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 flabellaris. Underwater shoots of this species form leaves with elongate narrow lobes, while aerial shoots form leaves with shorter, broader lobes. In this study, a series of transfer experiments was undertaken to determine the competence of developing leaves to respond to a change in environmental conditions. Plants were transferred from terrestrial to submerged conditions at 8, 16, and 24 days after the approximate time of initiation of leaf 4; these times correspond to the developmental stages before differences in size and shape of aerial and underwater leaves can be detected, the time of divergence, and postdivergence when leaves are about half expanded. Morphological and anatomical traits of mature leaves grown terrestrially, submerged, or after transfer at 8, 16, or 24 days were measured and assessed using analysis of variance and principal components analysis. We found that some traits of leaves (such as lobe number) transferred at 8 days were similar, but not identical, to those of the water control, indicating that some features are determined prior to structural divergence. Leaves transferred at 16 and 24 days were intermediate between the land and water controls in most respects, indicating that traits such as epidermal and mesophyll cell shape are determined gradually during expansion. Other anatomical features, such as development of a palisade layer and extent of intercellular space, did not differ between transfer treatments and the water control, indicating that these features can respond to ambient conditions late in development.