RNA synthesis during chloroplast development in Euglena gracilis

Abstract

Changes in chloroplast and cytoplasmic RNA were measured during chloroplast development in Euglena gracilis over a 3-day period. The cells were grown in the dark and then illuminated by 1500 lx of white light at a cell density which was sufficiently high to prevent any cell division in illuminated cultures. Light stimulated incorporation of 14C-orotic acid into both chloroplast and cytoplasmic RNA. The most rapid rate of light-dependent incorporation occurred during the first 8 hr of illumination and before the main period of chlorophyll synthesis. The specific activity of chloroplast RNA was higher than that of cytoplasmic RNA, particularly during the first 24 hr of illumination. By 32 hr the rate of incorporation into total cell RNA had decreased to that of dark control cells. White there was no significant change in the amount of RNA per cell during chloroplast development, the amount of chloroplast RNA increased to a maximum of 7 per cent of the total cellular RNA by 16 hr. In growing autotrophic cultures, or in cultures in which chloroplast development was followed at low cell densities (3 × 10 6 cells per ml), chloroplast RNA accounted for about one-fifth of the total cellular RNA.