EFFECT OF PHOSPHINOTHRICIN ON NITROGEN-METABOLISM OF TRICHODERMA SPECIES AND ITS IMPLICATIONS FOR THEIR CONTROL OF PHYTOPATHOGENIC FUNGI

The antagonistic control of the phytopathogen Fusarium oxysporum by Tr ichoderma species is impaired in the presence of phosphinothricin, a m icrobial toxin commercialized for chemical weed control under trade na mes Basta, Ignite, and Herbiace. The influence of phosphinothricin on growth parameters and nitrogen metabolism in nine strains of Trichoder ma and a closely related fungus Nectria ochroleuca was investigated. T he presence of 1 mM phosphinothricin was lethal to the Trichoderma ana morph of Hypocrea gelatinosa and almost equally inhibitory to Trichode rma polysporum. In other species it caused marked reductions in the hy phal protein content, accompanied by lower biomass yields in all excep t N. ochroleuca. Under normal growth conditions, these rapidly growing fungi maintain highly active levels of the two key enzymes of ammoniu m assimilation, glutamine synthetase, and NADPH-dependent glutamate de hydrogenase. Phosphinothricin, by causing an inhibition in glutamine s ynthetase activity, diminishes the enzymic potential for the combined operation of these two alternative pathways. The level of NADPH-glutam ate dehydrogenase activity was exceptionally high in N. ochroleuca, an d although declining in the presence of phosphinothricin, remained muc h higher than those in nine strains of Trichoderma. The levels of NADP H-glutamate dehydrogenase in T. harzianum, T. citrinoviride, and T. vi ride were higher in the presence than in the absence of phosphinothric in. In the presence of phosphinothricin, the levels of both aspartate aminotransferase and alanine aminotransferase activities were stimulat ed in T. harzianum, T. atroviride, T. citrinoviride, and T. viride and that of alanine aminotransferase in T. koningii. Trichoderma harzianu m and T. atroviride contain single anionic molecular forms of glutamin e synthetase, NADPH-glutamate dehydrogenase, and alanine aminotransfer ase and two isoforms of aspartate aminotransferase both in the presenc e and in the absence of phosphinothricin. (C) 1995 Academic Press, Inc .