Herbicidal activity of dealanyl ascamycin, a nucleoside antibiotic

A strongly phytotoxic activity was detected on screening culture broths of soil streptomyces strains for herbicidal compounds. The active principle was isolated and identified as dealanylascamycin, an already described nucleoside antibiotic affecting bacterial protein synthesis. This compound strongly inhibited growth and development of both plant seedlings in Petri dishes and whole plants in pre- and postemergence tests, as well as the growth of cultured plant cells. Monocot and dicot species were similarly affected. The inhibition was more pronounced on roots than on shoots, while the germination rate was only slightly reduced. A preliminary investigation on the herbicidal mode of action of dealanylascamycin was carried out by studying its effects on respiration and protein synthesis rates both in short- and in long-term experiments. The former were performed on rice- and carrot-cultured cells by monitoring oxygen consumption and radioactive amino acid incorporation rates, the latter on barley or common cowpea seedlings by following oxygen consumption and alpha-amylase accumulation rates. While short-term exposure to antibiotic concentrations close to those causing severe growth inhibition did not appear to affect the investigated parameters substantially, long-term treatment led to remarkable, though not dramatic, effects. Such effects, as judged by comparison with those induced by cycloheximide and chloramphenicoI, could not be ascribed to a primary inhibition of plant-cell protein synthesis.