The Development of Chlorophyll and Oxygen-evolving Power in Etiolated Barley Leaves When Illuminated.

Abstract

The development of chlorophyll and of 02-evolving power was followed simultaneously in etiolated barley leaves that had been illuminated under various conditions. The pigments, protochlorophyll and chlorophyll, were estimated spectrophotometrically and the O2 evolved was determined by means of a phosphorescence-quenching method. The transformation of protochlorophyll to chlorophyll a took place in an anaerobic atmosphere. It was not accompanied by the evolution of oxygen. Although the etiolated leaves that had been irradiated in air for a short time possessed chlorophyll that was derived from their protochlorophyll, they lacked the power to evolve O2. If, after this irradiation, these leaves were stored in air in darkness, they acquired a small capacity for oxygen production. This capacity was greatly augmented by a subsequent brief irradiation. Chlorophyll b was not necessary for O2 evolution.