Effects of different nitrogen sources on glutamine synthetase and ferredoxin dependent glutamate synthase activities and on free amino acid composition in radish plants

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Abstract
Activities of ammonia-assimilating enzymes in radish (Raphanus sativus) leaves were measured to obtain information on the stimulation of NH4 + assimilation by simultaneous NO3 − supply. The leaves of the plants which received 5 mM NH4 + plus 1 mM NO3 − (5:1 mix-N) exhibited higher activities of glutamine synthetase than those of the NH4 +-fed plants. Activities of ferredoxin-dependent glutamate synthase were higher in the leaves of the 5:1 mix-N-fed plants than in those of the NH4 +-fed plants after 4 days of water culture. The leaves of the plants fed 5:1 mix-N contained larger amounts of aspartic acid and glutamic acid than those of the NH4 +-fed plants.