Poster: Hormones

Abs # 637: The distribution of auxins in gametophytes of the moss, Physcomitrella patens.

Presenter:	Akister, Bevin J., akisterb@uregina.ca
Authors	Akister, Bevin J. (A)   Ashton, Neil W. (A)
Affiliations:	(A): University of Regina

Although the occurrence and developmental roles of auxins in mosses are well documented, little has been reported about auxin distribution in these plants. We have investigated auxin distribution patterns in Physcomitrella patens gametophytes possessing a transgenic GUS reporter gene controlled by the auxin-responsive MAS promoter. In each of three transgenic strains, we demonstrated that the plasmid vector containing a MAS-GUS cassette had been integrated at a unique site in the P. patens genome. One transformant, LT II-2, exhibited strong expression of the GUS reporter gene, providing a suitable system for studying endogenous and exogenous auxin distribution. In untreated plants, enhanced GUS expression, reflecting elevated auxin levels, occurred in leaf bases, midribs and margins as well as leaf apical cells. The application of auxin efflux inhibitors usually resulted in intense GUS expression in basal regions of leaves positioned at the stem apex. The application of exogenous IAA or NAA stimulated GUS expression especially in buds and the apices of leafy gametophores, both of which became considerably elongated. We suggest that auxins accumulate preferentially in cells of buds and gametophore apices and may cause their elongation. Studies with auxin transport inhibitors suggest that endogenous auxins may be synthesized at the bases of apical leaves. Interestingly, dark-grown gametophores of the transgenic moss were greatly etiolated but exhibited little/no GUS expression. However, GUS activity was detected in the apices of these leafy shoots within one day of returning them to the light. Therefore, auxin synthesis or accumulation may be light-dependent and, in contrast to light-grown moss, gametophore development in the dark may not require auxins.