Effects Of High Temperature Stress On Photochemical Activity Of Psii In Tobacco Transformed With Cagpat Gene

Plants often suffer from different kinds of stresses, such as high light, high temperature, low temperature, drought, waterlogging, and so on, which affect plant normal metabolism process. Temperature is the major environmental factor limiting plant growth, development and outputs. In recent years, with the development of agriculture, the large number of emissions of CO₂ enhance the CO₂ concentration in atmosphere and lead to"greenhouse effect". Temperature continues to rise, resulting in reduced crop yield, quality decline and increasingly serious loss in agricultural production. So the effect of high temperature on crop yield and quality has been paid growing attention. The tolerance of plants to environmental stress was closely connected with the fatty acid saturation of plant membrane lipids. The fatty acid saturation of plant membrane lipids is determined by the substrate selectivity of glycerol-3-phosphate acyltransferase (GPAT: EC2.3.1.15), which catalyzes the first step of glycerolipid biosynthesis. Tobacco transformed with sense CaGPAT gene and wild tobacco were taken as materials in our research. We investigated the changes of lipids composistion in thylakoid membrane, effects of high temperature on PSII light absorption and electron transfer capacity and photochemical activity of transgenic tobcco, which provide theoretical reference to improve new varieties of crops by transgenic methods and to improve tolerance to environmental stress. The main results are as follows:1. There is little change in the relative content of membrane lipids of transgenic tobacco. A slight increase in the PG content is discovered. The saturated extent of MGDG, SQDG, DGDG and PG in thylakoid membrane of transgenic tobacco plants increased generally. However, the saturated extent of MGDG increased the most obviously by 16.2%.2. With the increase of stress temperature, Pn, Fv/Fm,ΦPSII, Fv'/Fm'and qP of transgenic tobacco and wild tobacco decreased, and both showed the same trend. There is no obvious difference at 35℃. At 40～48℃, the decrease of Pn, Fv/Fm,ΦPSII, Fv'/Fm'and qP of wild tobacco was more obvious than that of transgenic tobacco, and the most significant difference appeared at 48℃. Under high temperature stress, Fo and NPQ increased more in wild tobacco than that in transgenic tobacco, which indicated that PSII of transgenic tobacco maintained higher photochemical activity to reduce the decrease of photosynthetic rate and increase the tolerance to high temperature.3. In 35 44℃temperature range, the reduction degree and reduction rate of Q_A of transgenic tobacco and wild-type tobacco increased, indicating that the Q_A to Q_B electron transfer is indeed inhibited. The small degree of inhibition of electron transport in transgenic tobacco showed that the tolerance of PSII electron acceptor to high temperature significantly increased after the change of membrane lipid composition. High temperature can injury electron transport, leading to the weakened ability to accept electronic receptor, smaller electron acceptor pool and the decrease of Q_A redox frequency. Results above showed that the tolerance ability of PSII electron acceptor pool to high temperature of wild-type tobacco is less than that of transgenic tobacco.4. Under high temperature stress (48℃), membrane of transgenic tobacco was injuried to a less extent. The change of F_K/F_J,ψo and Fv'/Fm'was less and the value of Fv/Fm andΦPSII maintained in a higher level in transgenic tobacco. This indicated that oxygen evolution complex in the PSII donor side, the electron transport in the acceptor side and the light harvesting complex were less affected in transgenic tobacco under high temperature stress. Therefore, higher photochemical efficiency of PSII could be maintained in the transgenic tobacco under high temperature stress.