BLUE‐LIGHT INDUCED DEVELOPMENT OF CHLOROPLASTS IN ISOLATED SEEDLING ROOTS. PREFERENTIAL SYNTHESIS OF CHLOROPLAST RIBOSOMAL RNA SPECIES

Abstract

AbstractExcised roots of pea seedlings (Pisum sativum var. “Alaska”) cultured in a synthetic medium under sterile conditions exhibit differentiation of functional chloroplasts from leucoplasts when irradiated with blue light (350–550 nm). This transition is a relatively slow process; nevertheless, the chloroplasts formed in blue light compare very well to leaf chloroplasts as far as microstructure and photosyn‐thetic activities are concerned.Apparently certain activities of the apical meristem are mandatory in bringing about a transition from leucoplasts to chloroplasts in blue light. After short‐time labelling with [jH]uridine the synthesis of plastid ribosomal RNA (rRNA) was studied either during irradiation with blue and red light (600–700 nm), respectively, or in darkness. Polyacrylamide gel electrophoresis revealed that in blue light the synthesis of specific chloroplast rRNA species with molecular weights of 1.1 × 106 and 0.56 × 106 daltons is markedly stimulated. In contrast, in dark cultured roots these RNA species were synthesized to a limited extent only whereas the cytoplasmic rRNA species of 1.3 × 106 and 0.7 × 106 daltons molecular weight were preferentially formed. The same holds true for roots irradiated with red light.