The biochemistry and regulation of senescence in chloroplasts

The biochemical events in chloroplast breakdown are described. Special attention is given to the regulation of RNA, lipid, chlorophyll, and protein degradation. A new hypothesis is presented concerning the relationship between proteolysis and the initial steps in chlorophyll breakdown. It is argued that the dismantling of the chloroplast is a highly organized process and that the concept of loss of chloroplasts by digestion in a lytic vacuole is not tenable.