Anoxic Seed Germination of<i>Erythrina caffra</i>: Ethanol Fermentation and Response to Metabolic Inhibitors

Abstract

Erythrina caffra seeds were shown to be true anaerobic germinators. They exhibit a Pasteur effect, high alcohol dehydrogenase activity and produce high levels of ethanol under anoxia, in which situation germination starts to be suppressed by as little as 0.1% externally applied ethanol. Toxic levels of ethanol production appear to be prevented by a decrease in the rate of ethanol accumulation. Carbon monoxide does not inhibit germination. Cyanide, SHAM, iodoacetate, pyrazole, and 4-methylpyrazole are more inhibitory to anoxic than aerobic germination whereas azide, arsenate, and fluoride inhibit both. Azide, pyrazole, 4-methylpyrazole and a low concentration of cyanide and SHAM tend to stimulate ethanol production in air. At 10 mol m−3, 4-methylpyrazole stimulates anaerobic ethanol production. At higher concentrations this compound and all other inhibitors used suppress anaerobic ethanol production initially. Inhibition of ethanol production by 10 mol m−3 cyanide is paralleled by an accumulation of acetaldehyde. Azide and cyanide appear to exert their inhibitory effect at different loci.