Changes in the activities of ferredoxin- and NADH-glutamate synthase during seedling development of peas

Ferredoxin-glutamate synthase (EC 1.4.7.1) and NADH-glutamate synthase (EC 1.4.1.14) activities in pea seedlings (Pisum sativum L., cv. Alaska) were measured during germination and the early stages of growth. Both enzymes were detected at all stages in the developing roots and shoots, but their relative activities varied according to the growth stages. In shoots of 5-d-old seedlings, the ratio of the NADH-enzyme to the ferredoxin-enzyme was 72:28. However, the ferredoxin-activity increased rapidly and in shoots of 17-d-old seedlings, the activities were in the ratio of 3:97. Similar trends in these ratio changes were observed in the roots. In both tissues, the NADH-enzyme was shown to be predominant in the immature parts. When chloroplasts prepared from mature pea leaves were incubated with [(14)C]glutamine and 2-oxoglutarate, the production of [(14)C]glutamate was found to be light dependent and was inhibited by azaserine (3 mM) and 3-(3,4-dichlorophenyl)-1-1-dimethylurea (20 μM). In contrast, considerable amounts of [(14)C]glutamate were formed by chloroplasts from young leaves even in the dark. Addition of malate or dihydroxyacetone phosphate to the reaction mixture resulted in a twofold increase of this dark- and azaserine-sensitive [(14)C]glutamate formation.