Tansley review no 92 - Chlorophyll: A symptom and a regulator of plastid development

The metabolism of chlorophylls and related tetrapyrroles directly influences, and is influenced by, the proteins and cell structures with which they are associated. During net accumulation, de-greening and at the steady state, chlorophyll and its derivatives are important elements in the post-translational regulation of the expression of genes for chloroplast proteins. At the same time, they represent potential photodynamic hazards against which green cells need to have protective mechanisms. This review deals with genetic, chemical and environmental perturbations of chlorophyll biosynthesis that impact on protein stability, membrane organization and susceptibility to photodamage. NADPH-protochlorophyllide oxidoreductase is considered in detail as a pigment-protein regulating, and regulated by, chlorophyll metabolism. The question of the extent and significance of chlorophyll turnover at the steady state is addressed, with particular emphasis on the dynamics of the photosystem II reaction centre. The pathway of chlorophyll catabolism is described, along with its interrelationship with protein mobilization in chloroplast senescence. Finally, the structural basis of pigment-protein interaction and stability is examined, and the discussion ends by expressing some general thoughts about the control of protein lifetimes in the living cell.