Abstract
Both water-soluble oxalic acid and water-insoluble calcium oxalate are usually found in spinach leaves. In this study, spinach was cultivated in a standard solution culture containing 0.67, 25, 50 ppm CaCl2. The plant weight and height and oxalate contents per plant and per unit weight were determined during the growing cycle. The activities of enzymes related to the biogenesis and degradation of oxalates in the leaves were compared during the growing season.
1. The increase in the weight of the spinach was proportional to the amount of Ca in solution (Fig. 2).
2. The amount of oxalate accumulated by the plant was a function of the Ca solution in the nutrient culture; a large fraction of the oxalate was in the insoluble form (Fig. 3).
3. A small amount of oxalate was exuded by the roots into the external medium. These results suggest that the formation of the water-insoluble Ca oxalate is a defense mechanism to protect the plant from a harmful buildup of soluble oxalic acid.
4. That biogenetic oxalate-enzymes, e. g., glyoxylate oxidase and oxaloacetase, and an oxalate degrading enzyme, oxalate decarboxylase, are present in spinach leaves was confirmed.
Oxalate might be biosynthesized and degraded by the action of these enzymes; the accumulation of oxalate in the plant tissues is attributed to the shift in equilibrium in favor of biosynthesis rather than degradation.
