Ammonia Production and Assimilation in Glutamate Synthase Mutants of Arabidopsis thaliana1
AUTOR(ES)
Morris, Paul F.
RESUMO
Ammonia production and assimilation1 were examined in photorespiratory mutants of Arabidopsis thaliana L. lacking ferredoxin-dependent glutamate synthase (Fd-GluS) activity. Although photosynthesis was rapidly inhibited in these mutants in normal air, NH4+ continued to accumulate. The accumulation of NH4+ was also seen after an initial lag of 30 minutes in 2% O2, 350 microliters per liter of CO2 and after 90 minutes in 2% O2, 900 microliters per liter of CO2. The accumulation of NH4+ in normal air and low O2 was also associated with an increase in the total pool of amino acid-N and glutamine, and a decrease in the pools of glutamate, aspartate, alanine, and serine. Upon return to dark conditions, or to 21% O2, 1% CO2 in the light, the NH4+ which had accumulated in the leaves was reassimilated into amino acids. The addition of methionine sulfoximine (MSO) resulted in higher accumulations of NH4+ in glutamate synthase mutants and prevented the reassimilation of NH4+ upon return to the dark. The addition of MSO also resulted in the accumulation of NH4+ in glutamate synthase mutants in the light and in 21% O2, 1% CO2. These results indicate that glutamine synthetase is essential for the reassimilation of photorespiratory NH4+ and for primary N assimilation in the leaves and strongly suggest that glutamate dehydrogenase plays only a minimal role in the assimilation of ammonia. Levels of NADH-dependent glutamate synthase (NADH-GluS) appear to be sufficient to account for the assimilation of NH4+ by a GS/NADH-GluS cycle.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1054715Documentos Relacionados
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