Effects of calcium on the photosynthesis of intact leaves and isolated chloroplasts of sugar beets.

Effects of calcium on photosynthesis in sugar beets (Beta vulgaris L. cv. F58-554H1) were studied by inducing calcium deficiency and determining changes in CO(2) uptake by attached leaves, electron transport, and photophosphorylation by isolated chloroplasts, and CO(2) assimilation by ribulose diphosphate carboxylase extracts. Calcium deficiency had no significant effect on leaf CO(2) uptake, photoreduction of ferricyanide, cyclic or noncyclic ATP formation of isolated chloroplasts, or on ribulose diphosphate carboxylase CO(2) assimilation, when the rates were expressed per unit chlorophyll. When expressed per unit leaf area CO(2) uptake increased by about 15% in low calcium leaves. The most noticeable effect of calcium deficiency was reduction in leaf area: low calcium had no effect on dark respiratory CO(2) evolution, on leaf diffusion resistance, or on mesophyll resistance to CO(2). We concluded that only small amounts of calcium are required for normal photosynthetic activity of sugar beet leaves.