Gene Expression and Accumulation of Rubisco in Bundle Sheath and Mesophyll Cells during Leaf Development and Senescence in Rice, a C3 Plant

Abstract

Gene expression of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) large subunit (rbcL) and small subunit (rbcS) in bundle sheath and mesophyll cells of rice, a C3 plant, was examined during leaf development and senescence by in situ hybridization. Localization of Rubisco protein in both cells was also examined by immuno-electron microscopy. Gene expression and accumulation of Rubisco were related with the chlorophyll fluorescence parameters. The chlorophyll fluorescence parameters, such as Fv/Fm and Φpsii, gradually increased during leaf development with the increase in the accumulation of Rubisco. However, the chlorophyll fluorescence parameters decreased earlier than the Rubisco content during leaf senescence. The expression of rbcS decreased earlier in bundle sheath cells than in mesophyll cells during leaf development, whereas the expression of rbcL in both cells was retained during leaf development and decreased during leaf senescence. On the other hand, Rubisco content of bundle sheath and mesophyll cells increased during leaf development and decreased during leaf senescence. Rubisco was retained even after the disappearance of the expression of rbcS and rbcL detectable by in situ hybridization. The present results suggest that the expression pattern of rbcS in bundle sheath cells was somewhat different from that in mesophyll cells, but this difference was not reflected in Rubisco content.