Changes In Photosynthesis During Rice Leaf Senescence Of Low Chlorophyll B Mutant And The Purification Of Calvin Cycle Multienzyme Complex In Chloroplast

Photosynthesis is the basis of growth and development of plant and it provides the substrates and energy for plant.In agricultural production,premature senescence caused the decline of crop productivity.Rice is one of the most important crops in China,Therefore,it is important to improve photosynthesis and increase productivity by delaying the premature senescence and extending the photosynthesis function period.Low chlorophyll b rice mutant and its wild type(Zhenhui 249)were used to study the effects of low chlorophyll b content on senescence of rice leaf by measuring photosynthesis, chlorophyll fluorescence parameters and relative content of Rubisco.The results showed that after full expansion of leaves of the mutant and the wild type,photosynthesis, chlorophyll fluorescence parameters and relative content of Rubisco decreased significantly, qN increased.The net photosynthetic rate of the mutant was higher than that of the wild type.While there was little difference of chlorophyll fluorescence parameters between the mutant and the wild type,the decline of the relative Rubisco content was faster in wild type than in the mutant,so the effects of low chlorophyll b on senescence of the fifth leaf of rice was probably focused on carbon assimilation stage.Low chlorophyll b rice mutant and the wild type rice were adopted to investigate the changes in oxygen evolution,content and sensitivity to trypsin proteolysis of Rubisco LSU during leaf senescence,as well as the effects of antioxidant and oxidant on degradation of Rubisco LSU.The results showed that after full expansion of leaves from the mutant and the wild type,oxygen evolution,relative content of Rubisco LSU declined significantly. The antioxidants could slow the process,while oxidants accelerate.The oxygen evolution rate of the mutant was higher than that of the wild type.The degradation of the relative content of Rubisco LSU was slower in the mutant than in wild type,sensitivity to trypsin proteolysis of Rubisco LSU was lower in the mutant than in wild type,suggest that ROS regulates degradation of Rubisco LSU.The Calvin cycle multi-enzyme complex condidate was purified through ammonium sulfate precipitation,gel filtration and ion exchange chromotagraphy.The candidate had R5P-dependent CO₂ fixation activity with molecular weight of 520kDa and 230kDa.