Biomechanical analysis of the Rolled (Rld) leaf phenotype of maize

The pleiotropic effects of the Rldl-O/t mutation of Zea mays (Poaceae) on l eaf phenotype include a suppression of normal transverse unrolling, a rever sed top/bottom epidermal polarity, and an apparently straighter longitudina l shape. According to engineering shell theory, there might be mechanical c oupling between transverse and longitudinal habit, i.e., the leaf lolling i tself might produce the longitudinal straightening. We tested this possibil ity with quantitative curvature measurements and mechanical uncoupling expe riments. The contributions of elastic bending under self weight, mechanical coupling, and rest state of leaf parts to the longitudinal and transverse habit were assessed in Rld-O/+ mutants and a population of sibling +/+ segr egants. Elastic bending and curvature coupling are shown to be relatively u nimportant. The Rld-O/+ mutation is shown to after not only the unrolling p rocess, but also the developmental longitudinal curving in the growing leaf , leading to a straighter midrib and a rolled lamina. The Rldl-O/+ mutant i s thus a suitable model to study the relation between tissue polarity and d ifferential curvature development in the maize leaf. Since on the abaxial s ide of the leaf more abundant sclerenchyma is found in +/+ than in Rldl-O/, a gradient in sclerification may contribute to the development of midrib curvature.