Antisymmetry in female strobili of Pinus taeda

Abstract

Spiral structures are a widespread theme in plant morphology, raising considerable interest amongst botanists and mathematicians for their relationship with Fibonacci numbers (see Cooke. 2006 for a recent review). Most of this research has focused on phyllotaxis, the study of the relative arrangement of repeated units, such as leaves around a stem, etc. (Jean, 1994;Adler et al. 1997). Several hypotheses have been provided to explain the pervasiveness of phyllotaxis in plant morphology, such as an increased light reception efficiency in the case of leaves (e.g. Valladares and Brites, 2004;Brites and Valladares 2005), but the understanding of the adaptiveness of phyllotaxis has been elusive.A phenomenon closely related to (but conceptually independent from) phyllotaxis is antisymmetry, the presence of alternative orientations of the asymmetric structures (Palmer, 2005). The female strobili of pines, commonly known as pine cones, are an ideal model system to study antisymmetry in plants. These structures are composed of scales forming a series of spirals, also known as parastichies, which determine the orientation of the cone. The goal of the present study is two-fold. First, we assess whether there are statistically significant deviations from a 50:50 proportion of left-and right-spiraling pine cones. We also test whether there is a genetic predisposition for any given direction by comparing the orientation of cones from the same tree (and thus of the same genotype).Collections were carried out in March 31, 2006 in the campus of the Universidade Federal do Paraná, in Curitiba, in Southern Brazil. A total of 500 cones of the slash pine Pinus taeda (Linnaeus) were collected and scored according to their orientation. In order to test if there is a genetic predisposition toward a given orientation, we collected an additional 20-50 pines from each of five trees (Figure 1).