Biometric Analysis of the Thylakoid System Development during Chloroplast Ontogenesis in Leaves of Two Orchids, Coelogyne cristata and Cymbidium insigne

Abstract

Biometrical analysis of membrane genesis performed on the electron micrographs of chloroplasts from leaves of two orchids, Coelogyne cristata and Cymbidium insigne has shown that the successive stages of plastid growth are accompanied by a continuous increase in the number of grana. In a consequence of progressive appearance of still new grana stacks, as well as the increment in height of the preexisting grana, the number of thylakoids in stacks is variable. However, during the whole ontogenesis of chloroplasts the low grana number (2–10 thylakoids per stack) is dominating. From the counts of the number of both the grana and stroma thylakoids it appears that the increase in their number during successive stages of chloroplast development occurs in keeping the proportion between the number of grana and stroma thylakoids, the ratio being approximately 4: 1. During the early stages of chloroplast development (between stage II and III) it was found that an intensive increase in size of chloroplasts takes place, correlated with the rapid development of their lamellar system. The increase in these processes is connected with the phase of emergence of the basal (celadon) leaf zone from the leaf-sheath.