ESTABLISHMENT OF A CELL-TO-CELL COMMUNICATION PATHWAY BETWEEN SEPARATE CARPELS DURING GYNOECIUM DEVELOPMENT

In the evolutionarily advanced angiosperm flower, postgenital fusion i s often involved in the formation of the female reproductive organ, th e gynoecium. In the present study, we report on the early establishmen t of a cytoplasmic cell-to-cell communication pathway between the two fusing carpel primordia in Catharanthus roseus L. (periwinkle). Upon c arpel contact, diffusible factors move between the two carpels to init iate the rapid redifferentiation of epidermal cells into parenchymatou s cells, resulting in carpel fusion. Microinjection of the lipid-imper meable molecule, Lucifer Yellow CH (LYCH), into cells on either side o f the epidermal fusion plane revealed that cytoplasmic continuity was established very early in this redifferentiation process. Electron-mic roscopic analysis confirmed that this inter-carpel cytoplasmic couplin g was established by the formation of plasmodesmata produced between t he contacting epidermal cells. The evolution of and role for this inte r-carpel communication pathway is discussed in terms of the coordinate development of the gynoecium and its overall effect on reproductive f itness.