Ricerche Sulla Morfogenesi Dei Plastidi Clorofilliani

Abstract

Studies on the morphogenesis of the chloroplasts. ii: effects of the red and far-red lights on the evolution of the dark grown plastids. — Etiolated, twelve days old Bean seedlings have been exposed for 12 hours to red, far-red and white lights of different intensities. White light induces in the plastids the formation of a system of grana and stroma-lamellae whose development is enhanced by higher light intensities. Red light, conversely, causes the resolution of the vesicular body into several vesicles, which appear either scattered or lined up in rows. No modification of the plastidial structures could be observed in the plants exposed to the far-red light, besides a slight enhancement of the lamellae arranged concentrically around the vesicular centers. The seedlings exposed to white light synthetize chlorophylls a and b in amounts proportional to light intensity; under red light the amounts of photopigments synthetized closely approach those observed upon illumination with white light of maximum intensity, whilst with far-red light only very small amounts are formed. These observations suggest that the synthesis of chlorophyll in the plastid is not necessarily connected with the formation of a regular system of grana and stroma lamellae; besides that, it can be observed that red light, which induces the formation of vesicles, cannot induce a more differentiated structure, even after a very long exposure. The conservation of the crystalline structure of the vesicular body, in the plants exposed to far-red light, suggests that the high-energy reaction, which has been realized in the course of these experiments, does not cause any effect neither on the chlorophyll synthesis, nor on the morphogenesis of the plastidial structures.