Sexual and Apogamous Species of Woodferns Show Different Protein and Phytohormone Profiles

The gametophyte of ferns reproduces either by sexual or asexual means. In the latter, apogamy represents a peculiar case of apomixis, in which an embryo is formed from somatic cells. A proteomic and physiological approach was applied to the apogamous fern Dryopteris affinis ssp. affinis and its sexual relative D. oreades. The proteomic analysis compared apogamous vs. female gametophytes, whereas the phytohormone study included, in addition to females, three apogamous stages (filamentous, spatulate, and cordate). The proteomic profiles revealed a total of 879 proteins and, after annotation, different regulation was found in 206 proteins of D. affinis and 166 of its sexual counterpart. The proteins upregulated in D. affinis are mostly associated to protein metabolism (including folding, transport, and proteolysis), ribosome biogenesis, gene expression and translation, while in the sexual counterpart, they account largely for starch and sucrose metabolism, generation of energy and photosynthesis. Likewise, ultra-performance liquid chromatography-tandem spectrometry (UHPLC-MS/MS) was used to assess the levels of indol-3-acetic acid (IAA); the cytokinins: 6-benzylaminopurine (BA), trans-Zeatine (Z), trans-Zeatin riboside (ZR), dyhidrozeatine (DHZ), dyhidrozeatin riboside (DHZR), isopentenyl adenine (iP), isopentenyl adenosine (iPR), abscisic acid (ABA), the gibberellins GA3 and GA4, salicylic acid (SA), and the brassinosteroids: brassinolide (BL) and castasterone (CS). IAA, the cytokinins Z, ZR, iPR, the gibberellin GA4, the brassinosteoids castasterone, and ABA accumulated more in the sexual gametophyte than in the apogamous one. When comparing the three apogamous stages, BA and SA peaked in filamentous, GA3 and BL in spatulate and DHRZ in cordate gametophytes. The results point to the existence of large metabolic differences between apogamous and sexual gametophytes, and invite to consider the fern gametophyte as a good experimental system to deepen our understanding of plant reproduction.

Hymenasplenium volubile: documentation of its gametophytes and the first record of a hemiepiphyte in the Aspleniaceae

Background and Aims Through careful field examination of the growth habit of the gametophytes and sporophytes of Hymenasplenium volubile across an ontogenetic series, we aim to understand better the evolution of epiphytism in this poorly understood group of ferns Methods We made field observations of H. volubile sporophytes and gametophytes, and brought specimens back to the lab for microscopic analysis. In the field, sporophytes at each ontogenetic stage were photographed to document the species’ growth habit. We used an existing phylogeny to optimize growth form of New World Hymenasplenium. Key Results Young sporophytes were at first fully epiphytic and produced one or two long feeding roots that extend to the soil where they branch profusely. The feeding roots remain in contact with the soil throughout the life of the plant. Thus, H. volubile is a hemiepiphyte. While immature, gametophytes are appressed to the tree trunk, but, as their gametangia mature, their lower margin lifts upward, imparting a shelf-like appearance to the thallus. The thallus attaches to the substrate by branched rhizoids produced along the margin of the thallus in contact with the substrate. Conclusions Hemiepiphytes are a key link in the evolution of epiphytic ferns and may act as a bridge between the forest floor and the canopy. Our finding is the first report of hemiepiphytism in Aspleniaceae, a large lineage with many epiphytic and terrestrial taxa. This work serves as an important model to understand the evolution of epiphytism in this group specifically and in ferns in general. The majority of our understanding of fern gametophyte biology is derived from laboratory studies. Our efforts represent a fundamental contribution to understanding fern gametophyte ecology in a field setting.

Comparative analysis of the sexual phase of Phanerophlebia (Dryopteridaceae) in Mexico

A comparative analysis is presented of the spore morphology, germination pattern, and prothallial development of the sexual phase of seven species in the fern genus Phanerophlebia C. Presl. Gametophyte development was studied from samples grown both on agar and soil. Spores are monolete, ellipsoid, with light brown to dark brown perine; the germination pattern is Vittaria-type and the prothallial development is Aspidium-type in all of the species. The gametangia are of the type typical for leptosporangiate ferns. Gametophytes of all species initially become female, then bisexual. Differences among species include spore germination time (6–12 days), shape of the gametophytes (spatulate–cordiform to cordiform–reniform, with smooth to very irregular margins), development time of trichomes (12–24 days), and appearance of gametangia (40–200 days). Some species develop the first leaves of the sporophytes after 200 days. Results are contrasted with previously published reports on gametophyte development in Arachniodes Blume, Cyrtomium C. Presl, Didymochlaena Desv., Dryopteris Adans, Olfersia Raddi, Polystichum Roth, and Stigmatopteris C. Chr.Key words: Dryopteridaceae, fern gametophyte, Mexico, morphogenesis, Phanerophlebia, sexual phase.

Gametophyte morphology and reproductive biology in Elaphoglossum

Gametophyte morphology, behavior, and growth habit of Elaphoglossum alatum Gaud., Elaphoglossum callifolium (Bl.) Moore, Elaphoglossum crassifolium (Gaud.) Anderson & Crosby, Elaphoglossum marginatum (Wall ex Fee) Moore, and Elaphoglossum yoshinage (Yatabe) Makino were observed on artificial agar medium. The morphology of these gametophytes are very different from those of Bolbitis, a genus of Lomariopsidaecae thought to have a close relationship with Elaphoglossum. The growth habit of Elaphoglossum gametophytes, like many other epiphytic species, is perennial and clone forming. Isozyme analysis of naturally occurring sporophytes of E. alatum, E. crassifolium, and Elaphoglossum paleaceum (Hook. & Grev.) Sledge suggest that sporophytes of E. alatum and E. crassifolium are diploid and derived from highly outbreeding populations. Fixed heterozygosity in E. paleaceum suggests that sporophytes of this species are polyploid, but at least some outcrossing occurs. High genetic loads determined from single gametophyte cultures of E. callifolium and E. crassifolium indicate low probabilities of successful intragametophytic selfing. Several tests indicate, however, that these species neither produce nor respond to antheridiogens. Therefore, intergametophytic mating in these species is likely maintained by genetic load. This mating behavior is promoted by a perennial and clone-forming growth habit which may function to prolong the life-span and to enlarge the space occupied by individual gametophytes.Key words: Elaphoglossum, fern gametophyte, reproductive biology, breeding system.