The Constancy of Desoxyribose Nucleic Acid in Plant Nuclei

Abstract

The amt. of dexosyribose nucleic acid (DNA) in individual nuclei of Tradescantia spp. and Zea mays was estimated by photometric detns. through a microscope using monochromatic light. By projecting the microscope image on a field diaphragm, an area 2, 3, 4 or 5 mm. in diam. in the center of the nuclear image was allowed to fall on the phototube. Measurements of corn tissue were made at 560 m[mu], the absorption peak of the Feulgen dye, and of Trade scantia tissues at 615 m[mu]. In non-dividing tissues nuclei with 2, 4, 8, 16 or 32 times the haploid amt. (C) occurred, with a distr. as follows C for microspore nuclei (tetrads), young generative nuclei and tube nuclei in Tradescantia and for the microgametic nuclei in the mature pollen of Zea: 2C or 4C for most nuclei in both spp; 8C for Tradescantia stamen hairs; and 8C or 16C in Zea root and root cap and in the scutellum nuclei. The aleurone and endosperm nuclei of Zea fell into the series 3:6:12:24. The nuclei of major vessels of the root, measured up to 1500 [mu] from the tip, gave classes from 4C to 16C or 32C in ascending order, with 6 to 12 nuclei in each class. Between these groups of nuclei 0 to 6 intermediate values were found, which might occur only during periodic DNA doubling as in large vessel cells, or in prepn. for cell division. Mitotic studies in the root and leaf meristem of Zea and in the root meristem and sporo-genous tissue of Tradescantia gave classes of 2C to 4C for interphase nuclei, 4C for prophase, and 2C for telophase. During meiosis in Tradescantia. the microsporocytes showed 2C just prior to the onset of meiosis, increasing during leptotene and zygotene to 4C. The microspore nuclei (tetrads) had C, increasing to 2C before the microspore mitosis, which gave tube and generative nuclei with C amts. The generative nucleus increased to 2C before anthesis and divided to form two microgametic nuclei with C amts. Nuclei of T. paludosa contained approx. 10 x the DNA found in corn nuclei from similar tissues. In Tradescantia spp. a doubling in chromosome no. was correlated with a doubling in amt. of DNA. A comparison between two strains of Zea showed that the strain with a small amt. of heterochromatin had 10% more DNA in root and leaf nuclei than a strain with several B chromosomes and knobs. It is suggested that the varying amt. of DNA may be assoc. with multiple chromonemal sets.