A. Diaz et al., PHOSPHINOTHRICIN REVERTS THE AMMONIA-DEPENDENT ENHANCEMENT OF PHOSPHOENOLPYRUVATE CARBOXYLASE ACTIVITY, Journal of plant physiology, 145(1-2), 1995, pp. 11-16
The effect of ammonium assimilation on phosphoenolpyruvate carboxylase
(PEPCase) activity was investigated in detached leaves from N-limited
barley plants. The time-course induction of PEPCase was dependent on
the rate of ammonia assimilation and not on ammonia uptake or accumula
tion. Treatment of N-deprived leaves with phosphinothricin (an inhibit
or of glutamine synthetase activity) caused inhibition of ammonia assi
milation, resulting in the reversion of ammonia-dependent enhancement
of PEPCase. The results indicate that glutamine level controls phospho
enolpyruvate carboxylase activation; consequently, if glutamine synthe
sis is inhibited, PEPCase activity is not enhanced. Determination of m
alate content showed that as PEPCase activity increased in response to
increasing ammonia assimilation, there was a linear decline in the le
vel of that metabolite. We have also analyzed the in vivo effect of ma
late on ammonium-dependent activation of PEPCase. High malate uptake p
artially abolished PEPCase activation, but the induced PEPCase activit
y seems to be less sensitive to malate than the control one.