Brassinosteroids promote photosynthesis and growth by enhancing activation of Rubisco and expression of photosynthetic genes in Cucumis sativus.
Brassinosteroids (BRs) are a new group of plant growth substances that promote plant growth and productivity. We showed in this study that improved growth of cucumber (Cucumis sativus) plants after treatment with 24-epibrassinolide (EBR), an active BR, was associated with increased CO(2) assimilation and quantum yield of PSII (Phi(PSII)). Treatment of brassinazole (Brz), a specific inhibitor for BR biosynthesis, reduced plant growth and at the same time decreased CO(2) assimilation and Phi(PSII). Thus, the growth-promoting activity of BRs can be, at least partly, attributed to enhanced plant photosynthesis. To understand how BRs enhance photosynthesis, we have analyzed the effects of EBR and Brz on a number of photosynthetic parameters and their affecting factors, including the contents and activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Northern and Western blotting demonstrated that EBR upregulated, while Brz downregulated, the expressions of rbcL, rbcS and other photosynthetic genes. In addition, EBR had a positive effect on the activation of Rubisco based on increased maximum Rubisco carboxylation rates (V (c,max)), total Rubisco activity and, to a greater extent, initial Rubisco activity. The accumulation patterns of Rubisco activase (RCA) based on immunogold-labeling experiments suggested a role of RCA in BR-regulated activation state of Rubisco. Enhanced expression of genes encoding other Calvin cycle genes after EBR treatment may also play a positive role in RuBP regeneration (J (max)), thereby increasing maximum carboxylation rate of Rubisco (V (c,max)). Thus, BRs promote photosynthesis and growth by positively regulating synthesis and activation of a variety of photosynthetic enzymes including Rubisco in cucumber.
Xia
Xiao-Jian
XJ
Department of Horticulture, Huajiachi Campus, Zhejiang University, Hangzhou, People's Republic of China.
Huang
Li-Feng
LF
Zhou
Yan-Hong
YH
Mao
Wei-Hua
WH
Shi
Kai
K
Wu
Jian-Xiang
JX
Asami
Tadao
T
Chen
Zhixiang
Z
Yu
Jing-Quan
JQ
D018533:Biomass; D015153:Blotting, Western; D060406:Brassinosteroids; D002245:Carbon Dioxide / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D002777:Cholestanols / Q000378:metabolism / Q000494:pharmacology*; D018553:Cucumis sativus / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D006601:Hexoses / Q000378:metabolism; D007700:Kinetics; D010788:Photosynthesis / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D010937:Plant Growth Regulators / Q000378:metabolism / Q000494:pharmacology; D018515:Plant Leaves / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics / Q000254:growth & development; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics / Q000378:metabolism*; D013213:Starch / Q000378:metabolism; D013260:Steroids, Heterocyclic / Q000378:metabolism / Q000494:pharmacology*; D013395:Sucrose / Q000378:metabolism; D014230:Triazoles / Q000494:pharmacology
D060406:Brassinosteroids; D002777:Cholestanols; D006601:Hexoses; D010937:Plant Growth Regulators; D010940:Plant Proteins; D013260:Steroids, Heterocyclic; D014230:Triazoles; D002734:Chlorophyll; D002245:Carbon Dioxide; D013395:Sucrose; D013213:Starch; D012273:Ribulose-Bisphosphate Carboxylase; C412342:brassinazole; C023623:brassinolide