Inhibition of the development of Schizophyllum commune germlings by the ammonium ion

Ammonium ions at a concentration of 1 mm completely inhibit the growth and further development of 12–15 hr germlings of Schizophyllum commune. The NH4+, inhibition of germling growth is reversed by acetate and pyruvate, but it is reversed more effectively by TCA intermediates. Glucose, is not effective in reversing the ammonium inhibition. From these data it is apparent that functional TCA enzymes are present in the germling stage and that the mechanisms for incorporating acetate and pyruvate into the TCA cycle are also operative. There may be, however, an impaired glycolytic pathway, and, as a consequence, no intermediates are supplied to the TCA cycle, making the germlings sensitive to a disruption in the TCA cycle. The possible mode of action of ammonium ions is the activation of NADP-glutamate dehydrogenase, the subsequent enhancement of glutamic acid biosynthesis, and the final depletion of TCA intermediates.