Abstract
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.
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