EFFECTS OF ZARILAMIDE ON MICROTUBULES AND NUCLEAR DIVISION IN PHYTOPHTHORA-CAPSICI AND TOBACCO SUSPENSION-CULTURED CELLS

Zarilamide inhibited nuclear division in germinating zoospore cysts of Phytophthora capsici at concentrations which caused only partial inhibition of growth. Morphological effects and inhibition of germ tube elongation occurred after nuclear division had been arrested. Mitosis was arrested very rapidly after adding the compound to germlings about to undergo their first nuclear division, and this was accompanied by destruction of the microtubule cytoskeleton as revealed by immunofluorescence microscopy. The antimicrotubule agent colchicine caused similar effects to those of zarilamide on nuclear division, germ tube morphology, and microtubules in P. capsici. Zarilamide inhibited growth of tobacco roots and caused swelling of the root tips. In tobacco suspension-cultured cells zarilamide produced an accumulation of cells in arrested metaphase, the absence of normal mitotic figures, and the disappearance of both cortical and spindle microtubules. These results suggest that the mechanism of action of zarilamide in P. capsici and tobacco involves destruction of the microtubule cytoskeleton, and a consequent inhibition of mitosis. © 1991.