Student Theses and Dissertations

Date of Award

1969

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Abstract

Many fern spores require light for germination. In one family of ferns, the Schizaeaceae, the gibberellins overcome this light requirement and induce dark-germination. Fern gametophytes produce antheridium-inducing substances. The Anemia substance, antheridogen-B, is demonstrated to induce germination in two genera of the Schizaeaceae, Anemia and Mohria.

The Pteridium substance, antheridogen-A, stimulates germination of at least ten species in two families of ferns, but is not active on species of the Schizaeaceae. In almost all tested cases the antheridogens are active in inducing germination in the same species on which they also induce antheridia. The hormone-induced dark-germination in Anemia phyllitidis (L.) Swartz is pH-dependent while the light-induced germination is insensitive to changes in pH from 3.5 to 7.0.

Light most probably initiates germination in A. phyllitidis by inducing the synthesis of gibberellin-like substances within the spore. The inhibitor of gibberellin biosynthesis, AM0-1618, greatly depresses light-induced germination without affecting gibberellin-induced dark-germination. Gibberellin-like substances, resembling GA 1, 3 and GA 9, are shown to be produced during light-induced germination in quantities of 6 x –10 -9 to 10-7 gram equivalents GA 3 per gram of spores. Synergism between GA 3 and light is observed only under certain conditions and may be explained by a light stimulation of spore permeability.

The two antheridogens and the gibberellin-like material produced by the germinating spore of A. phyllitidis are different substances. The antheridogens also are not identical to any of the known gibberellins.

Cycloheximide inhibits the gibberellin-induced germination and also inhibits incorporation of C 14-amino acids into TCA-insoluble material. Actinomycin D has no effect on germination, but it is not shown whether the inhibitor enters the dormant spore.

Rupture of the spore wall in A. phyllitidis only occurs after a germination stimulus is applied. However, the opening of the spore wall can occur without growth of the spore cell in cycloheximide, 5-fluoro-uracil, or mannitol are applied under certain conditions.

The following sequence of events is hypothesized in the course of the natural germination of A. phyllitidis spores: a) light induces synthesis of gibberellin-like substances, b) gibberellin-like factors initiate the synthesis of specific hydrolases, c) the spore wall is weakened, d) the spore cell extends out from the spore coat.

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