THE DISTRIBUTION OF TRITIATED THYMIDINE IN TETRAD NUCLEI OFHAPLOPAPPVS GRACILIS

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Abstract
Incorporation of tritiated thymidine in nuclei of pollen mother cells of Haplopappus gracilis was accomplished by feeding the labelled thymidine to intact buds of the plant. The buds were harvested when the outer florets were both at the diad and tetrad stage of meiosis. The distribution of the label in diad and tetrad nuclei was determined by examining autoradiographs of squashes of anthers taken from appropriate florets. Whereas all the diad nuclei examined appeared to have the label equally distributed between the 2 nuclei, about half of the tetrads showed an unequal distribution of label among their 4 nuclei. Implications that the distribution of the label may have regarding the structure and replication of the chromosomes are discussed.