Abstract:

In the present work，we investigated the effects of 24-epibrasinolide on growth，activities of photosynthetic enzymes and their gene expressions in low-light sensitive tomato‘Jiersi’leaves under low light stress. The results showed that low light stress significantly reduce the weight，stem diameter and seedling index by 70.5%，13.0% and 77.7% as compared to the control，respectively，but increased plant height by 45.3%. Application of EBR significantly alleviated the low light stress induced-inhibition of growth in seedlings. Under low light，the net photosynthetic rate（P_n）was reduced by 42.8% as compared with the control，while P_n increased by spraying EBR to 72.0% of the control. Low light stress significantly decreased of ribulose-1,5-bisphosphate carboxylase（Rubisco），Rubisco activating enzyme（RCA），fructose-1,6- bisphosphate aldolase（Ald），and fructose-1,6-phosphatase（FBPase）by 41.6%，31.3%，31.4%，and 19.6%，respectively. EBR significantly increased these enzymes activities of photosynthesis under low light stress. Moreover，the mRNA expressions of RbcL，RbcS，RCA，Ald，FBPase，GAPDH，TK，SBPase，and PRK were significantly decreased. EBR significantly improve the low light stress-mediated changes of aforementioned mRNA transcripts，which mRNA transcription of SBPase and GAPDH towarded the control values. Transcriptional levels of TK and PRK under low light stress plus EBR were higher than the control ones. These results suggest that EBR could improve photosynthetic capacity through regulating gene expression and activity of key enzymes for carbon assimilation，thus confers tolerance to low light stress on tomato plants.

Key words: tomoto, low light stress, brassinolides, growth, photosynthetic enzyme, gene expression