Analysis Of The Mechanism Of ABA Regulating Photosynthesis Of Rice In Different Development Stages

In this study, the dynamic changes of the photosynthetic rate and its mechanism of exogenous ABA treatment in different developmental stages of Liangyoupeijiu (LYP9)(tillering, jointing-booting, flowering, grain filling stage) were explored. The main results are as follows:The dynamic changes of photosynthetic rate (Pn) in functional leaves with exogenous ABA (300μmol/L,100μmol/L,30μmol/L) treatment at the four developmental stages was studied using the Li-6400 photosynthesis system. The results showed that the photosynthetic rate decreased significantly when the concentration of ABA treatment increased. The photosynthetic rate of rice at tillering stage was bouncing downward with the low concentration of ABA treatment and eventually dropped to zero after 73min. The response for rice toward exogenous ABA was more and more sensitive when it grew. The rice at tillering stage had the stronger tolerance aganist exogenous ABA. The photosynthetic rate reduced at zero after 11 min with high concentration (300μmol/L) of ABA treatment and after 36 min with middle concentration (100μmol/L) of ABA treatment approximately. The tolerance to exogenous ABA reduced at flowering stage in which the photosynthetic rate dropped to zero after 25min with middle concentration (100μmol/L) of ABA treatment and after nearly 30min with low concentration (30μmol/L) of ABA treatment. At jointing-booting stage, the photosynthetic rate declined to zero after 17min with the middle concentration (100μmol/L) of ABA treatment and after 30min with low concentration (30μmol/L) of ABA treatment. The most sensitive response to exogenous ABA was at grain filling stage because the photosynthetic rate reduced to zero after 16 min approximately with middle concentration (100μmol/L) of ABA treatment and after 29 min approximately with low concentration (30μmol/L) of ABA treatment at this stage. In addition, the research revealed that the photosynthetic rate always had a short period of stress rise at 0.5min with three different concentrations of exogenous ABA treatment, and after that the photosynthetic rate decreased gradually.Determination of the content of endogenous hormone ABA in rice leaves at four developmental stages showed that the content of endogenous ABA was lowest at jointing booting stage and the other three period were similar. Compared with the control, the content of endogenous ABA with ABA treatment increased significantly, respectively 45.6% at tillering stage,77.17% at jointing-booting stage,53.94% at flowering stage and 35.85% at grain filling stage, which showed the expression of genes controlling ABA synthesis in rice were enhanced after the treatment of exogenous ABA, which lead to the increase of the content of endogenous ABA. The determination of leaves chlorophyll content in rice at each stage showed that the chlorophyll content under ABA treatment did not change significantly, indicating that ABA treatment within a short time is insufficient to cause the changes of chlorophyll content.We studied the different protein expressions of rice at four stages with ABA treatment and identified respectively 21,19,20,20 proteins of different expressions at four different stages using differential proteomics. These proteins of different expression which expressed at different stage all involved in photosynthesis, stress, hormone synthesis and transportation and response to the ABA signal transduction, indicating that there was a universal mechanism underlying responding to the ABA in rice. The up-regulation of the proteins related stress indicated endogenous ABA could induced many stress responses in rice so that it could survive under stress condition. The down-regulation of the proteins related photosynthesis showed ABA could affect the expression of enzymes required for photosynthesis to reduce the photosynthetic rate in rice. The effects of the proteins responsed to signal pathways involved in closing the guard cell were consistent though some up-regulated and other down-regulated, indicating that the stomatal closure induce by ABA was one of the main reasons of the decrease of photosynthetic rate.Six genes respectively coding sphingosine kinase, glyoxalase I, formate-tetrahydrofolate ligase, phytochrome C, putative heat shock transcription factor 8 and heat shock protein cognate 70 under ABA treatment were studied by RT-PCR. The result found that the expression of gene coding phytochrome C was significantly decreased only and the expressions of the other five genes were increased, which further showed that ABA could decrease the expressions of genes related photosynthesis and induce stomatal closure to reduce the photosynthetic rate in rice. In addition, ABA could induce a variety of stress responses in rice so that it could survive under stress condition.In summary,ABA treatment promoted the expressions of genes related ABA synthesis, which increased the content of ABA. The determination of leaves chlorophyll content in rice at each stage showed that the chlorophyll content under ABA treatment did not change significantly, which indicated that ABA treatment in a short time is not sufficient for the changes of chlorophyll content. Both the synthesis of enzymes required for photosynthesis and stomatal closure in many signal pathways induced by ABA lead to the decrease of the photosynthetic rate in rice.