Pollen Signaling and Interorgan Regulation of the Postpollination Syndrome of Flowers

S. D. O'Neill

In: Pollen-Pistil Interactions and Pollen Tube Growth

A. G. Stephenson, and T.-h. Kao (eds.), Amer. Soc. Plant Physiol., Rockville, MD. p. 161-177 (1994)

SUMMARY

Pollination of flowers is a key regulatory event in plant reproduction which initiates a syndrome of developmental events that contribute to successful reproduction. Components of the postpollination developmental syndrome include perianth senescence which contributes to remobilization of nutrients to the developing ovary, pigmentation changes which signal potential pollinators and discourage subsequent visitation, ovary growth, and ovule differentiation in preparation for impending fertilization. These developmental changes collectively function to ensure successful fertilization and embryogenesis. In orchid flowers, postpollination development is precisely and often completely triggered by pollination and thus provide the most extreme example of the pollination regulation of this syndrome of developmental events. This feature makes orchid flowers uniquely suited to the experimental dissection of postpollination regulation.

The postpollination syndrome of development in orchids, including ovary development, involves coordinated interorgan regulation of expression of ethylene biosynthetic genes and ethylene production. In addition, ethylene and auxin together contribute to the regulation of female and male gametophyte development in orchid flowers. Characterization of both the temporal and spatial regulation of the genes encoding ethylene biosynthetic enzymes has led to the development of a model of interorgan regulation of postpollination flower development by spatial separation of expression of ethylene biosynthetic genes and translocation of the hormone precursor, ACC.

These results have provided insights into the mechanism of interorgan regulation of postpollination development and the role of ethylene and auxin in initiating several of these developmental events. In addition, mechanisms that regulate the events leading to autocatalytic ethylene biosynthesis in spatially distinct tissues have been elucidated in this system. Additional research is in progress to elucidate the primary molecular signals associated with the pollination event that initiates the biosynthesis of ACC and ethylene in the stigma because this step reflects the initial signal-response coupling event between pollen and stigma.