R. K. Sairam

Differential response of wheat genotypes to long term salinity stress in relation to oxidative stress, antioxidant activity and osmolyte concentration

Effect of long term soil salinity was studied in wheat cvs, Kharchia 65 (tolerant) and KRL 19 (moderately tolerant) under control and two levels of salinity (ECe � /5.4 and 10.6 dS m � 1 ). Salinity stress decreased relative water content (RWC), chlorophyll (CHL), carotenoids (CAR), membrane stability index (MSI), biomass and grain yield, and increased hydrogen peroxide (H2O2), thiobarbituric acid reactive substances (TBARS), proline, glycine-betaine (GB), soluble sugars, superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR) activity in both the genotypes and at all the stages. Salinity induced decrease in RWC, CHL, CAR, MSI, biomass and grain yield were significantly higher in KRL 19 than more tolerant Kharchia 65. Kharchia 65 recorded higher activity of SOD, CAT, GR, as well as contents of proline, soluble sugar, GB and K, and comparatively lower H2O2 and TBARS contents compared with KRL 19. KRL 19 also showed higher Na and Na/K ratio. Results show that salinity tolerance of Kharchia 65 as manifested by lower decrease in biomass and grain yield is associated with higher antioxidant activity, osmolyte concentration and potassium contents, and lower H2O2, TBARS and sodium contents than KRL 19. # 2002 Elsevier Science Ireland Ltd. All rights reserved.

Oxidative stress and antioxidant activity as the basis of senescence in maize leaves

Abstract Leaf senescence was studied in an early (X 3342) and late (Deccan 103) cultivar of maize. Observations were recorded in the flag leaves with the initiation of tasseling at an interval of 5 days upto the senescent leaf stage. Hydrogen peroxide content and lipid peroxidation increased from young leaf stage to the senescent leaf stage. Chlorophyll content initially increased up to 10th day after tasseling (DAT) and decreased thereafter, while carotenoid content increased up to 30 DAT and then decreased. Activities of superoxide dismutase (SOD), ascorbate peroxidase (APOX), peroxidase (POX) and catalase (CAT) increased up to 20–25 DAT and thereafter, decreased in both the cultivars. Among the SOD isoforms, Mn-SOD activity was highest in the two cultivars and was responsible for the peak in total SOD activity observed at 20–25 DAT. Fe-SOD and Cu/Zn-SOD activities did not vary much at different stages. Late cv. Deccan 103 maintained lower hydrogen peroxide content and lipid peroxidation, and higher activities of superoxide dismutase, specifically Mn-SOD, APOX and CAT and contents of chlorophyll and carotenoids at 40 DAT than early cv. X 3342. The results suggest that leaf senescence in general and early senescence of early cv. X 3342 is associated with higher oxidative stress and a decline in antioxidant activity towards maturity, and Mn-SOD has a major role in the scavenging of superoxide radicals during maize leaf senescence.

Changes in antioxidant activity in sub-cellular fractions of tolerant and susceptible wheat genotypes in response to long term salt stress

Abstract Effects of long term, medium level (electrical conductivity of extract (ECe)=6.85 dS m −1 ) sodium chloride (NaCl) salinity were studied in tolerant (Kharchia 65) and susceptible (HD 2687) wheat genotypes. NaCl salinity caused decrease in relative water content (RWC), chlorophyll (CHL), membrane stability index (MSI) and ascorbic acid (AA) content, and increased the contents of hydrogen peroxide (H 2 O 2 ), thiobarbituric acid reactive substances (TBARS) (measure of lipid peroxidation) and activities of superoxide dismutase (SOD), its various isozymes, ascorbate peroxidase (APOX) and glutathione reductase (GR) in wheat genotypes Kharchia 65 (tolerant) and HD 2687 (susceptible). Salinity tolerant wheat cv. Kharchia 65 showed less decline in RWC, CHL, MSI estimated in whole tissue than salt sensitive HD 2687. Kharchia 65 also exhibited less decrease in AA content, less increase in H 2 O 2 , TBARS contents and higher increase in SOD and its isozymes, APOX and GR in all sub-cellular fractions than salt sensitive HD 2687. H 2 O 2 , TBARS contents and AA contents were higher in chloroplastic fraction. Chloroplastic fraction showed higher total SOD, APOX and GR activity, followed by mitochondrial fraction in case of total SOD and GR, while cytosolic fraction was in second place in case of APOX activity. Though Mn–SOD activity was highest in mitochondrial fraction, but residual activity was also observed in cytosolic fraction. Cu/Zn–SOD and Fe–SOD were observed in all the sub-cellular fractions, however, the activities were higher in chloroplastic fraction for both the isoforms. Total Cu/Zn–SOD activity, sum of activity observed in all the fractions, was higher than other SOD isoforms. Susceptibility of HD 2687 to long-term salinity stress seems to be due to relatively less induction of SOD isozymes, no induction in chloroplastic and mitochondrial APOX and cytosolic GR and decrease in chloroplastic GR under salt stress resulting in higher oxidative stress in the form of H 2 O 2 and TBARS contents and decrease in MSI and CHL.

