[en] When a high dose of gamma irradiation was applied to the seeds (500-1000 Gy) or directly to the inflorescences (3000 Gy) of Nicotiana tabacum L. var. xanthi Dulieu, there was a marked decrease in the DNA content (20 to 40 %) both of the nucleus of the pollen mother cells (PMCs) at pachytene and the two endomitotic nuclei of the corresponding tapetum cells. When inflorescences were directly irradiated (3000 Gy) before ³H-thymidine application, there was a reduction in the labelling of the PMCs and tapetum (75 to 94 %) due both to an inhibition of DNA synthesis by the chromatin remaining in situ and a loss of chromatin by elimination of chromosomal fragments. Under these last conditions, the incorporation of ³H-uridine in the chromatin, nucleolar and cytoplasmic RNA was also strongly inhibited (70 to 90%) in PMC and tapetum cells. (author)

[en] Gamma irradiation of seeds (100 to 1000 Gy) or inflorescences (3000 Gy) of Nicotiana tabacum L. var. xanthi Dulieu mainly induced chromatoclastic effects affecting the microspore mother cells (MMCs) during meiosis: chromosome fragmentation, chromosome stickiness promoting the formation of chiasmas even between non-homologous chromosomes, single or multiple chromosomal bridges during anaphases and telophases I and II and irregular chromosomal disjunction. In plants raised from irradiated seeds, the frequency of abnormal meiotic figures and the rate of pollen sterility were directly related to the gamma ray dose. Gamma irradiation also induced the early dysfunction of the tapetum (tapetal degeneration was already visible at pachytene) with nuclear pycnosis or an expanded and sticky chromatin network and this no doubt contributed to pollen sterility. (author)