LEAF DEVELOPMENTAL PLASTICITY OF RANUNCULUS-FLABELLARIS IN RESPONSE TO TERRESTRIAL AND SUBMERGED ENVIRONMENTS

Environmentally induced developmental plasticity is characteristic of many heterophyllous semiaquatic species, including Ranunculus flabella ris. Underwater shoots of this species form leaves with elongate narro w lobes, while aerial shoots form leaves with shorter, broader lobes. In this study, a series of transfer experiments was undertaken to dete rmine the competence of developing leaves to respond to a change in en vironmental conditions. Plants were transferred from terrestrial to su bmerged conditions at 8, 16, and 24 days after the approximate time of initiation of leaf 4; these times correspond to the developmental sta ges before differences in size and shape of aerial and underwater leav es can be detected, the time of divergence, and postdivergence when le aves are about half expanded. Morphological and anatomical traits of m ature leaves grown terrestrially, submerged, or after transfer at 8, 1 6, or 24 days were measured and assessed using analysis of variance an d principal components analysis. We found that some traits of leaves ( such as lobe number) transferred at 8 days were similar, but not ident ical, to those of the water control, indicating that some features are determined prior to structural divergence. Leaves transferred at 16 a nd 24 days were intermediate between the land and water controls in mo st respects, indicating that traits such as epidermal and mesophyll ce ll shape are determined gradually during expansion. Other anatomical f eatures, such as development of a palisade layer and extent of interce llular space, did not differ between transfer treatments and the water control, indicating that these features can respond to ambient condit ions late in development.