Interaction between Floral Merism and Symmetry: Evidence from Fasciated Mutant of Lupinus angustifolius L. (Leguminosae)

Abstract

A significant diversity of flower structure in angiosperms is defined by few parameters, among which one may list floral merism and symmetry as the most important. However, observation of normal variation in different taxa indicates that high floral merism (more than six organs) is very rarely associated with a monosymmetry. Precise mechanisms underlying this tendency, as well as the mode of interaction between regulatory pathways of floral symmetry and merism, remain unidentified. In this work, we observed the floral ontogeny in normal plants of Lupinus angustifolius L. (Leguminosae), described the floral structure and its variations in fasciated mutant. Our results suggest that monosymmetry is regulated independently from the floral merism, so three types of petals differentiate properly even in flowers with an anomalously high number of organs. However, the adaxial floral domain is the most stable floral part, which is the least susceptible to the fluctuations of merism. This means that some genes responsible for the development of the adaxial flower domain may additionally stabilize it and hence prevent fluctuations of merism in the adaxial domain. The monosymmetry in Leguminosae is a character connected with pollination by insects and requires a precise interaction between all floral parts. That is why fluctuations, which impair this interaction and symmetry, may decrease the pollination efficiency.