An analysis of morphogenesis of the reproductive whorl of Acetabularia acetabulum

Acetabularia acetabulum (Linn.) P.C. Silva, is a useful system for studying changes in shape because it is large, morphologically complex unicell. The middle, or gametophore lobe of the cap grows radially from the stalk axis as a disc and the fully grown cap can be one of several shapes: flat, concave, convex, and saddle. The shape of the cap normally changes during the first three and a half weeks of reproductive development: individual caps within a population change shape in a stereotypical progression, with the majority proceeding from concave to flat to saddle. Marking the existing surface of caps with carbon grains revealed that the majority of growth occurs near the center, not at the perimeter, of caps. The shape of the mature cap appeared to be independent of algal height, number of gametophores per cap, and final cap diameter. Removing the rhizoid, which contains the nucleus, suggested that the contribution of the nucleus may be important for changes in shape during early cap growth. Based on these data, we present a simple model of cap shape development that suggests both differential growth and biophysical factors may contribute to the final shape of caps of A. acetabulum. Received: 7 January 1998 / Accepted: 7 March 1998