The influence of calcium deficiency on the translocation of photosynthetically fixed ¹⁴C in soybeans

Summary

Soybean (Glycine max (L.) Merr.) plants were grown at two levels of Ca (0.05 and 2.5 mM Ca) with and without an inorganic source of N in a growth chamber and in the greenhouse. The fourth leaf from the top of the plant was labeled with ¹⁴C, and the distribution of ¹⁴C was measured 24 hours after labeling. The translocation of ¹⁴C out of the labeled leaf was decreased at the low Ca level in both experiments. This decrease occurred before there were any visual Ca deficiency symptoms and before the low Ca level had any effect on dry weight accumulation. The effect of the low Ca level on translocation was the same for plants exposed to an inorganic N source and those that were nodulated. The reduced rate of translocation from the labeled leaf had no measurable effect on the nodule activity as measured by the acetylene reduction method. The data demonstrate the importance of an adequate supply of Ca to the soybean plant for maximum translocation of carbohydrates from the leaves.