Visualization of Rubisco-Containing Bodies Derived from Chloroplasts in Living Cells of Arabidopsis

During senescence and times of stress, plants can mobilize needed nitrogen from chloroplasts in leaves to other organs. Much of the total leaf nitrogen is allocated to the most abundant plant protein, ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco). Previously by immunoelectron microscopy (IEM), we demonstrated that Rubisco is released from the chloroplast into Rubisco-containing bodies (RCBs) in naturally senescent leaves (Chiba et al. 2003). In this study, we visualized RCBs in living cells of transgenic Arabidopsis plants containing stroma-targeted green fluorescent protein (GFP). When leaves of transgenic Arabidopsis plants were incubated under starvation conditions with a vacuolar-ATPase inhibitor, spherical bodies exhibiting GFP fluorescence without chlorophyll fluorescence were observed. Spherical bodies were not observed when leaves were provided with a sugar and nutrient solution. IEM of concanamycin-A-treated leaves with anti-Rubisco antibodies confirmed the existence of RCBs in the vacuolar compartment. These results suggest the hypothesis that stromal proteins can be mobilized to the vacuole via RCBs by possibly autophagy for the degradation.