INFLUENCE OF IRRADIANCE ON ENZYMES OF SULFATE AND NITRATE ASSIMILATION PATHWAYS IN MAIZE LEAVES

The activities of nitrate reductase (EC 1.6.6.1) (NR), glutamine synth etase (EC 6.3.1.2) (GS), glutamate dehydrogenase (EC 1.4.1.2) (GDH), A TP-sulphurylase (EC 2.7.7.4) (ATP-s) and O-acetylserine sulphydrylase (EC 4.2.99.8) (OAS-s) and N and S status were determined in the leaves of 10 d old Zen mays L. plants grown at low and high irradiance. All the enzyme activities were increased in leaves grown in high light, AT P-s showing the highest increment. Nitrate reductase was slightly affe cted, but the activity assayed in the presence of Mg2+ indicated an in creased percentage of activation in leaves of plants grown at high irr adiance. Total N and sulphate content were increased under high light, whereas total S and nitrate were decreased.