The Growth of the Nucleus in Dividing and Non-dividing Cells of the Pea Root

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Abstract
The growth of the nucleus and the cell in the pea root was followed through the mitotic cycle and subsequently in post-mitotic development by comparing cells and nuclei from the meristem, at different stages of interphase, and cells and nuclei from two regions of the enlarging zone of the root. Measurements of cell and nuclear volumes were made in sections of fixed roots. Measurements of nuclear volume, DNA content, and dry mass were made on isolated nuclei. Growth in the mitotic cycle was characterized by a doubling of DNA and nuclear dry mass and a five-fold increase of nuclear volume. Since cell volume doubled, a differential hydration of cytoplasm and nucleus is inferred. Post-mitotic growth was characterized by a four-fold or greater increase in cell volume, with vacuolation and a continued increase of cytoplasmic constituents, but a cessation of nuclear growth except by uptake of water; the only increase in nuclear dry matter appeared to be in cells becoming endopolyploid. The concentration of dry matter in the nucleus fell as the nuclei enlarged in the mitotic cycle and in post-mitotic growth. The relationships between the measured parameters are examined to see whether they might be indicative of causal relationships.