CoachPlastids are the double-membraned organelles of plant cells: chloroplasts, in which a third system of membranes, the thylakoids, stacked in grana and bathed in the stroma, carries out photosynthesis (Chapter 14); amyloplasts, which store starch; chromoplasts, which hold the pigments of fruits and petals. All derive from proplastids and, like mitochondria, contain their own circular DNA and bacterial-type ribosomes and divide by fission.
