Effect Of High Temperature Stress On Photosynthesis Of Two Wheat Varieties With Different Thermo-tolerence

Heat stress is the one of the factors to suppress the growth and development of wheat. Photosythesis is highly sensitive to high temperature. Heat stress affects plant photosythesis and inhibits the crop yield. Thus, it is important to study the physiological and molecular mechanism of photosynthetic apparatus of wheat respond to heat stress for the high yield of wheat in tropical and subtropical areas.In this study, we contrasted the heat tolerance of photosynthetic apparatus in the thermo-tolerant wheat(Triticum aestivum L.) Ilona and the thermo-sensitive wheat Torysa to investigate the thermoresistant mechanism of photosynthetic apparatus. Meanwhile, we tested the genes in the themo-tolerant wheat Ilona response to heat stress with Gene Expression Chips. The differential expressed genes, pathways response to heat stress and possible protein interaction were analyzed, which revealed the complex gene regulatory network of wheat under heat stress. The main results are as follows:(1) Heat stress decreased the net photosynthetic rate(Pn) and the photochemical efficiency, and increased the ion leakage, MDA content and osmotic adjustment substances content. Under heat stress, compared to Torysa, Ilona maintained higher Pn,photochemical efficiency, osmotic adjustment substances content and lower ion leakage and MDA content.(2) After heat stress, compared to Torysa’s, the O-J-I-P curves of Ilona showed significantly less change. And the chlorophyllfluorescence parameter in Ilona showed obviously higher RC/CS and lower VJ and δRo. After heat stress, Ilona showed higher φPo, ψo and φEo, and showed lower φDo than Torysa.(3) Heat stress lead to the decrease of the activities of key enzymes in the calvin cycle. Compared to Toysa, Ilona maintained higer activities of key enzymes in the calvin cycle.(4) Under heat stress, the content of H2O2 and the production rate of O2·- increased, and the ROS content in Ilona was less than that in Torysa. Meanwhile, Ilona maintained higher level of the autioxidant enzyme activities than Torysa.(5) After heat stress, the the expressions of HSP26.6 were higher than that of Torysa.(6) With the analysis of Gene Expression Chips, we found 5708 differentially expressed genes, including 2318 up-regulated genes, and 3390 down-regulated genes. And we found that heat shock proteins, transcription factors and many pathways, such as carbon fixation, photosynthesis, starch and sucrose metabolism and so on, played important roles in response to heat stress.These results suggested that, under heat stress, Ilona distributed more energy into electron transport chain and maintained higher activities of key enzymes in the calvin cycle to banlance the photosynthetic electron transport and carbon fixation, and as a result inhibited the production of ROS. Besides, the higher autioxidant enzyme activities in Ilona enhanced the scavenging of ROS, and thus reduced the damage to the photosystem under heat stress. When the energy distributed into electron transport was excess, Ilona could dissipate the excess energy by the cyclic electron transport. In addition, the themotolerance of the photosystem in Ilona might be connected with the higher expression of HSP26.6.