Relationships between Oxalate and Reduced N Concentrations in Spinach Leaves

Abstract

The relationships among oxalate, reduced N, and cation concentrations in leaves were examined for 14 cultivars of spinach grown in solution culture in the spring and fall.
Spinach leaves contained oxalate, malate, succinate, citrate, tartrate, and fumarate as non-volatile organic acids; their concentrations decreased in the respective order. Concentrations of total organic acids (TOA) differed among cultivars; they were closely correlated with concentrations of oxalate.
NO₃^- concentrations in leaves were extremely low as compared with those of total N, especially in leaves of spinach cultivars in spring. The relationship between reduced N and TOA concentrations as expressed as meq-g^-1 FW was fitted a 1:1 theoretical ratio in the fall experiment. Concentrations of reduced N were a little higher relative to those of TOA in the spring, so that the slope of the curve was steeper. Nevertheless, the distribution formed a straight-line relationship (r= 0.937). Concentrations of sum of K, Na, Ca and Mg were higher than those of TOA. The correlation coefficients between the two variables for the cultivars examined were highly significant.
The data indicate that oxalate is synthesized in response to NO3- reduction and is not metabolized in spinach leaves.