Autoradiographic and microphotometric studies of desoxyribose nucleic acid during microgametogenesis in Lilium longiflorum

Variations in Sulfhydryl Concentration During Microsporocyte Meiosis in the Anthers of Lilium and Trillium

Anthers of lily and trillium were followed with respect to variations in protein and soluble sulfhydryls during meiosis and mitosis of the sporogenous tissue. In lily, the meiotic and mitotic cycles are each preceded by a rise in soluble -SH; in trillium there is only one rise which precedes meiosis. During division there is a marked drop in soluble -SH and a rise in soluble disulfides. Protein -SH remains approximately constant until diakinesis or metaphase when it falls briefly.

Evidence for Two Metabolically Distinct Types of Ribonucleic Acid in Chromatin and Nucleoli

Patterns of radioisotope incorporation are useful characteristics in describing cellular RNA fractions, and have indicated a distinctive "nuclear" RNA. In order to characterize the RNA fractions of the two nuclear components, nucleoli and chromatin, and to determine thereby the precise localization of the RNA typical of isolated nuclei, time-courses of P(32) incorporation into nucleolar, chromosomal, and cytoplasmic RNA of Drosophila salivary glands have been determined from autoradiograms. Two experiments are reported which cover 12 and 18 hour periods, including an initial 2 hour feeding on P(32). Concentrations of RNA-P(32) (identified by ribonuclease digestion) were determined by grain counts. After 1 hour only the nucleolar RNA is labelled. Activity is detectible in chromosomal and cytoplasmic RNA after the 2nd hour. The nucleolar fraction reaches its maximum activity shortly after transfer of the larvae to non-radioactive food, the other fractions several hours later. Maximum activities persist in the chromosomal and cytoplasmic fractions; nucleolar activity decreases after the 9th hour. The observed differences in times at which incorporation begins and maximum activities are reached, and in maintenance of maximum activities indicate that chromosomal and nucleolar RNA are distinct fractions. The metabolic characteristics which have been ascribed to "nuclear" RNA apply only to the nucleolar fraction.

Microspectrophotometry of cell nuclei stained with the Feulgen reaction. IV. Formation of tetraploid nuclei in rat liver cells during postnatal growth

1. DNA contents of the individual parenchymal nuclei of rat livers during postnatal growth were estimated by microspectrophotometric apparatus, and different ploidy classes of nuclei were classified by their DNA contents. With the same material the total number of parenchymal nuclei in the liver was counted microscopically. 2. If the DNA content of nuclei encountered most frequently in several tissues represents the diploid class, the ploidy classes of the rat liver cell nuclei correspond to di-, tri-, tetra-, and octoploid, with the di- and tetraploid ones predominating considerably. 3. In suckling rats (below 25 gm. of body weight) the liver parenchyma is composed almost exclusively of cells with diploid nuclei, whereas in young rats (above 80 gm.), of tetraploid nuclei. In the growth stage between 25 and 80 gm., there is a remarkable replacement of the diploid nuclei by the tetraploid ones. However, in the liver of adult rats weighing more than 150 gm., any increase or decrease in the frequency of diploid and tetraploid nuclei is hardly observable. In such rats, the nuclear population of the liver parenchyma seems to reach a cell-ecological equilibrium which is considered to be a stable one. 4. It is shown that such nuclear populations and the total number of nuclei in a liver are controlled by the growth state, and not by the age. 5. The decrease in the total number of diploid nuclei and the increase in tetraploid nuclei in the growing livers of rats weighing from 40 up to 130 gm. can both be explained by the hypothesis that the tetraploid nuclei originate from the interphase diploid nuclei without involving mitosis. This hypothesis implies that mitosis is confined to the reproduction of diploid cells alone. 6. It is suggested that, in general, the synthesis of DNA does not necessarily result in the formation of visible mitotic chromosomes. 7. Mitotic time and generation time of diploid nuclei and the percentage of the tetraploidization from diploid nuclei are calculated and discussed.

DNA in gametogenesis and embryogeny in Tradescantia

A microphotometric study of various Feulgen-stained gametophytic and sporophytic nuclei of Tradescantia paludosa was made to test the hypothesis that DNA is maintained in multiples of a basic unit within all cells of an organism. A multiple relationship was found in all tissues analyzed. The lowest amount of DNA was found in gametophytic nuclei, approximately twice and four times this amount in sporophytic nuclei, and approximately three and six times this amount in endosperm nuclei. Intermediate amounts of DNA were found only in tissues presumably undergoing an interphase synthesis of DNA preceding either cell division or endomitosis. It is concluded that within the limitations of present methods of measurement, DNA amounts show a quantitative behavior which supports the "constancy" hypothesis. Such quantitative stability of DNA gives support to the concept that DNA is associated with the stable elements of the gene.