Ammonium ion salvage by glutamate dehydrogenase during defence response in maize
When phytochemical defence response was elicited by treatment of maize with chitosan, the binomial isoenzymes of L-glutamate dehydrogenase (GDH, EC 220.127.116.11) 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.
Osuji, G., & Madu, W. (1996). Ammonium ion salvage by glutamate dehydrogenase during defence response in maize. Phytochemistry, 42 (6), 1491-1498. https://doi.org/10.1016/0031-9422(96)00169-0