Pollination in Lupinus nanus Subsp. Latifolius (Leguminosae)

Abstract

Floral morphology and phenology and the timing of stigmatic receptivity and pollen viability were studied to elucidate the mechanisms by which self-pollination in Lupinus nanus subsp. latifolius is minimized under natural conditions. Pollen germination and pollen tube growth suggest that a physiological self-incompatibility system does not exist. Instead, self-pollination is minimized by protandry and by a collar of peristigmatic hairs, which initially inhibit access of autologous pollen to the stigma. These hairs subsequently wilt, permitting self-pollination of unvisited flowers. Pollen germinates in vivo one day before substantial metabolic enzyme activity can be detected. Citric acid cycle enzymes are not detectable in pollen, but those of anaerobic metabolism are. Beginning on the second day postanthesis, stigmatic secretions exude from weak areas on lateral walls of the elongate epidermal papillae, welling up in the interstices between these cells. This contrasts with the stigmas of other papilionoid legumes, in which secretions accumulate beneath the cuticle covering the stigmatic cells, and the often-thin cuticle must be ruptured before pollen and exudate can come into contact.