The Photosynthetic Characteristics Of Rubisco Activase Transgenic Rice Under Heat Stress

Rice belongs to the thermophilic crops, but high temperature also cuases some damage to its growth and development. When the environment temperature is higher than the optimum temperature for its growth and development, rice will meet with high temperature stress. High temperature stress inhibits rice photosynthesis, reduce its production. So study on effect of heat stress on plant photosynthesis mechanism becomes very important. In this experiment, we took wild type rice plant (WT), Rubisco activase large isoform and Rubisco activase small isoform(RCAL,RCAs) over expression transgenic rice plant and RCA antisense strain (anti-rca) as materials, and investigated into the gas exchange parameters, chlorophyll fluorescence and P700, RCA content and relative expression of RCA under the high temperature stress. The experimental results show that, under high temperature stress, the photosynthesis inhibition degree of RCAs-over and RCAL-over is lower than that of the WT, the photosynthesis inhibition degree of anti-rca is higher than that of the WT. The differences in photosynthesis of four rice lines under high temperature stress are not caused by the stomatal factors. Through the study of high temperature stress on the chlorophyll fluorescence parameters (Fv/Fm, Fv’/Fm’, ETRII, qP, NPQ) and P700parameters (ETRI), we found that the net photosynthetic rate of all rice lines have obviously decreased at fisrt day with high temperature treatment, however, Fv/Fm, F’v/F’m, ETRI, ETRII, qP, NPQ of the three lines (RCAs-over, the RCAL-over and WT) have no significant change. ETRII and qP parameters of anti-rca mutant, in three days after high temperature treatment, had significant difference with WT. The above shows that the effect of short-term moderate high temperature stress (40℃) on photosynthesis is not due to damage of photosystem Ⅱ. The photosystem of the anti-rca is more sensitive to short-term high temperature stress than the other three lines, perhaps it contains less RCA level. The experiment of the high temperature stress and recovery period showed that the trend of RCA content change of four lines is similar to the trend of the photosynthetic rate. The differences of photosynthetic rate between four different rice lines can be explained by the difference in RCA protein between those. We inferred that the decrease in RCA content is one of the main reasons of low photosynthetic rate. The change of protein content may be associated with gene relative expression level and protein metabolism. In order to further clarify the reason for difference in protein content of them under high temperature stress and recovery period, we analyzed the mRNA of different rice lines responding to high temperature. Results showed that the change of mRNA was not matched with the change of RCA protein contents of four rice lines, meaning that the change of RCA protein contents is not caused by the changes in concentrations of RCA gene relative expression. Therefore we inferred that RCA protein content under high temperature stress change is determined after the transcription level.