A MORPHOMETRIC ANALYSIS OF HETEROPHYLLOUS LEAF DEVELOPMENT IN RANUNCULUS-FLABELLARIS

Environmentally induced heterophylly provides a useful model system fo r studying the developmental basis of differing leaf shapes. The semia quatic Ranunculus flabellaris exhibits typical heterophyllous shape va riation with change in water level: aerial leaves have short lobes, wh ile lobes of leaves produced underwater are elongate. Submergence in a 25 mu M abscisic acid solution (ABA) produces an aerial-like leaf sha pe. In this morphometric study, x and y coordinates of nine landmarks of leaf outlines were captured from video images, and linear dimension s between the landmarks were used in multigroup principal components a nalysis as a method to quantify the timing of developmental divergence in leaf shape of plants grown underwater, in air, or in ABA. Shape di fferences between aerial and water leaves were detected 16 d after lea f emergence, while size differences were not apparent until after 18 d . This developmental pattern represents a very late structural diverge nce of leaf forms and additionally indicates that leaf shape determina tion may not be complete until leaves reach maturity. The multigroup p rincipal components analysis indicated that size and shape of developi ng and mature ABA-treated leaves are most similar to aerial leaves, wh ich is consistent with the hypothesis that endogenous levels of ABA re gulate leaf shape change in this heterophyllous species.