Abstract: Using ‘Jinyou 3’ cucumber seedlings as test materials, this paper studied their photosynthetic rate (P_n), Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) and Rubisco activase (RCA) activities, and gene expression of Rubisco and RCA under optimal temperature and weak light (WL: 25 ℃/18 ℃, 100 μmol·m^-2·s^-1), suboptimal temperature and weak light (ST+WL: 18 ℃/12 ℃, 100 μmol·m^-2·s^-1), and low temperature and weak light (LT+WL: 10 ℃/5 ℃, 100 μmol·m^-2·s^-1). Comparing with the control (25 ℃/18 ℃, 400 μmol·m^-2·s^-1), treatments WL, ST+WL, and LT+WL all led to a remarkable decrease in leaf area and dry matter mass. At initial stage, the P_n, Rubisco activity, rbcL and  rbcS expression, RCA activity, and CsRCA expression in the three treatments declined by a big margin; 5-7 days later, these parameters tended to be less changed in treatment WL, ascended slowly in treatment ST+WL, and decreased continuously in treatment LT+WL. These results suggested that the photosynthetic apparatus of test cucumber seedlings could gradually adapt to weak light or suboptimal temperature and weak light. The Rubisco and RCA activities and the gene expression of Rubisco and RCA showed the similar responses to low temperature and weak light as the P_n, suggesting that the decline in Rubisco and RCA activities and gene expression in cucumber seedlings under low temperature and weak light  could be the important reason leading to the decrease of P_n.

Key words: Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), Rubisco activase (RCA, gene expression, low temperature and weak light, suboptimal temperature and weak light, cucumber, calcium cyanamide, continuous cropping obstacles, soil microbial biomass carbon, soil microbial biomass nitrogen, soil enzyme activity.