A MORPHOMETRIC ANALYSIS OF HETEROPHYLLOUS LEAF DEVELOPMENT IN RANUNCULUS-FLABELLARIS

Environmentally induced heterophylly provides a useful model system for studying the developmental basis of differing leaf shapes. The semiaquatic Ranunculus flabellaris exhibits typical heterophyllous shape variation with change in water level: aerial leaves have short lobes, while lobes of leaves produced underwater are elongate. Submergence in a 25 mu M abscisic acid solution (ABA) produces an aerial-like leaf shape. In this morphometric study, x and y coordinates of nine landmarks of leaf outlines were captured from video images, and linear dimensions between the landmarks were used in multigroup principal components analysis as a method to quantify the timing of developmental divergence in leaf shape of plants grown underwater, in air, or in ABA. Shape differences between aerial and water leaves were detected 16 d after leaf emergence, while size differences were not apparent until after 18 d. This developmental pattern represents a very late structural divergence of leaf forms and additionally indicates that leaf shape determination may not be complete until leaves reach maturity. The multigroup principal components analysis indicated that size and shape of developing and mature ABA-treated leaves are most similar to aerial leaves, which is consistent with the hypothesis that endogenous levels of ABA regulate leaf shape change in this heterophyllous species.