Postgenital carpel fusion inCatharanthus roseus

Abstract

During the postgenital fusion process between the distal carpel tips inCatharanthus roseus, the convex external cell walls of the opposing epidermal layers contact randomly with no interlocking of the cells occurring. The convex cell walls become appressed in places, but intercellular spaces are formed in regions where contact is not complete. In the regions where the walls are appressed, extensive cytoplasmic activity indicates that modification of the walls occurs to effect the adherence of the opposing epidermal walls. Both the rough endoplasmic reticulum and the Golgi apparatus appear to be involved in a process of wall modification through the deposition of wall materials and/or partial enzymatic degradation followed by repolymerization of wall constituents. Periclinal divisions occur in the epidermal layers soon after contact and simultaneously with the secretory activity that modifies the fusion walls. Following the completion of the fusion response, the fused cell walls in the compound ovary region can be distinguished by their double thickness, the trapped cuticle, the so-called pectin layer, and a lack of plasmodesmata. In closely appressed regions of the fusion wall, the cuticle is difficult to detect because newly deposited wall materials have infiltrated this layer. New wall materials are added during fusion by intussusception and are probably composed of matrix wall components and not of fibrillar cellulose. The deposition of these matrix materials apparently effects adhesion of the contacting cell walls. Ultrastructural observations of the cells in the stigmatic region verify findings made by light microscopy that cell differentiation and expansion modify the cell walls sufficiently to make the line of fusion difficult to identify. The major conclusions on postgenital union inC. roseus are summarized.