Dna in Gametogenesis and Embryogeny in Tradescantia

Abstract

Within recent years evidence has come from several lines of research that the gene is either composed of, or is at least intimately associated with, desoxyribose nucleic acid (DNA). Experiments in microbial genetics have shown that only the DNA fraction of the bacterial protoplast is capable of transforming other bacteria to the genetic type from which the DNA was originally derived (2). Further, both chemical extraction and photometric studies have supported the view that within a plant or animal the amount of DNA per nucleus occurs in simple multiples of a basic (haploid) amount (see references 30, 34 for review). Such consistent quantitative behavior could account, at least in part, for the remarkable genetic constancy of successive cell generations and has been presented as evidence for close relationship between DNA and the stable characteristics of the gene (see reference 30 for review).The nucleus has been known for some time to embody several other forms of stability. Studies on uptake of radioactive phosphorus (p32) have shown a striking metabolic stability in the DNA molecule. Autoradiographic studies (see references 11, 33, 16, 8 for review) indicate that although incorporation of p32 into DNA is high in tissues where DNA synthesis is occurring, it is very low in some non-dividing tissues. Furthermore, chromatographic separation and quantitation of the purines and pyrimidines of DNA indicate that the proportions of the purine and pyrimidine bases seem to be constant for a species (6,35). In contrast to the stability of DNA, ribose nucleic acid (RNA) and some protein fractions appear to vary and Ris (22) has suggested that constancy of DNA represents nuclear stability presumably related to the stable aspects of the gene, while the variability of some protein and RNA fractions represents instabilit~ and change in the nucleus according to cell function.

Double Fertilization in Gnetum gnemon: The Relationship between the Cell Cycle and Sexual Reproduction.

“…Other than the ci rrent investigation of G. gnemon, few studies of seed plants have documented nuclear DNA levels of gametes as well as zygotes (Woodard, 1956;Bennett and Smith, 1976;Friedman, 1991;Mogensen and Holm, 1995;. One of the first, and perhaps most compelling, studies on the relationship between the cell cycle and sexual reproduction was by Woodard (1956).…”

“…One of the first, and perhaps most compelling, studies on the relationship between the cell cycle and sexual reproduction was by Woodard (1956). Based on microspectrophotometry of Feulgen-stained nuclei in Tradescantia paludosa, Woodard (1956) found that egg cell nuclei contain the 1C quantity of DNA through fertilization, and newly formed zygotes contain the 2C amount. Sperm nuclei were not measurable but were inferred to contain the 1C quantity of DNA.…”

“…It is likely that gamete nuclei fuse immediately upon contact to form a 4C zygote nucleus. However, even in 7: paludosa, which expresses G1 karyogamy, union of gametes is rapid, and fertilization stages were rarely observed in sectioned material (Woodard, 1956).…”

“…Unfortunately, reproductive cell cycles have not been adequately investigated in most groups of seed plants, and, with one exception (Friedman, 1991), relationships between cell cycle patterns and sexual reproduction have been derived exclusively from a small number of studies on angiosperms (Taylor and McMaster, 1954;Woodard, 1956;DAmato et al, 1965;Woodcock and Bell, 1968;Mericle, 1970, 1973;Hesemann, 1973;Bennett and Smith, 1976;Ermakov et al, 1980;Bino et al, 1990;Mogensen and Holm, 1995;Sherwood, 1995).…”

Basic Proteins of Plant Nuclei during Normal and Pathological Cell Growth

“…The nuclear class or "C" value for each cell type in Tables I to IV are those reported for DNA content of nuclei of Tradescantia from several laboratories (42,52,59). In Tables V and VI DNA amounts were estimated directly by the usual photometric techniques (54) applied to Feulgen-stained sections adjacent to those on which histone determinations were made.…”