2017 Volume 29 Issue 1 Pages 75-80
Male flowers of Ceratophyllum demersum show a variable phyllotactic arrangement (merosity); spiral, trimerous, tetramerous and chaotic. We have demonstrated that, in a young primordium of male flower, both tepals and stamens show unidirectional initiation, first initiating on the abaxial side of the floral apex and only later on the adaxial side. In a flower at later developmental stage, inner stamens always show a spiral pattern. Our study indicated that the unidirectional initiation in early development is probably due to the pressure imposed by the leaf primordium at a higher node, and the spiral arrangement should be the original pattern in the stamen initiation. This result indicates similarities of the floral development in Ceratophyllum, at least in male flowers, with those of basal angiosperms except Nymphaeales. We conclude that mechanical forces on the adaxial side of the flower meristem are an important factor explaining the meristic variation not only in flowers of this species but also in flowers of all angiosperms. To examine this hypothesis, we have developed an experimental system using a micromanipulator with silicon device to produce an artificial mechanical force on the abaxial side of the young floral apex of Arabidopsis thaliana and to induce the development of flowers other than tetramerous ones. We have obtained some distorted flowers probably due to the mechanical force imposed by this device.
