Plastid Development in Leaves during Growth and Senescence

Abstract

The overview provides basic information on the appearance and biosynthesis of thylakoids and osmiophilic plastoglobuli and their association with chloroplast development and senescence. The light-induced formation of sun chloroplasts at high irradiation with a different thylakoid arrangement, grana stacking and plastoglobuli content as compared to shade chloroplasts at low irradiation is reviewed. During the light-induced biosynthesis of thylakoids from etioplasts of dark-grown seedlings the osmiophilic plastoglobuli disappear. Young chloroplasts are actually free of osmiophilic plastoglobuli. With increasing age of chloroplasts osmiophilic plastoglobuli appear again and are either fairly frequent at a small diameter or show up in a lower number with rather large size. In senescing chloroplasts and in their fi nal form, gerontoplasts, thylakoids and chlorophylls are successively broken down with formation of large plastoglobuli. In addition to the plastoglobuli of chloroplasts, the occurrence and role of plastoglobuli during the development of chlorophyll-free plastid forms, such as proplastids, leucoplasts, and chromoplasts are presented. The main function of plastoglobuli as stores for plastidic lipids, such as plastoquinone-9, plastoquinol-9 and a -tocopherol and in certain plastid stages also other lipids is discussed. Recent observations suggest that plastoglobuli contain on their outer surface certain functional chloroplast proteins participating in biosynthesis and the channeling of lipid molecules.