Studies in the Alismataceae. V. Experimental modification of phyllotaxis in pseudostolons of Echinodorus tenellus by means of growth inhibitors

Abstract

Treatment with triiodobenzoic acid (TIBA), N-dimethylamino succinamic acid (B-995), and (2-chloroethyl)trimethylammonium chloride (CCC) can modify the pattern of development of the pseudostolons of Echinodorus tenellus. In particular, CCC and B-995 can with a high degree of success suppress the normal reversal of genetic spiral of the pseudostolon. Other aspects of phyllotaxis, including phyllotaxis of lateral buds, are not affected by CCC and B-995.The pseudostolons, as previously described, are modified inflorescences bearing bracts in false whorls of three, and a vegetative bud in the axil of the first bract of each set after the first. After passing through a brief stabilizing phase the pseudostolon enters a stable state in which the direction of genetic spiral of the main axis reverses with the initiation of the second bract of each set, and in which the genetic spiral of the lateral vegetative bud is quite consistently homodromous with that of the main axis at the time of initiation of the bud.The experimental findings are discussed in relation to the earlier descriptive and analytical studies of E. tenellus. Some previously erected hypotheses relating to control of phyllotaxis in this plant are invalidated. It is suggested that in E. tenellus determination of maintenance or reversal of genetic spiral occurs within a short span of development between the initiation of the first and second bract of each set, and that direction of genetic spiral in the pseudostolon and its vegetative laterals may be controlled by mechanisms independent of those controlling other aspects of phyllotaxis such as divergence angle.