AOBPreview originally published online on February 14, 2006
Annals of Botany 2006 97(5):739-744; doi:10.1093/aob/mcl025
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Antisense Inhibition of Rubisco Activase Increases Rubisco Content and Alters the Proportion of Rubisco Activase in Stroma and Thylakoids in Chloroplasts of Rice Leaves
1 State Key Laboratory of Plant Physiology and Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou 310029, China, 2 Institute of Biotechnology, Zhejiang University, Hangzhou 310029, China and 3 Department of Chemistry and Biology, Chuzhou University, Chuzhou 239000, China
* For correspondence. E-mail dajiang{at}zju.edu.cn
Received: 1 October 2005 Returned for revision: 3 November 2005 Accepted: 23 December 2005 Published electronically: 14 February 2006
• Background and Aims Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activase (RCA) is a nuclear-encoded chloroplast protein that modifies the conformation of Rubisco, releases inhibitors from active sites, and increases enzymatic activity. It appears to have other functions, e.g. in gibberellin signalling and as a molecular chaperone, which are related to its distribution within the chloroplast. The aim of this research was to resolve uncertainty about the localization of RCA, and to determine whether the distributions of Rubisco and RCA were altered when RCA content was reduced. The monocotyledon, Oryza sativa was used as a model species.
• Methods Gas exchange and Rubisco were measured, and the sub-cellular locations of Rubisco and RCA were determined using immunogold-labelling electron microscopy, in wild-type and antisense rca rice plants.
• Key Results In antisense rca plants, net photosynthetic rate and the initial Rubisco activity decreased much less than RCA content. Immunocytolocalization showed that Rubisco in wild-type and antisense plants was localized in the stroma of chloroplasts. However, the amount of Rubisco in the antisense rca plants was greater than in the wild-type plants. RCA was detected in both the chloroplast stroma and in the thylakoid membranes of wild-type plants. The percentage of RCA labelling in the thylakoid membrane was shown to be substantially decreased, while the fraction in the stroma was increased, by the antisense rca treatment.
• Conclusions From the changes in RCA distribution and alterations in Rubisco activity, RCA in the stroma of the chloroplast probably contributes to the activation of Rubisco, and RCA in thylakoids compensates for the reduction of RCA in the stroma, allowing steady-state photosynthesis to be maintained when RCA is depleted. RCA may also have a second role in protecting membranes against environmental stresses as a chaperone.
Key words: Antisense rca rice plants, Rubisco, Rubisco activase (RCA), cellular localization
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