Fragmentation of the large subunit of Rubisco by reactive oxygen species occurs in cucumber leaf discs chilled in the light

Abstract

The production of reactive oxygen species (ROS) in chloroplasts is stimulated during leaf senescence and under stress conditions.It is suggested that ROS act as a trigger of protein degradation.Actually,direct degradation of the large subunit of Rubisco by ROS has previously been shown in vitro.However,it is unknown whether ROS cause the fragmentation of Rubsco-LSU in vivo.In this study,we examined whether the fragmentation of the LSU by ROS occurs in vivo. When leaf discs of a chilling sensitive plant ,cucumber, were incubated in the light at 4^oC,five fragments of the LSU were time-dependently appeared.The fragmentation was inhibited by the ROS scavengers,n-propyl gallate and tiron.While FeSO₄ stimulated the fragmentation,iron specific chelator,deferoxamine,prevented it.Furthermore,when the purified cucumber Rubisco was exposed to the hydroxyl radical-generating system,the fragments produced were identical to those of the light-chilling discs in molecular weights and isoelectric points. These results suggest that the direct fragmentation of LSU by ROS occurs in vivo.