Chromoplast Development in Daffodil Coronae during Anthesis

Summary The development of membraneous chromoplasts in growing coronae of the daffodil has been investigated fine-structurally and biochemically. Three stages have been selected: Flower buds with greenish prochromoplasts, opening flowers, and open flowers with fully-grown chromoplasts. As there are no cell divisions in these stages, the growth of the coronae is solely due to cell enlargement. The doubling of the projection area of the cells is accompanied by a doubling of chromoplast number per cell. Transition of prochromoplasts to chromoplasts is marked by thylakoid and chlorophyll degradation. Concomitantly, there is a rapid increase in plastidspecific polar lipids and carotenoids, and chromoplast-specific proteins begin to accumulate. However, in the course of these changes, the number of plastid ribosomes diminishes. Whereas their portion among total cellular ribosomes amounts to 10 % in flower buds, plastid ribosomes cannot be detected in coronae with fully developed chromoplasts. Further, although plastid polysomes are present in all developmental stages in green leaves, no plastid polysomes could be detected in coronae of opening or open flowers. Accordingly, no protein synthesis can occur in chromoplasts of the daffodil, contrary to other types of plastids which possess polysomes active in translation. On the basis of these results it is to be supposed that chromoplast-specific proteins in general are coded for in the nucleus and must be imported into developing chromoplasts from the cytoplasm.