Comparative changes in the physiological traits in the flag leaf of two senescing varieties of wheat (Triticum aestivum L.)

Yield gains in wheat are a result of greater plant photosynthetic efficiency and better ability to tolerate biotic or abiotic stresses due to the protection of photosynthetic structures from reactive oxygen species (ROS) by efficient antioxidative system. The slower rate of senescence could be associated to higher grain yield. The objective of this study was to identify antioxidative signalling in two different winter wheat varieties which regulates the process of senescence. Concentration of malondialdehyde (MDA) and hydrogen peroxide (H2O2) content, activities of the antioxidant enzymes (catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.11), guaiacol peroxidase (GPOD; EC 1.11.1.7) and polyphenol oxidase (PPO; EC 1.14.18.1)), chlorophyll (Chl) and carotenoid (Car) concentration as well as photosynthetic efficiency in the flag leaves were determined. Results showed that compared to high-quality variety (Olimpija), Kraljica (high-yielding variety) increased CAT, APX, GPOD and PPO activities earlier during the course time experiment, which could be the reason of delayed senescence process. Oxidative damage resulting from increased H2O2 accumulation with increased lipid peroxidation and a decline in antioxidative enzymes activity may contribute to accelerated senescence in Olimpija. Furthermore, delay in senescence in Kraljica was associated with a decrease in the grain protein content. As a result of declination in Chl a + b and carotenoid content, MDA concentration in the flag leaves of Olimpija gradually increased at each sampling point with decline in antioxidant enzymes activity. However, the rate of protein and chlorophyll degradation occurs normally below the green tissue where Kraljica maintained higher chlorophyll level longer then Olimpija.