Effects of pollination on floral attraction and longevity

The end of a flower's attraction to pollinators may be due to a range of visible cues such as permanent flower closure, a colour change, and withering or abscission of the petals. Floral attraction may be reduced by pollination. Pollination-induced conclusion of floral attraction is often due to a colour change or to flower closure. This may or may not be followed by a reduction in floral longevity, defined as the time to petal withering, wilting or shattering. In a few species floral longevity is increased following pollination-induced flower closure or a pollination-induced change in colour. Floral attraction, therefore, has to be disting uished from floral longevity. A literature survey shows that pollination rapidly reduces floral attraction in numerous orchids, but among other plant families only about 60 genera have been found to show pollination-induced shortening of floral attraction. Although only a few species have been investigated, it was invariably established that the effect of pollination is blocked by inhibitors of ethylene synthesis or ethylene perception, hence is mediated by ethylene. The flowers that cease to be attractive to pollinators, shortly following pollination, tend to be from families that are known mainly to comprise species in which flower longevity, petal colour, or flower closure, is sensitive to exogenous ethylene. This indicates that the effect of pollination on floral attraction is generally mediated by endogenous ethylene. Numerous species reportedly show a decrease in the period of floral attraction after exposure to ethylene, whereas only for a small number of species a decrease in the period of floral attraction induced by pollination has been observed. This discrepancy may be due to the greater attention that has been paid to the effects of ethylene. Nonetheless, the possibility remains that endogenous ethylene has a role in changing perianth form and colour in addition to signalling the occurrence of pollination.