PEP-carboxylase activity during ammonium-assimilation in wheat plants

Arnozis, P.A.; Barneix, A.J.

PEP-carboxylase activity during ammonium-assimilation in wheat plants

1989

Arnozis, P.A. | Barneix, A.J.

When 14-day old wheat plants were transferred from a medium containing nitrate as the sole N-source to one containing ammonium, the root NH4+-concentration increased rapidly. This was followed by increases in root phosphoenol pyruvate carboxilase (PEP-carboxylase) activity, concentration of glutamine, and total free amino acids. Eventually the PEP-carboxylase activity reached a plateau and free-NH4 concentration increased thereafter. Similar plants transferred from NO3 to a mixed N-source (NH4+ + NO3-) also showed an increase in root PEP-carboxylase activity. The enhancement was slower but reached the same final value as for the plants transferred to NH4+-only. The concentrations of glutamine and free amino acids increased, but to a smaller extent than in the plants transferred to all ammonium. In shoots the treatments produced no detectable changes in PEP-carboxylase activity. It is concluded that high PEP-carboxylase activity in roots helps to prevent accumulation of ammonium to toxic levels.

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