Studies on the Manganese of the Chloroplast

Abstract

Manganese deficiency of green plants is known to affect preferentially the activity of the oxygen evolving system in the photosynthetic apparatus. The time needed to reactivate photosynthesis in Mndeficient algae was shown to vary with each culture, and is often very short when Mn is added not before illumination but during the light period. The plain incorporation of 54Mn into deficient algae as distinguished from reactivation was barely affected by light, yet was inhibited by uncouplers of phosphorylation. Higher plants responded to manganese deficiency either by adjusting the number of chloroplasts per cell to the limited Mn supply, or by forming disorganized chloroplasts with low chlorophyll content. These 2 types of responses produced chlorotic plants which had either a few photosynthetically active or many disabled chloroplasts. Photosystem I mediated photophos-phorylation turned out to be much more sensitive to manganese deficiency than the system 1 dependent photoreduction of NADP+.