Response To Low Temperature And Low Light Intensity Of Rubisco And Rubisco Activase In Cucumber

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is the key enzyme of photosynthesis in plants. The catalytic sites of Rubsico need to be activated by carbamylation follwed by binding of Mg²⁺. The activation of Rubsico is regulated by Rubisco activase (RCA) in vivo. Changes of activities and gene expression of Rubisco and RCA in in'Jinyou 3'cucumber seedlings under low temperature and light intensity, characteristics of activities and gene expression of Rubisco and RCA of cucumber in solar-greenhouse were investigated. The main results are as follows:1. ST+LL and LT+LL treatments all led to a remarkable decrease in leaf area and dry matter. Their Pn, Rubisco activity, rbcL and rbcS expression, RCA activity and CsRCA expression declined by a big margin on early treating days. 5⁷ days later, the Pn, activities and gene expression of Rubisco and RCA ascended slowly in ST+LL treatment seedlings, whereas decreased sustaindly in LT+LL treatment seedlings. These data suggested that photosynthetic apparatus in cucumber seedlings have adaptation mechanism to suboptimal temperature and low light intensity. The activities and gene expression of Rubisco and RCA showed a similar response to low temperature and light intensity with Pn. This indicated that the decline in activities and gene expression of Rubisco and RCA in cucumber seedlings under low temperature and light intensity were important reasons wihich led to decrease in Pn.2. Pn and RCA activity of cucumber seedlings were declining as photon flux density (PFD) decreased under optimal temperature. 100μmol·m^-2·s^-1 low light led to significant decrease in Rubisco initial and total activity. However, 300μmol·m^-2·s^-1 suboptimal light did not remarkably affect Rubisco activity. rbcL mRNA expression were increasing, while rbcS expression were declining with PFD decreased. Seedlings subjected to low and suobptimal light showed a significantly higher CsRCA expression ^than control seedligns. Chl b content increased, while Chl a/b decreased in seedlings treated under low light intensity. However, suboptimal light did not affect pigment content.3. Pn of cucumber leaves in solar-greenhouse showed an obviously seasonal change. From Sep.17^th to Dec.20^th, a positive correlation was observed among Pn, PFD and Ta. Activities of Rubisco and RCA, relative expression of rbcL,rbcS and CsRCA showed similar rule to Pn.4. The diurnal variation of Pn of cucumber leaves in solar-greenhouse on May 20^th, sunny day, were double-peak pattern curve, and ^the peaks appeared at 11:00 and 13:00. The diunal variation of Rubisco total activity showed single-peak pattern carve, and the peak appeared at 12:00. It shows that there is a midday depression of photosyn^thesis in existence. However, that of Rubisco initial activity was double-peak pattern curve, the peaks appeared at 12:00 and 16:00. The RCA activity changed calmely at midday period. The relative expression of rbcL of cucumber leaves in solar-greenhouse showed an single-peak pattern curve in diurnal variation, and ^the max appeared at 16:00. however, those of rbcS and CsRCA were double-peaks pattern curve, there peaks appeared at 12:00 and 16:00.5. Pn, activities of Rubisco and RCA in mid-position (4^th to 8^th) leaves of cucumber in solar-greenhouse were higher significantly than those of lower and upper position leaves. The relative expression of rbcL in 4^th, 8^th, 12^th, and first leave were decreasing in turn, that of rbcS in 4^th, the first, 8^th, and 12^th were decreasing in turn. The gene expression of CsRCA in cucumber leaves were increasing with leave position declined.6. A 562bp gene fragment was cloned by RT-PCR, and a prokaryotic expression vector was constructed. The 27.15kD specific protein was induced by IPTG. This work was the base of analysis in protein level expression of Rubisco and RCA in cucumber.