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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 CO2 assimilation and quantum yield of PSII (ΦPSII). Treatment of brassinazole (Brz), a specific inhibitor for BR biosynthesis, reduced plant growth and at the same time decreased CO2 assimilation and ΦPSII. 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.

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A sat :

Light-saturated rate of CO2 assimilation







C i :

Intercellular CO2 concentration






Fructose-1,6-bisphosphate aldolase




Fructose 6-phosphate


Maximum quantum yield of PSII


Efficiency of energy capture by open PSII


Stomatal conductance

J max :

Maximum RuBP regeneration rates


Ribulose-5-phosphate kinase


Photochemical quenching coefficient


Rubisco large subunit gene


Rubisco small subunit gene

rca :

Rubisco activase gene


Ribulose-1,5-bisphosphate carboxylase/oxygenase




Ribulose phosphate epimerase






Sedoheptulose 7-phosphate


Triose-3-phosphate isomerase

V c,max :

Maximum Rubisco carboxylation rates


Quantum yield of PSII


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This work was supported by the National Basic Research Program of China (2009CB119000), National Natural Science Foundation of China (3050344; 30671428) and the Program for Promotion of Basic Research Activities for Innovative Bioscience (PROBRAIN). We thank Dr J Hong for help with the immunogold-labeling experiment.

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Correspondence to Jing-Quan Yu.

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Xia, XJ., Huang, LF., Zhou, YH. et al. Brassinosteroids promote photosynthesis and growth by enhancing activation of Rubisco and expression of photosynthetic genes in Cucumis sativus . Planta 230, 1185–1196 (2009).

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  • Cucumber (Cucumis sativus)
  • Immunogold labeling
  • Productivity
  • Rubisco activase
  • Sugar metabolism