Practice question

Plastid diversity reflects differentiation of proplastids in meristems according to tissue identity and developmental signals regulated by light, hormones and transcription factors. Elaioplasts are specialized non-photosynthetic leucoplasts lacking chlorophyll that function in lipid storage and metabolism crucial for reproduction. They are abundant in oil seeds like Brassica, citrus exocarp oil glands, and anther tapetum where lipid reserves for pollen coat tryphine formation and pollinator attraction are needed. Ultrastructurally they contain numerous electron-dense plastoglobuli and oil droplets bounded by single inner envelope, with few internal thylakoids and extensive physical connections to endoplasmic reticulum for fatty acid trafficking via touching domains. They possess complete enzymes for fatty acid synthesis, including acetyl-CoA carboxylase, fatty acid synthase complex, and stearoyl-ACP desaturase, converting imported photosynthate like sucrose-derived pyruvate into triacylglycerols and sterol esters stored as osmiophilic globules. In contrast amyloplasts accumulate starch via ADP-glucose pyrophosphorylase, proteinoplasts store proteins in crystalline protein bodies, and chromoplasts accumulate carotenoids for coloration, illustrating functional specialization supporting plant physiology.