Physiological Function Of Chloroplastic NAD(P)H Dehydrogenase Under Low Temperature And Its Response To Light Quantity

Chilling-sensitive plant cucumber (Cucumis sativus L.), Jinyan No.4, was used as materialsto investigate the effects of chilling temperature (4℃) in the low light (100 μmol m-2 s-1) onphotoinhibition of photosystem I (PSI) and photosystem II (PSII) and their relationship inchilling-sensitive plants. Wild-type tobacco (Nicotiana tabacum c.v. Xanthi) (WT) and its amutant in which ndh genes were defected were used to study physiological function of cyclicelectron transport around PSI mediated by chloroplastic NAD(P)H dehydrogenase complex(NDH) upon exposure to chilling stress in the low light. Furthermore, primary investigationfor the relationship between growth difference and plant endogenous hormones of cucumberseedlings cultured under sulfur lamp or xenon lamp. The main results are as follows:1. Photosynthesis,photoinhibition and its protective mechanism of cucumber leavesduring chilling stress in the low lightPhotosynthetic rate decreased in cucumber leaf discs during chilling stress and decrease innet photosynthetic rate (Pn) and stomatal conductance (Gs) were accompanied by increase inintercellular CO2 concentration (Ci) and decrease in the carboxylation efficency (CE). Itsuggested that decrease of Pn caused by chilling temperature in the low light is mainly 4山东农业大学博士论文attributed to non-stomata factor. Net photosynthetic rate significantly decreased when leaveswere treated in the light compared to those in the dark. The results of elecreon transport rates in the cucumber thylakoikd indicated that electrontransport activities of PSII ,PSI and the whole electron chain had a descend trend. Theelectron transport activities of PSII were inhibited in the cucumber upon expouse to chillingstress in low light or in the dark, decreased by 30.8% and 27.7%, respectively. The electrontransport activities of PSI decreased by 44.2% after 6h chilling stress in the low light, and itonly decreased by 14.9% in the dark. The electron transport activities of the whole electrontransport chain decreased by 30.1% and 17.4% after chilling stress in the low light and in thedark, respectively. It suggested that chilling stress in the low light results in more severephotoinhibition of PSI compared to PSII and the whole electron transport chain. We analyzed effects of chilling stress on parameters of chlorophyll fluorescence incucumber leaves. After 6h chilling stress in the low light, Fv/Fm had little changes. ΦPSII andqP had a significant descend trend upon exposure to chilling stress in the low light, however,they changed little under chilling stress in the dark. NPQ increased markedly,implying that itresulted in excess excitation energy because chilling temperature inhibited CO2 assimilationin the cucumber leaves even in the low light. Dependent-xanthophyll cycle NPQ could protectplants from further photodamage under the chilling stress in the low light. In addition, chilling stress in the low light could cause the decrease of the contents of AsA ,activities of SOD in the cucumber leaves and activities of APX in the cucumber thylakoid,which in turn led to the accumulation of H2O2, and finally caused lipids peroxidation ofcucumber leaves, accompanied by the increase of MDA and electrolytic leakage.2. Physiological function of chloroplast NAD(P)H dehydrogenase of tobacco underchilling stress in the low light After expoused to chilling temperature(4℃) and weak light(100μmol m-2 s-1) for 6 h,far-red light (FR)-oxidizable P700 had a different degree of decrease in the WT and thetransformant plants of tobacco in which ndhCJK genes were insertionally inactivated(?ndhCJK). However, a lower far-red light (FR)-oxidizable P700 was found in ?ndhCJK 5段伟:低温条件下叶绿体 NAD(P)H 脱氢酶复合体的生理功能及其对光质的响应mutant than in WT. Since the lower FR-oxidizable P700 was almost recovered by addition ofelectron acceptor -methyl vio...