Studies of Chloroplast Development in Euglena. VII. Fine Structure of the Developing Plastid

Abstract

Rep-resentative electron micrographs of Euglena cells undergoing chloro-plast development are presented. Dark-grown cells contain proplastids about 1[mu] in diameter which develop into the elongated chloroplasts characteristic of light-grown cells when exposed to optimal intensities of 100 ft-c under non-dividing conditions. The lengths of the developing plastids, widths, number of free discs and number of lamellae were measured and the kinetics of these parameters during development are presented. Cells in which chloroplast development has been limited by low light intensities have also been studied and exhibit various types of plastid abnormalities. The normal developmental sequence at 100 ft-c correlates well with physiological parameters such as pigment formation and photosynthetic oxygen evolution and carbon dioxide fixation. There is a strong correlation between the rate of lamellar formation from 14 to 72 hours of development and the rate at which the physiological parameters increase. Chloroplast development in Euglena appears to differ from that described for higher plants since discs, rather than vesicles, are invaginated from the inner proplastid membrane, and there is no prolamellar body. The sequential nature of development found in Euglena appears to be unique and permits a quan-titation of physiological and developmental events not possible before.