Changes in the uptake and assimilation efficiency for sulfate and nitrate in maize hybrids selected during the period 1930 through 1975

Sulfate and nitrate uptake capacity, ATP sulfurylase (ATPS) and nitrate reductase (NR) activity were determined in a set of maize hybrids representative of selection cycles carried out during the period 1930 through 1975. All the above metabolic parameters together with the grain yield were improved by the selection. The annual rate of the improvement was higher (double) for sulfate uptake than for ATPS and similar for NR and nitrate uptake. Significant correlations were evidenced between the uptake efficiency of the roots and the enzyme activity in the leaves both for sulfate and nitrate pathways, and also between the uptake and enzyme steps of nitrate and those of sulfate. This offered good evidence of a coupled genetic regulation between nitrogen and sulfur metabolism in maize.