Nitrate levels and enzyme activity in sorghum leaves were studied as they grew. Nitrate reductase activity increased early on, peaked at full leaf size, then decreased as leaves matured. Nitrate content followed this pattern. Glutamine synthetase activity rose at first, then stayed steady until leaves aged. Leaves from nitrate-fed plants had low nitrate reductase activity in the dark, but it shot up when exposed to light. Glutamine synthetase activity was already high in these leaves and increased slightly during greening. The enzyme was not affected by cyanide and was boosted by cysteine. Overall, glutamine synthetase activity remained high throughout leaf development and greening, showing it helps convert nitrate into amino acids and ammonia.