Effects of fusaric acid on respiration in maize root mitochondria

The effects of fusaric acid, a phytotoxin produced byFusarium pathogens, on the metabolism of isolated maize root mitochondria and on maize seed germination and seedling growth were investigated. The phytotoxin inhibited basal and coupled respiration when succinate and α-ketoglutarate were the substrates. Coupled respiration dependent on NADH was inhibited, but basal respiration was not. Consistently, succinate cytochromec oxidoreductase activity was decreased whereas NADH cytochromec oxidoreductase was not affected. The ATPase activities of carbonyl cyanide p-trifluoro-methoxyphenyl hydrazone stimulated mitochondria and of freeze-thawing disrupted mitochondria were inhibited. These results indicate that the phytotoxin impairs the respiratory activity of maize mitochondria by at least three mechanisms: (1) it inhibits the flow of electrons between succinate dehydrogenase and coenzyme Q, (2) it inhibits ATPase/ATP-synthase activity and (3) it possibly inhibits α-ketoglutarate dehydrogenase. Seed germination and seedling growth were also affected by fusaric acid with the most pronounced effect on root development. These effects can possibly contribute to the diseases ofFusarium- infected plants