| Tea plant(CameIlia Sinensis (L.) O. Kuntzes) is one of the important industrial crops and export agricultural products in China. The scope of climate which tea areas distributes is between the tropical monsoon climate zone and warm temperate zone in China, and the topography is complex , with plains, hills, high mountains and plateaus. The stress conditions, including strong light intensity, seasonal drought, high or low temperature, often happen in tea areas, additionally, tea plant has habits and characteristics of resisting shade and tending to humid , which leads to photoinhibition of tea plant more easily, and decreases the yield and quality of tea. However, no report of photoinhibition and photoprotection in tea plant is found. At present, the role of xanthophyll cycle in plant photoprtect and the regulation of its key enzyme, violaxanthin de-epoxidase (VDE), are hot spot of study focused on. People mainly utilize methods of molecular biology to study xanthophyll cycle, despite of involving in many other methods. But, up to now, the cDNA of VDE gene and the features of VDE protein in xylophyta yet have not been found. In addition, it is unknown that whether lipocalin protein domain in VDE has functional signification with respect to catalytic activity.Here we place emphasis on studying two aspects in tea plant (cultivars: Fuding-dabaicha and longjing 43): one is of the photoinhibition and its recovery, the role of xanthophyll cycle in photoprotection and the characteristics of it contents change in nature light and in stress conditions, another is of the cloning, analysis with bioinformatics, site-mutated, expression and identification of activity in vitro of the cDNA of VDE gene. All of these further expend the theory of tea plant photosynthesis, and open new opportunities for possible enhancing stress conditions tolerance and photosynthetic efficiency in cultivation and breeding of tea plant. At the same time, these supply the references for the studies on VDEs in other xylophyta, further perfect the theory of plant photoinhibition and give more conclusive evidences for the important position of xanthophyll cycle in plant photoprotection. The significant results are showed as following:, 1. With increase of photon flux density(PFD) since 8:00, photochemical efficiency of PS II(Fv/Fm) of intact conjoined leaves of tea plant decreased gradually, andreached the lowest at 13:00, with Fv/Fm s of Fuding-dabaicha(FD) and Longjing 43(LJ) at 13:00 being lower by 7.9% and 10.2% than these at 8:00 respectively, at the same time, apparent quantum yield(AQY) of tea plant decreased notably after exposed to midday high irradiance, with AQYs of FD and LJ at 14:00 being lower by 25.7% and 28.9% than these at 9:00 respectively, under natural light in sunny day without other stress conditions. it indicates that photoinhibition of photosynthesis often occurs in tea plant under natural high light intensity. Fv/Fm s and potential activities of PS II (Fv/Fo)of FD and LJ decreasing when PFD at 1250 u mol.m-2.s-1 indicate photoinhibition of photosynthesis occurs in tea plant easily. The occurrence of photoinhibition with no decreases of stomatal conductance(Gs) and intercellular CO2 concentration(Ci) shows that natural high light intensity is the essential cause of photoinhibition in tea plant. The extent of photoinhibition of leaf disks of tea plant became more serious with the time of strong light treatment extending, with Fv/Fm s of FD and LJ decreased by 25.0% and 26.2% respectively, and FV/Fo s of FD and LJ decreased by 65.1% and 67.5% Respectively, after exposed to high artificial light intensity for 160 minutes. It indicates that the photoinhibition only caused by strong light is reversible , with the facts that Fv/Fm went up gradually after 13:00,and was close to the maximum at 18:00 in nature, and that Fv/Fm nearly reached to the untreated(control) after recovery of 2~4h in weak light in artificial light.Drought not only made the extent of photoinhibition of tea plant serious but also made the ability...
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