QUANTITATIVE CHANGES IN NUCLEAR DNA ACCOMPANYING POSTGERMINATION EMBRYONIC DEVELOPMENT IN VANDA (ORCHIDACEAE)

Abstract

Nuclear DNA was measured cytophotometrically in sections and isolated nuclei of the developing embryo of Vanda . The data were interpreted in terms of developmental stage and spatial relationships of the nuclei within the embryo. An equal amount of DNA was found in all meristematic nuclei regardless of the developmental stage of the embryo and was taken as the 2C value. Most of the nuclei in the parenchymatous region fell into the discrete DNA classes, 2C, 4C, and 8C. A significant number, however, had DNA contents above 8C but could not be grouped into classes based on a whole‐number multiple of 2C. Nuclear size was found to vary in direct proportion to DNA content through 8C. Above 8C, correlation between nuclear size and DNA content was poor. The amount of DNA in the nuclei of the parenchymatous region was shown to increase in direct proportion to the distance of the nucleus from the meristem. The average amount of DNA in parenchymal nuclei above 8C was found to increase with the developmental stage of the embryo. Mechanisms which might account for the observed changes in DNA per nucleus are discussed.