Heat-induced oxidative stress and changes in protein profile in wheat cultivars

Abstract

Wheat (Triticum aestivum L.) occupies an important place among cereals and it serves as a staple food for about 35% of the world population. Crop plants experience various stresses during their life cycle under high or low temperature, drought, and salinity conditions. Among these stresses, heat stress is getting alarming as a result of global warming. Therefore, research on the mechanism of high temperature stress in plants has the importance for future generations. The present investigation was aimed at studying the effect of heat stress and revival on antioxidative system and polypeptide pattern in the leaves of wheat seedlings. Four wheat genotypes, i.e., two tolerant (HW-2045 and WH-1021) and two susceptible (HS-277 and WH-147) were selected and the enzymes of antioxidant system, levels of antioxidant metabolites and pattern of polypeptide were observed. The production of H2O2 was higher in the leaves of susceptible and tolerant genotypes under heat stress conditions. However, its level was significantly higher in susceptible as compared to tolerant genotypes. There was enhancement in the activities of antioxidative enzymes, viz. CAT, POX, GR and APX in the leaves of tolerant and susceptible genotypes under heat stress. However, higher per cent increase was observed in tolerant genotypes. Heat stress increased the SOD activity in tolerant genotypes but activity declined in susceptible genotypes. On revival, the activities of the CAT, POX and GR declined in comparison to stressed seedlings but remained higher as compared to control. Accumulation of H2O2, which is a strong oxidant, led to disruption of cellular membrane integrity as obvious from increase in MDA content and an indicator of lipid peroxidation. Higher increase of H2O2 and MDA content was observed in susceptible genotypes which indicate more oxidative stress in the heat susceptible genotypes as compared to heat tolerant genotypes. On revival, accumulation of H2O2 and MDA content was reduced in all the genotypes but their level remained higher than their respective controls. A large number of studies have revealed a positive correlation between induction of HSPs and acquisition of thermotolerance. The most studied effect of heat shock treatment was on the induction of protective heat shock proteins which disappeared on removal of heat stress. In tolerant genotype WH-1021 under stressed conditions five polypeptide bands of MW 103.7, 92.2, 83, 65 and 26 kDa appeared in comparison to unstressed seedlings, while HW-2045 showed five bands of MW 103.7, 98.5, 79, 62 and 26 kDa under heat stress. Both the susceptible genotypes showed similar polypeptide bands of MW 80, 57.9, 45.7 and 34.4 kDa in response to high temperature. The better tolerance character of HW-2045 and WH-1021 during present investigation might be due to the induction of protective heat shock proteins and much higher activities of the enzymes involved in scavenging active oxygen species.