Response Of Photosynthetic Characteristics To The Change Of Light Intensity After Removing Shading In Different Wheat Cultivars And Their Hybrids

There was always with shading problem at late growth period of winter wheat. To explore the mechanism of photo synthetic characteristics to the change of environmental light intensity in wheat, the gas exchange, chlorophyll fluorescence, chlorophyll content, RCA expression, content of soluble sugar and starch, activities of antioxidative enzymes, and malondialdehyde (MDA) content in flag leaves of Xiaoyan54(XY54) and8602, and their hybrids, Xiaoyan81(XY81) and212were assayed after10days of shade treatment (about40%of sunlight) and then exposed to full sunlight from heading to anthesis. The main results are as follows:(1) After10days of shading treatment, the total chlorophyll contents increased and the chlorophyll a/b decreased in all cultivates and then recoverd to CK after removing shading generally. The change was more severely in the hybrid line212. The recovery of Pn in XY81and8602was more rapidly than that in two other cultivates after ceasing shading. The intercellular CO2concentration (Ci) decreased at first and then increased, which showed that both the stomatal and the non-stomata factors had impacts on decreasing photosynthesis.(2) The RCA expression was decreased under shading treatment and then increased after the shading ended. The parent XY54and hybrid212were more sensitive to the change of environmental light. The relative change of RCA expression was a self-regulating mechanism of wheat to adapt the decrease of Pn, which is result from the change in environment light intensity.(3) The content of MDA and the activities of antioxidative enzymes were higher than CK after the shading ended, which suggested that shading and shading removal improved the degree of membrane lipid peroxidation. And there is no different in the activities of antioxidative enzymes between the parents and their hybrids. (4) Although XY54was of strong cold and drought stress tolerance, the adaptability to the change of environment light was not as well as XY81and8602. The higher OPSII and RCA expression are the reasons of the higher Pn in XY81, which shown that the hybrid line XY81has not only high photosynthetic rate which come from parent8602, but inherit strong stress resistance from parent XY54.(5) The contents of water soluble carbohydrate and starch in flag leaves were both decreased during shading, and the decrease in starch was more obvious. The content of water soluble carbohydrate and starch were still lower than CK even the Pn was recovered at the tenth day after the shading ended, suggesting that prophase low light stress could promote the photosynthetic assimilation transfer later.(6) Shading treatment from heading to anthesis has more serious effect on kernels per spike than1000-kernel mass in winter wheat. The effect of low light on the yield of hybrid XY81is lighter than other cultivates.