Morphogenetic factors controlling differentiation and dedifferentiation of epidermal cells in the gynoecium of Catharanthus roseus : II. Diffusible morphogens.

During postgenital fusion of the distal adaxial surfaces of the two originally separate carpel primordia of Catharanthus roseus (L.) G. Don, approx. 400 epidermal cells undergo rapid dedifferentiation into parenchymatous cells. To characterize the mechanism of the induction of dedifferentiation, various types of both water-permeable and water-impermeable barriers were placed between pre-fusion carpels. Barriers which did not allow the passage of water-soluble agents blocked dedifferentiation. Barriers which allowed passage of water-soluble agents did not block dedifferentiation of the contacting epidermal cells, implicating a diffusible agent or "morphogen" as the factor responsible for dedifferentiation. Experiments with barriers of known pore size demonstrated that the molecular weight of this morphogen was less than 1000. The two cell walls and thin cuticle present at the site of this postgenital fusion do not block the movement of some substances between the fusing carpels. Tracer studies with tritium-labeled asparagine confirmed that substances can be transported across the fusion plane.