Ammonium Production in Cultures of Bipolaris maydis Race T: Evidence for Involvement of Asparaginase and NADP- and NAD-Glutamate Dehydrogenases
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Citation:The Ohio Journal of Science. v86, n5 (December, 1986), 186-189
When Bipolaris maydis race T was incubated in a liquid medium (2 g/l glucose, 4 g/l Lasparagine, and mineral salts), ammonium and pH failed to increase after 48 h, but both increased after 72 h from 0.0 to 21.8 /mioles NH4 +/ml, and from pH 5.8 to 7.9. Also at 72 h, glucose was no longer detected. When the activities of NADP-glutamate dehydrogenase (NADP-gdh), NAD-glutamate dehydrogenase (NADgdh) and L-asparaginase were assayed, NADP-gdh was high at 48 h and low at 72 h, and NAD-gdh was low at 48 h and high at 72 h. There were no differences in asparaginase activity after 48 or 72 h. To test the effects of cycloheximide on enzyme activity and ammonium accumulation, filter-sterilized (pore size 0.45 fxm) cycloheximide was added at a rate of 10 /*g/ml at 48 h and the assays were made at 72 and 96 h. Addition of cycloheximide inhibited dry weight increase, stopped removal of glucose from the culture medium, prevented pH increase, and blocked the transition from high NADP-gdh to high NAD-gdh activity. Only 10.0 /xmoles/ml ammonium accumulated in cycloheximide-treated cultures in contrast to 21.8 ^moles/ml in the control, and asparaginase activity was unaffected. Thus, ammonium accumulation following glucose depletion may be related to the reduction of ammonium assimilated via NADP-gdh and the production of ammonium via asparaginase and NAD-gdh.
Author Institution: Department of Plant Pathology, The Ohio State University
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