EFFECT OF SHORT-CHAIN FATTY ACIDS ON RESPIRATION OF WHEAT STEM RUST UREDOSPORES

Fatty acids added to a suspension of wheat stem rust uredospores (Puccinia graminis var. tritici, race 15B) stimulate respiration. When compared on the basis of equal molar concentration, the utilization of oxygen by spores from wheat grown in the field or in the greenhouse is stimulated by short-chain fatty acids as follows: acetate < propionate < butyrate < valerate. The order for butyrate and valerate is reversed with spores from plants grown under artificial light. Radiotracer experiments indicate that the amount of respired carbon dioxide derived from the carboxyl carbon of the fatty acid added increases markedly with increase in chain length. The addition of exogenous acetate stimulated conversion of spore carbon to carbon dioxide, whereas valerate replaces, in part, spore material as a source of respiratory carbon. Valerate-1-C14 is almost 4 times as effective as acetate-1-C14 for labelling spore material, but the ratio of carbon-14 respired to that incorporated is 2.6 for valerate-1-C14 as compared with 1.5 for acetate-1-C14.