Morphogenetic factors controlling differentiation and dedifferentiation of epidermal cells in the gynoecium of Catharanthus roseus : I. The role of pressure and cell confinement.

To test the morphogenetic role of equilateral stress and physiological confinement in dedifferentiation of epidermal cells, impermeable barriers of goldmetal foil were placed between the postgenitally fusing epidermal surfaces in the gynoecium of Catharanthus roseus (L.) G. Don. Cells contacting the foil barrier were firmly compressed and air spaces were almost eliminated, thus mimicking an internal cellular environment. However, the cells adjacent to the barriers retained epidermal characteristics and did not dedifferentiate. In contrast, epidermal cells that could establish a direct cell-to-cell contact along the margins of the barriers rapidly dedifferentiated as in normal development. The results indicate that neither physical stress on the cell surfaces nor modifications in gradients of gases or volatile products around the cells control the process of epidermal dedifferentiation. The morphogenetic stimulus in this system requires direct cell contact, and may thus consist of a diffusible messenger molecule or some kind of cell surface interaction. Aspects of this cell interaction and of epidermal cell differentiation generally are discussed.