XVI International Botanical Congess

We are studying the leaf habit of the Rolled (Rld) maize mutant. There are three main mutant phenotypes characteristic of the Rld leaf: a straighter longitudinal shape, suppression of normal leaf unrolling causing a transversely rolled lamina, and a reversed top/bottom polarity between the leaf surfaces. The first hypothesis we are testing is that there is a mechanical coupling between leaf rolling and midrib longitudinal shape. According to engineering shell theory, leaf rolling might mechanically straighten the Rld leaf midrib, masking the midrib=s true rest-state longitudinal curvatures. Our first objective was to assess quantitatively whether the Rld midrib is straighter than the wild type. Longitudinal curvatures were determined from photographs of intact leaves and dissected midribs. Comparisons between the wild type and Rld mutant longitudinal shapes suggest that the mature Rld leaf midrib in its rest-state is naturally less curved than the wild type. Leaf rolling does not cause the mutant=s straighter leaf phenotype. In situ, however, the leaf rolling may well decrease longitudinal curvature under self weight. Thus, the Rld mutant appears to be a suitable model to study the relation between tissue polarity and an altered form of curvature development in the maize leaf.