Relationship Between Rubisco Activase And Drought Tolerance In Rice (Oryza Sativa)

Ribulose-1,5-bisphosphate carboxylase/oxygenase(Rubisco)catalyzes the first step of both the photosynthetic carbon assimilation and photorespiratory carbon oxidation,and is a key regulatory enzyme of photosynthesis.The catalytic sites of Rubsico need to be activated by the carbamylation of a lysine residue with the sites follwed by binding of magnesium.In this experiment the relationship between the anti-sense mutant rice reduced in Rubisco activase(RCA) and drought tolerance was conducted,and additionally the over-expression rice with large or small isoform of rca has been obtained with gene transformation.The results are as follows:The antisense rca plants and its wild type(Oryza.Sativa L.ssp.japonica)were used for studying the effects of drought on the gas exchange parameters,chlorophyll fluorescence parameters,chlorophyll content,Rubisco activity,Rubisco content and RCA content in them.The results showed that photosynthesis was suppressed to a more degree in antisense rca plants than in wild type,and it was mainly due to the non-stomatal limitation.The Rubisco activity,Rubisco content,chlorophyll content,F_v'/F_m' andΦ_PSⅡdecreased at a higher speed in antisense rca plants than in the wild type.All those did no favor for normal operation of Calvin Cycle and PSⅡactivity.The large isoform and small isoform mRNA of Rubisco Activase(RCA)gene(rca)were amplified using specific primers and inserted into pUCmT vector,and then cut with HindⅢ/BamHⅠafter confirmed by sequencing.The fragments were inserted into the binary expression vector pCAMBIA1390-ubi,and the resulting construction with overexpression rca were named pC1390-Ⅰ(RCAⅠ)and pC1390-Ⅱ(RCAⅡ).The pC1390-Ⅰand pC1390-Ⅱvector were introduced into Agrobacterium tumefaciens strain EHA105 by electroporation and transformed to embryos of rice(Oryza.sativa L.ssp.japonica)cultivar Zhonghua11 via Agrobacterium tumefaciens system.Plantlets were regenerated in vitro by resistance selection on medium containing various concentrations of hygromycin.Both GUS histochemical assays and PCR amplification demonstrated that antisense rca was integrated into T0 genomes and inherited to T1. The result of RCA content measurement showed that,the overexpression plants increased approximately 30%of the wild-type level.This has set a base for uncovering the function of RCA in tolerance of plant to drought stress.