Relationship between Rubisco activase isoform levels and photosynthetic rate in different leaf positions of rice plant

Abstract

To investigate into the relationship between two Rubisco activase (RCA) isoforms and photosynthetic rate, a set of enzyme-linked immunosorbent assay (ELISA) were developed for accurate quantification of two RCA polypeptides based on two specific monoclonal antibodies against different RCA isoforms. The results showed that content of RCA small isoform (RCAS) was 5-fold more than that of RCA large isoform (RCAL) content in all leaves and the RCAL/RCAS ratio reached maximum in the leaf with the highest photosynthetic rate. Although the difference in two RCA polypeptides accumulation in leaves was caused by different transcript level of two isoforms, the decrease of RCAL/RCAS ratio during leaf aging was not attributed to transcriptional regulation. The leaves with higher photosynthetic capacity exhibited higher RCAL/RCAS ratio and the decrease in photosynthetic rate and Rubisco activation state highly correlated with the decline of RCAL/RCAS ratio during leaf aging. Our results suggest that there is a posttranscriptional mechanism regulating the RCAL/RCAS ratio, which may play as a regulator modulating photosynthetic capacity during leaf aging in rice plant. © Springer Science+Business Media B.V. 2010.