Chlorophyll: a symptom and a regulator of plastid development

Abstract

SUMMARYThe 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. CONTENTS Summary 163 I. Introduction 164 II. Chlorophyll and related tetrapyrroles 164 III. Chlorophyll‐protein complexes 164 IV. Chlorophyll biosynthesis 166 V. NADPH‐protochlorophyllide oxidoreductase 168 VI. Assembling chlorophyll‐proteins 171 VII. Chlorophyll turnover at the steady state 172 VIII. The plastid family tree 173 IX. The pathway of chlorophyll catabolism 173 X. Chlorophyll and associated proteins in senescence 175 XI. How does chlorophyll stabilize associated proteins ? 176 XII. Conclusion 177 Acknowledgements 177