Pre-anthesis high-temperature acclimation alleviates damage to the flag leaf caused by post-anthesis heat stress in wheat.

The objective of this study was to investigate the effect of pre-anthesis high-temperature acclimation on leaf physiology of winter wheat in response to post-anthesis heat stress. The results showed that both pre- and post-anthesis heat stresses significantly depressed flag leaf photosynthesis and enhanced cell membrane peroxidation, as exemplified by increased O₂⁻(·) production rate and reduction in activities of antioxiditave enzymes. However, under post-anthesis heat stress, plants with pre-anthesis high-temperature acclimation (HH) showed much higher photosynthetic rates than those without pre-anthesis high-temperature acclimation (CH). Leaves of HH plants exhibited a higher Chl a/b ratio and lower chlorophyll/carotenoid ratio and superoxide anion radical release rate compared with those of the CH plants. In addition, antioxidant enzyme activities in HH plants were significantly higher than in CH. Coincidently, expressions of photosythesis-responsive gene encoding Rubisco activase B (RcaB) and antioxidant enzyme-related genes encoding mitochondrial manganese superoxide dismutase (Mn-SOD), chloroplastic Cu/Zn superoxide dismutase (Cu/Zn-SOD), catalase (CAT) and cytosolic glutathione reductase (GR) were all up-regulated under HH, whereas a gene encoding a major chlorophyll a/b-binding protein (Cab) was up-regulated by post-anthesis heat stress at 10 DAA, but was down-regulated at 13 DAA. The changes in the expression levels of the HH plants were more pronounced than those for the CH. Collectively, the results indicated that pre-anthesis high-temperature acclimation could effectively alleviate the photosynthetic and oxidative damage caused by post-anthesis heat stress in wheat flag leaves, which was partially attributable to modifications in the expression of the photosythesis-responsive and antioxidant enzymes-related genes.