Differences in antioxidant activity in response to salinity stress in tolerant and susceptible wheat genotypes

Effects of long-term sodium chloride salinity (100 and 200 mM NaCl; ECe = 6.85 and 12.3 dS m−1) were studied in tolerant (Kharchia 65, KRL 19) and susceptible (HD 2009, HD 2687) wheat genotypes. NaCl decreased relative water content (RWC), chlorophyll content (Chl), membrane stability index (MSI) and ascorbic acid (AA) content, and increased the contents of hydrogen peroxide, thiobarbituric acid reactive substances (TBARS), and activities of superoxide dismutase (SOD), ascorbate peroxidase (APOX) and glutathione reductase (GR). Kharchia 65 showed lowest decline in RWC, Chl, MSI and AA content, lowest increase in H2O2 and TBARS contents and higher increase in SOD and its isozymes, APOX and GR, while HD2687 showed the highest decrease in AA content, highest increase in H2O2 and TBARS contents and smallest increase in activities of antioxidant enzymes. KRL 19 and HD 2009 showed intermediate response both in terms of oxidative stress and antioxidant activity.

Protective role of antioxidant enzymes under high temperature stress.

An experiment was conducted to study the effect of high temperature stress on the antioxidant enzyme activity in five wheat genotypes viz., PBW 343, PBW 175, HDR-77, HD 2815 and HD 2865. There was significant increase in the activity of superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT) in the late and very late planting and at all stages of plant growth, i.e., vegetative, anthesis and 15 days after anthesis (DAA), however glutathione reductase (GR) and peroxidase (POX) activity decreased under late and very late plantings compared to normal planting. In general HD 2815, HDR-77 showed relatively higher SOD, APX, GR, CAT and POX activity in the late plantings compared to PBW 343, PBW 175 and HD 2865. Significant reduction in chlorophyll content and increase in membrane injury index were observed in all genotypes with age, and also under late and very late sowings at all the stages of plant growth. However HD 2815 and HDR-77, which showed highest activity of various antioxidant enzymes under late and very late sowing also showed minimum reduction in chlorophyll content and lower membrane injury index, indicating the amelioration of high temperature stress induced oxidative stress by antioxidant enzymes. Various antioxidant enzymes showed positive correlation (r) with chlorophyll content and negative with membrane injury index at most of the stages in the five wheat genotypes.

Increased antioxidant activity under elevated temperatures: a mechanism of heat stress tolerance in wheat genotypes.

An experiment was conducted with three wheat (Triticum aestivum L.) genotypes C 306, HD 2285 and HD 2329 (differently susceptible to water and temperature stress) to study the extent of oxidative injury and activities of antioxidant enzymes in relation to heat stress induced by manipulating dates of sowing. Increase in temperature by late sowing significantly decreased leaf relative water content (RWC), ascorbic acid content, and increased H2O2 content and lipid peroxidation in all the genotypes at 8 and 23 d after anthesis. Temperature tolerant genotypes C 306, closely followed by HD 2285 were superior to HD 2329 in maintaining high RWC, ascorbic acid content, and lower H2O2 content and lipid peroxidation (malondialdehyde content) under high temperature (late sowing) at the two stages. Activities of superoxide dismutase and catalase were highest in HD 2285 followed by C 306 and minimum in HD 2329 while ascorbate peroxidase activity was highest in C 306.

