Figure 1: Diversity of Plastid Forms and their Interconversions

Plastids exist in different forms, and the identity and abundance of each are controlled by developmental and environmental cues. Different types interconvert (see the arrows) following reorganization of the organellar proteome, a process that is controlled by the differentially regulated import of nucleus-encoded proteins. Chloroplasts are photosynthetic plastids, amyloplasts are starch-storing plastids, chromoplasts are carotenoid pigment-accumulating plastids, and proplastids are undifferentiated plastids that can differentiate into the different types of plastids. Etioplasts are chloroplast progenitors that form in darkness and accumulate chlorophyll precursors (in paracrystalline membranous structures called prolamellar bodies (PLB)) that are ready for rapid differentiation upon illumination. Elaioplasts store lipids in lipid droplets known as plastoglobules and exist, for example, in tapetal cells during pollen development. Gerontoplasts form during senescence, owing to resource recycling through the disassembly of the photosynthetic machinery and autophagy. Taken from Nat. Rev. Mol. Cell Biol., 2013, 14: 787-802.