Effects of gamma-irradiation-induced mutation on upland cotton pollen grains

Despite the demonstrated value of gamma ray as a tool in plant mutation research, in the genetic plant species upland cotton (Gossypium hirsutum L.), such mutations have not been extensively studied. To investigate these questions, the upland cotton cultivar 'Sumian 22' pollen grains were irradiated by gamma rays (20Gy). The irradiation effects on pollen grains were tested considering the ultrastructure changes in the exine and interior walls of pollen grains, their germination rate, DNA polymorphism in the pollen grains, the actin filament in pollen tube, fertilization, and boll development after the pistils were pollinated by the pollen grains which were irradiation with γ-rays. As compared with the control, although the cell structures inside the pollen grain were destroyed, its exine and interior walls of the pollen grain were not etched. The amount and the density of pollen grain inclusions decreased and the size of the lacuna and starch granules increased. Pollen grain germination rate decreased by 37%. The number of pollen tubes in the style declined by 38%, but the growth speed of the tubes did not change. All of the pollen tubes reached the end of the style at 13-h after pollination. This result was consistent with that of the control. Also, the weight and the diameter of the ovary decreased and shortened. No evident change of the fecundation time of ovule was observed. The significant difference on DNA polymorphism was found between irradiation pollen grain and control after pollination by Simple sequence repeats (SSR) molecular marker. The actin filament of the apical domain in pollen tube was destabilized, and in the approximately apical domain, the actin cytoskeleton component disappeared. Various mutants were appeared in the M1 progenies. These results indicate that gamma rays can cause a series of biological changes in irradiated-pollen grains and their progenies of upland cotton. (author)