GRAVISTIMULATED ASYMMETRIES IN THE OUTER EPIDERMAL-CELL WALLS OF GRAVIRESPONDING COLEOPTILES

Gravitropic plant growth is due to gravistimulated asymmetric extensio n rates of the affected flanks of the graviresponding organ. Different ial growth of the upper and lower flanks (UFs, LFs) of graviresponding plant organs may in principle be achieved by various biochemical and/ or biophysical asymmetries. The gravistimulated mechanism(s) by which the different growth rates are determined is still unresolved, as is t he mechanism of IAA-regulated growth. The purpose of this brief review is to summarize and critically evaluate data concerning gravistimulat ed asymmetries, especially with respect to the interface of the plasma membranes and of the extension-restricting, load-bearing epidermal ce ll walls (Masuda and Yamamoto 1972 Physiol Plant 27: 109-115). In addi tion, recent results obtained by the author in experiments with rye co leoptiles will be presented and discussed in the context of a tentativ e model of gravistimulated wall asymmetries temporarily causing differ ential growth.