The effect of fusicoccin on the common wheat genome

The effect of fusicoccin on the common wheat genome (cv. Mironovskaya 808) during early phases of seed germination was studied. It was shown that fusi coccin: (1) increased the number of cells with one or two nucleoli and decr eased the proportion of cells containing three and four nucleoli; (2) enhan ced the total volume of nucleoli per nucleus at a concentration of 0.68 mg/ l; (3) did not activate additional rRNA genes on chromosomes 1B and 6B; (4) did not activate the latent nucleolus organizer regions on chromosomes of genome D; (5) induced associations of nucleolus organizer regions on B-geno me chromosomes; (6) significantly enhanced mitotic activity in apical meris tem of seedling root tips and promoted the first peak of mitoses; the effec t disappeared after 44 h of seed imbibition; (7) in contrast to gibberellin , did not synchronize cell division; (8) did not cause chromosome and chrom atid aberrations or increase the frequency of sister chromatid exchanges at physiologically active concentrations. Presumable mechanisms of fusicoccin -induced activation of rRNA genes are discussed in relation to the identifi cation of the fusicoccin receptor belonging to the GF14 proteins with an in tracellular binding site, to the detection of endogenous fusicoccin in plan ts in vivo, and to fusicoccin-induced activation of gene transcription.