Flower Bud Size Research Articles

Effets des radiations gamma sur les stades successifs de developpement du gametophyte male de tabac

The effects of three exposures of gamma rays (1,2,4 kR) on the successive developmental stages of the male gametophyte of tobacco were carried out in order to investigate their radiosensitivity. The radiobiological parameters considered were: pollen fertility of the flowers irradiated at the bud stage, the embryonic development 7, 9 and 11 days after hand pollination with pollen coming from irradiated floral buds, seed-setting, mean weight of 100 seeds, germination of seeds, cotyledon abnormalities and aberrant mitotic anaphases in the root tips of the M 1 seedlings. All these analyses show that radiosensitivity is low in the early microspore stages and increases up to the haploid mitosis. Afterwards, during the whole binucleate stage, radiosensitivity decreases to a minimum some days before anthesis (flower bud size: 51 mm) and increases again during the last two days. The changes in radiosensitivity seem to be related to the DNA synthesis during the microspore stage whilst, for the binucleate stages of the male gametophyte, sensitivity may be related to the synthesis and the hydrolysis of polysaccharides in the cytoplasm of the pollen grain. Because of the persistence of chromosomal aberrations in root tips of the seedlings obtained from irradiated microspores and pollen grains, it appeared that by this type of radiation treatment in tobacco, it is not possible to obtain plants completely heterozygous for some induced mutations.