Development of Chlorophyll and Hill Activity

A sensitive luminometer is used to measure directly the low rates of oxygen evolution during greening of etiolated barley (Hordeum vulgare L. var. Wong) leaves. Oxygen evolution is measured in leaf segments infiltrated with p-benzoquinone. When illuminated, these leaves do not produce significant amounts of oxygen until the end of the lag phase of chlorophyll synthesis. Chlorophyll is increased by feeding delta-aminolevulinic acid to leaves in the lag phase, but this does not cause an earlier appearance of photosynthesis. Chloramphenicol, and to a lesser extent cycloheximide, when fed to leaves together with delta-aminolevulinic acid, strongly inhibit the development of oxygen evolution in the light while only slightly inhibiting chlorophyll synthesis. The ability to evolve oxygen develops to only a slight extent in darkness, even in the presence of high levels of chlorophyll.We conclude that the development of photosystem II is limited by the synthesis of proteins in both the cytoplasm and the plastid, not by chlorophyll synthesis. Prolonged illumination is necessary for the development of oxygen evolution.