Ultrastructural development of plastids in the epidermis and starch layer of glossy Ranunculus petals

Abstract

The differentiation of chromoplasts and amyloplasts has been followed in developing petals of Ranunculus acris, R. ficaria and R. repens from small bud stages through anthesis. These are typical of Ranunculus species with glossy yellow petals. The plastids in the adaxial epidermis of the glossy part develop many globules which enlarge and coalesce with the eventual complete breakdown of plastid structure. At anthesis only a few cytoplasmic remnants remain in the dispersed pigment in these cells which partially collapse with folding of the anticlinal walls. In the non-glossy proximal part of the petal the adaxial epidermal cells have more convex outer walls and the chromoplast development does not progress beyond a stage found in the glossy region just before the petal tips emerge from the bud: they have large peripheral globules with irregular tubular lamellae between them and in the central stroma. In the abaxial epidermis the plastids produce small globules and retain some grana; some have small starch grains and differ little from the plastids in the mesophyll. The starch layer beneath the adaxial epidermis in the glossy region is formed from a single embryonic cell layer. Amyloplasts differentiate rapidly in these cells and all plastid structure has disappeared before the flower bud opens leaving the sloping palisade cells packed with starch grains. © 1986 Annals of Botany Company.