Differentiation in leaf epidermis

Abstract

Microphotometric studies of the leaf epidermis of four monocotyledons indicate that differentiation is accompanied by DNA increases. High polyploidy (over 16-ploid) may be reached in epidermal cells of Galtonia candicans. DNA is approximately paralleled by total nuclear protein increases.

The large nucleolus apparently contains most of the nuclear RNA of Galtonia, except at mitosis, when chromosomal RNA becomes apparent. Nucleolar volume increases rapidly at first until the cell is midway in development, when it levels off or may even fall. The nucleolus buds and loses volume in mature guard cells. Cell elongation, and DNA and protein increases, cease at maturity.

The final state of differentiation may be related to the initial supply of nucleolar and cytoplasmic material received at mitosis, as well as to environmental differences such as position between or over veins.

Simple stomata may result from the early initiation of polyploidy in epidermal cells, and suppression of induction by guard cells.