Detection, characterization and phytotoxic activity of AB021-a and -b, two new macrolide polyene antibiotics

Screening for fungicidal activity carried out on culture broths of soil Streptomyces strains resulted in the isolation of two new macrolide polyene antibiotics, AB021-a and AB021-b, endowed with good protective activity against some plant diseases. These compounds had no effect on seed germination or seedling development, while they strongly inhibited the growth of rice, carrot and periwinkle cells in liquid suspension culture. This inhibition may be ascribed to the lack of the cuticular barrier in these materials. Within a short period of incubation, some parameters connected with membrane permeability of rice, carrot and periwinkle cells were affected. An increase of oxygen consumption also occurred. Incubation of beetroot discs with AB021 led to increased conductivity of the external medium. In addition, a leakage of betacyanin occurred, suggesting a modification of transport processes, also at the tonoplast.