The effect of fusicoccin on the common wheat genome (cv. Mironovskaya 808) during early phases of seed germination was studied. It was shown that fusicoccin: (1) increased the number of cells with one or two nucleoli and decreased the proportion of cells containing three and four nucleoli; (2) enhanced 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 B; (5) induced associations of nucleolus organizer regions on B-genome chromosomes; (6) significantly enhanced mitotic activity in apical meristem of seedling root tips and promoted the first peak of mitoses; the effect disappeared after 44 h of seed imbibition; (7) in contrast to gibberellin, did not synchronize cell division; (8) did not cause chromosome and chromatid aberrations and 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 identification of the fusicoccin receptor belonging to the GF14 proteins with an intracellular binding site, to the detection of endogenous fusicoccin in plants in vivo, and to fusicoccin-induced activation of gene transcription.