Abstract
During leaf senescence, the degradation of chloroplast proteins represents one of the nitrogen translocation mechanisms. Rubisco accounts for 12-35% of total leaf nitrogen and is the main source for nitrogen translocation. In wheat and barley, Rubisco content decreases much faster than the number of chloroplast. Therefore, it is thought that Rubisco is either degraded within chloroplasts, or by autophagy-like transport pathway via RCBs (Rubisco-containing bodies), or both. In this study, we analyzed changes in Rubisco, leaf nitrogen, chlorophyll contents and chloroplasts number during leaf senescence in wild-type Arabidopsis and autophagy defected mutant, Atatg4a4b-1.
The amount of Rubisco, leaf nitrogen and chlorophyll decreased equally in both Atatg4a4b-1 and in the wild-type, until 80% of Rubisco was decreased. Subsequently, Atatg4a4b-1 senesced faster than wild-type. However, the chloroplast number remained stable until the majority of Rubisco was degraded. As the result, Atatg4a4b-1 mutant retained the equivalent potential to degrade chloroplast proteins to wild-type.
