THE MECHANISM OF SOMATIC ASSOCIATION IN COMMON WHEAT, TRITICUM AESTIVUM L. IV. FURTHER EVIDENCE FOR MODIFICATION OF SPINDLE TUBULIN THROUGH THE SOMATIC-ASSOCIATION GENES AS MEASURED BY VINBLASTINE BINDING

Treatment with the antitubulin vinblastine was found to disrupt the spindle system in dividing root-tip cells of common wheat, Triticum aestivum L. Genotypes lacking the somatic association suppressor gene on 5BL, or containing the somatic-association promoter on 5BS, were found to be more sensitive to the treatment. In genetic lines carrying the somatic association suppressor, sensitivity to vinblastine was lower and there was a direct correlation between dosage of the suppressor gene (0, 2, and 4) and the decrease in spindle disruption on exposure to various concentrations of vinblastine. It is concluded that the somatic association genes affect binding ability of spindle tubulin to vinblastine. Since the same genes affect binding of colchicine to tubulin and since the two alkaloids attach to different sites it is assumed that the somatic association suppressor gene has a broad effect on the tubulin molecules which is not confined to a single site. The relevance of genetic control of antitubulin binding to somatic association is discussed.