Ammonium ion salvage by glutamate dehydrogenase during defence response in maize

Document Type

Article

Publication Title

Phytochemistry

Abstract

When phytochemical defence response was elicited by treatment of maize with chitosan, the binomial isoenzymes of L-glutamate dehydrogenase (GDH, EC 1.4.1.2) isomerized. The amination electrode potential of the GDH charge isomers decreased by 10 mV in the chitosan-treated maize. GDH isomerization and amination are therefore spontaneous reactions. The free L-Glu and L-Gln were 3.84 μmol, respectively, per 10 g of the chitosan-treated maize. The amination activities of GDH showed that the 10 mV decrease in electrode potential accounted fully for the 3.84 μmol free L-Glu content of the chitosan-treated maize. Therefore the binomial GDH synthesized all the L- Glu, thereby salvaging at least 51% of the NH4/+ liberated during phytochemical defence response, while glutamine synthetase salvaged the remaining NH4/+. The chitosan-elicited isomerization of maize GDH and the accompanying 10 mV decrease in electrode potential widened the plant-pathogen amination energy barrier, thereby minimizing the amount NH4/+ the pathogen can absorb from the plant.

First Page

1491

Last Page

1498

DOI

10.1016/0031-9422(96)00169-0

Publication Date

1-1-1996

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