Antheridiogen Response in Phanerophlebia and Related Fern Genera

Abstract

Antheridiogens are naturally-occurring plant products that act pheromonally to affect sexual expression in the gametophytes of some pteridophyte species. The production of an antheridiogen was first reported by Dopp (1950), who observed that developing gametophytes of Pteridium aquilinum (L.) Kuhn produced a substance that caused other, newly germinated gametophytes of this species to produce antheridia precociously and abundantly, with a subsequent delay in the formation of a meristematic notch and archegonial production. Since that time, the action, expression, and biochemical structure of this type of compound have been studied in some detail (for reviews see Voeller, 1964; Naf et al., 1975). Subsequent research has also demonstrated that three biochemically distinct general classes of antheridiogens are produced by taxonomically diverse species, best identified trivially by the capital letters A, B, and C, to denote biologically interreactive groupings (Schedlbauer and Klekowski, 1972; Haufler and Gastony, 1978). Antheridiogen A, first isolated from P. aquilinum (Dopp, 1950), affects gametangial development in gametophytes of some members of such diverse families as Blechnaceae, Cyatheaceae, Davalliaceae, Dennstaedtiaceae, Dicksoniaceae, Dryopteridaceae, Polypodiaceae, Pteridaceae, and Thelypteridaceae (all sensu Tryon and Tryon, 1982) (Naf et al., 1975; Voeller, 1964). Antheridiogen B, first demonstrated in Anemia phyllitidis (L.) Sw. (Naf, 1959), affects several species of Schizaeaceae. Antheridiogen C is specific to Ceratopteris (Pteridaceae; Schedlbauer and Klekowski 1972). Fern species tested for antheridiogen response were reviewed by Naf et al. (1975), with subsequent additions by Schedlbauer and Klekowski (1972), Haufler and Gastony (1978), and Haufler and Ranker (1985). Antheridiogens have been implicated as functioning in nature to promote outcrossing in pteridophytes by mediating obligate cross-fertilization through ontogenetic control of gametangial formation in natural gametophyte populations (see Schneller et al., 1990, for review). Previous studies have emphasized two different approaches to the elucidation of antheridiogen function in ferns. As noted above, several studies have documented the susceptibility of gametophytes of various species to antheridiogens of classical producers, as well as the production of native antheridiogens by many of these same species under laboratory culture conditions. These studies have involved exogenous hormonal application by germination of spores on antheridiogen-enriched nutrient agar. Other studies have characterized populations of gametophytes in the field to demonstrate that naturally occurring gametophytes of some temperate and tropical pteridophytes do exist as unisexual plants, as would be predicted if an antheridiogen system were operative in nature (Tryon and Vitale, 1977; Schneller, 1979; Farrar and Gooch, 1975). There have not been any studies to confirm directly the action of an antheridiogen system in nature and problems of experimental design and adequate controls may be insurmountable in this regard. However, recent studies have suggested the existence of an antheridiogen system