Introduction

Abstract

The green plant cells are distinguished from the cells of other eukaryotic organisms primarily by the presence of plastids in them. Chloroplast is one of the plastids that is photosynthetically active and finds its origin from a small and colorless proplastid (Sundqvist and Dahlin, 1997). The proplastids, however, may develop into various types of plastid with significant diversity in their size, ultrastructure, biochemical activities, and metabolic functions (Lichtenthaler, 1968; Mullet, 1988; Hudak, 1997). Although the role of plastid centers around photosynthetic carbon assimilation, portions of several metabolic pathways including lipid biosynthesis and amino acid metabolism pass through the plastids (Galili,1995; Ohlrogge and Browse,1995). Plastids are also known to generate lipid derived signaling molecules and participate partially in the synthesis of some phytohormones (Joyard et al., 1998). The literature on the diversity of structure and function of plastids is vast and the scope of in-depth description of their forms and physiology in this book is limited.