat genotypes. The level of osmotic stress defined in this study as most suitable for differentiating drought resistance of wheat genotypes will be used in further research for genetic characterization of this trait in wheat through QTL analysis of mapping population of doubled haploid lines derived from CS and SQ1.