A role for brassinosteroids in the regulation of photosynthesis in Cucumis sativus.
The effects of 24-epibrassinolide (EBR) spray application on gas-exchange, chlorophyll fluorescence characteristics, Rubisco activity, and carbohydrate metabolism were investigated in cucumber (Cucumis sativus L. cv. Jinchun No. 3) plants grown in a greenhouse. EBR significantly increased the light-saturated net CO(2) assimilation rate (A(sat)) from 3 h to 7d after spraying, with 0.1 mg l(-1) EBR proving most effective. Increased A(sat) in EBR-treated leaves was accompanied by increases in the maximum carboxylation rate of Rubisco (V(c,max)) and in the maximum rate of RuBP regeneration (J(max)). EBR-treated leaves also had a higher quantum yield of PSII electron transport (phi(PSII)) than the controls, which was mainly due to a significant increase in the photochemical quenching (q(P)), with no change in the efficiency of energy capture by open PSII reaction centres (F'(v)/F'(m)). EBR did not influence photorespiration. In addition, significant increases in the initial activity of Rubisco and in the sucrose, soluble sugars, and starch contents were observed followed by substantial increases in sucrose phosphate synthase (SPS), sucrose synthase (SS), and acid invertase (AI) activities after EBR treatment. It was concluded that EBR increases the capacity of CO(2) assimilation in the Calvin cycle, which was mainly attributed to an increase in the initial activity of Rubisco.
Yu
Jing Quan
JQ
Horticultural Department, Zhejiang University, Kaixuan Road 268, Hangzhou, PR China 310029. yu@mail.hz.zj.cn
Huang
Li Feng
LF
Hu
Wen Hai
WH
Zhou
Yan Hong
YH
Mao
Wei Hua
WH
Ye
Su Feng
SF
Nogués
Salvador
S
D060406:Brassinosteroids; D002245:Carbon Dioxide / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D002777:Cholestanols / Q000494:pharmacology*; D018553:Cucumis sativus / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D005740:Gases / Q000378:metabolism; D007700:Kinetics; D010788:Photosynthesis / Q000187:drug effects / Q000502:physiology*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D010937:Plant Growth Regulators / Q000494:pharmacology*; D012044:Regression Analysis; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D013260:Steroids, Heterocyclic / Q000494:pharmacology*
D060406:Brassinosteroids; D002777:Cholestanols; D005740:Gases; D045332:Photosystem II Protein Complex; D010937:Plant Growth Regulators; D013260:Steroids, Heterocyclic; D002734:Chlorophyll; D002245:Carbon Dioxide; D012273:Ribulose-Bisphosphate Carboxylase; C023623:brassinolide