Variation of plastid types in spinach

Summary During growth in the light the plastids of cultured leaf discs of spinach divide, increase in size, and differentiate in a similar manner to those in intact leaves. By contrast when l'eaf discs are grown in the dark prolamellar bodies begin to develop in partially differentiated chloroplasts within 2 hours. After 7 days growth in the dark the plastids contain many vesicles which appear to arise from swelling of thylakoids. These vesicles often contain large crystals. When dark grown discs are illuminated they regreen and fully differentiated chloroplasts are reformed.Proplastids are found in the stem apex of whole plants; these develop into the partially differentiated chloroplasts of young leaves, which divide and increase in size to form the fully differentiated chloroplasts of mature leaves. The cotyledons of dormant seeds contain proplastids; these develop into amyloplasts during germination and after exposure to white light differentiate into chloroplasts.