RELATIONSHIP BETWEEN ENDOPOLYPLOIDY AND CELL-SIZE IN EPIDERMAL TISSUEOF ARABIDOPSIS

Relative quantities of DNA in individual nuclei of stem and leaf epide rmal cells of Arabidopsis were measured microspectrofluorometrically u sing epidermal peels. The relative ploidy level in each nucleus was as sessed by comparison to root tip mitotic nuclei. A clear pattern of re gular endopolyploidy is evident in epidermal cells. Guard cell nuclei contain levels of DNA comparable to dividing root cells, the 2C level (i.e., one unreplicated copy of the nuclear DNA). Leaf trichome nuclei had elevated ploidy levels of 4C, 8C, 16C, 32C, and 64C, and their cy tology suggested that the polyploidy represents a form of polyteny. Th e nuclei of epidermal pavement cells were 2C, 4C, and 8C in stem epide rmis, and 2C, 4C, 8C, and 16C in leaf epidermis. Morphometry of epider mal pavement cells revealed a direct proportionality between nuclear D NA level and cell size. A consideration of the development process sug gests that the cells of highest ploidy level are developmentally oldes t; consequently, the developmental pattern of epidermal tissues can be read from the ploidy pattern of the cells. This observation is releva nt to theories of stomate spacing and offers opportunities for genetic analysis of the endopolyploidy/polyteny phenomenon.