Role of Antioxidant Systems in Wheat Genotypes Tolerance to Water Stress

The role of plant antioxidant systems in stress tolerance was studied in leaves of three contrasting wheat genotypes. Drought imposed at two different stages after anthesis resulted in an increase in H2O2 accumulation and lipid peroxidation and decrease in ascorbic acid content. Antioxidant enzymes like superoxide dismutase, ascorbate peroxidase and catalase significantly increased under water stress. Drought tolerant genotype C 306 which had highest ascorbate peroxidase and catalase activity and ascorbic acid content also showed lowest H2O2 accumulation and lipid peroxidation (malondialdehyde content) under water stress in comparison to susceptible genotype HD 2329 which showed lowest antioxidant enzyme activity and ascorbic acid content and highest H2O2 content and lipid peroxidation. HD 2285 which is tolerant to high temperature during grain filling period showed intermediate behaviour. Superoxide dismutase activity, however, did not show significant differences among the genotypes under irrigated as well as water stress condition. It seems that H2O2 scavenging systems as represented by ascorbate peroxidase and catalase are more important in imparting tolerance against drought induced oxidative stress than superoxide dismutase alone.

Physiology and biochemistry of waterlogging tolerance in plants

Waterlogging is a serious problem, which affects crop growth and yield in low lying rainfed areas. The main cause of damage under waterlogging is oxygen deprivation, which affect nutrient and water uptake, so the plants show wilting even when surrounded by excess of water. Lack of oxygen shift the energy metabolism from aerobic mode to anaerobic mode. Plants adapted to waterlogged conditions, have mechanisms to cope with this stress such as aerenchyma formation, increased availability of soluble sugars, greater activity of glycolytic pathway and fermentation enzymes and involvement of antioxidant defence mechanism to cope with the post hypoxia/anoxia oxidative stress. Gaseous plant hormone ethylene plays an important role in modifying plant response to oxygen deficiency. It has been reported to induce genes of enzymes associated with aerenchyma formation, glycolysis and fermentation pathway. Besides, nonsymbiotic-haemoglobins and nitric oxide have also been suggested as an alternative to fermentation for maintaining lower redox potential (low NADH/NAD ratio), and thereby playing an important role in anaerobic stress tolerance and signaling.

Changes in antioxidant enzymes activity and oxidative stress by abscisic acid and salicylic acid in wheat genotypes

Abscisic acid (ABA) and salicylic acid (SA) were sprayed on leaves of wheat genotypes C 306 and Hira at 25 and 40 d after sowing under moderate water stress (−0.8 MPa) imposed by adding PEG-6000 in nutrient solution. ABA and SA increased the activities of superoxide dismutase, ascorbate peroxidase, glutathione reductase, and catalase in comparison to unsprayed control plants. Both ABA and SA treatments decreased the contents of hydrogen peroxide and thiobarbituric acid reactive substances, a measure of lipid peroxidation, compared to unsprayed plants. The beneficial effect of increase in antioxidant enzymes activity and decrease in oxidative stress was reflected in increase in chlorophyll and carotenoid contents, relative water content, membrane stability index, leaf area and total biomass over control plants. The lower concentrations of ABA (0.5 mM) and SA (1.0 mM) were generally more effective than higher concentrations.

Stress induced injury and antioxidant enzymes in relation to drought tolerance in wheat genotypes

The role of plant antioxidant system in water stress tolerance was studied in three contrasting wheat genotypes. Water stress imposed at different stages after anthesis resulted in a general increase in lipid peroxidation (LPO) and decrease in membrane stability index (MSI), and contents of chlorophylls (Chl) and carotenoids (Car). Antioxidant enzymes like glutathione reductase and ascorbate peroxidase significantly increased under water stress. Genotype C 306, which had highest glutathione reductase and ascorbate peroxidase activity, also showed lowest LPO and highest MSI, and Chl and Car contents under water stress in comparison to susceptible genotype HD 2329, which showed lowest antioxidant enzyme activity as well as MSI, Chl and Car contents and highest LPO. HD 2285 which is tolerant to high temperature during grain filling period showed intermediate behaviour. Thus, the relative tolerance of a genotype to water stress as reflected by its comparatively lower LPO and higher MSI, Chl and Car contents is closely associated with its antioxidant enzyme system.