Sexual behaviour of the genus Equisetum, subgenus Equisetum

Gametophytes of five species of Equisetum that were studied in axenic single spore cultures are initially male or female, and the first antheridia appear on the males before the first arche-gonia on the females. The males never produce archegonia, but the females all produce antheridia later in progressively increasing numbers. The proportions of male and bisexual gametophytes are relatively constant within each species but vary greatly between species. Likewise between species there is great variation in the rate at which females later produce antheridia. Male gametophytes are smaller and grow more slowly than females, but individuals of both sexes live for the same length of time. After prolonged culture, growth rates fall to very low levels and there is necrosis of the older parts of the gametophytes; but sex organs are still produced. Initially female gametophytes have much sexually uncommitted tissue, whereas males are composed almost entirely of antheridial branches. The absence of archegonium formation on males may well be related to this lack of sexually undifferentiated tissue and the fact that the growth of the males is intimately connected with antheridium production.     

Gametophyte morphology and gametangial ontogeny of Asplenium foreziense and related taxa (Aspleniaceae: Pteridophyta)

Gametophytes of Asplenium foreziense and related taxa have been studied by culture of spores on mineral agar and soil. Those of A. obovatum ssp. obovatum var. protobillotii and var. deltoideum , ssp. numidicum , and of A. macedonicum are described for the first time. Gametophyte development follows the Adiantum type in the A. obovatum group, and the Aspidium type in A. fontanum . Both types of development have been found in A. foreziense , depending on the sporophytic sample. The taxa with hairy gametophytes show significant differences in hair density. As in most of the homosporous ferns, antheridia are formed first and in a high proportion of gametophytes in the A. obovatum group and in A. fontanum , except for one sample; most of these male gametophytes become bisexual. In A. foreziense and A. macedonicum archegonia are formed first or at the same time as antheridia, but the proportion of female gametophytes is higher than in the other taxa; some of the gametophytes become bisexual, most of them differentiated from the female ones. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 139 , 87–98.     

<Emphasis Type="Italic">In vitro</Emphasis> culture of <Emphasis Type="Italic">Drynaria fortunei</Emphasis>, a fern species source of Chinese medicine “Gu-Sui-Bu”

This study reports spore germination, early gametophyte development and change in the reproductive phase of Drynaria fortunei, a medicinal fern, in response to changes in pH and light spectra. Germination of D. fortunei spores occurred on a wide range of pH from 3.7 to 9.7. The highest germination (63.3%) occurred on ½ strength Murashige and Skoog basal medium supplemented with 2% sucrose at pH 7.7 under white light condition. Among the different light spectra tested, red, far-red, blue, and white light resulted in 71.3, 42.3, 52.7, and 71.0% spore germination, respectively. There were no morphological differences among gametophytes grown under white and blue light. Elongated or filamentous but multiseriate gametophytes developed under red light, whereas under far-red light gametophytes grew as uniseriate filaments consisting of mostly elongated cells. Different light spectra influenced development of antheridia and archegonia in the gametophytes. Gametophytes gave rise to new gametophytes and developed antheridia and archegonia after they were transferred to culture flasks. After these gametophytes were transferred to plastic tray cells with potting mix of tree fern trunk fiber mix (TFTF mix) and peatmoss the highest number of sporophytes was found. Sporophytes grown in pots developed rhizomes.     

Gibberellins and antheridiogen on sex in Blechnum spicant L.

The role of gibberellins (GAs) in determining sex in the gametophyte of the fern Blechnum spicant L. was studied through (a) the effect of exogenous GA₄₊₇ and GA₃ (b) quantitation of the endogenous levels of GA_1, GA₃, GA₄, GA₇, GA₉, and GA₂₀ in male and female gametophytes, and (c) the effect of flurprimidol, a GAs biosynthesis inhibitor of the steps of oxidation of ent-kaureno to ent-kaurenoic acid. Our results show that GA₄₊₇ had a slight effect of inducing either male or female sexual organs, antheridia and archegonia, respectively. The endogenous GAs content was not significantly different between sexes, but the GA₄, GA₇, and GA₂₀ levels were raised above those of the other GAs in both sexes. Neither antheridiogen biosynthesis nor antheridia formation was inhibited by flurprimidol. Gametophytes regenerated from homogenized mature gametophytes (HG) show a different physiological behavior than spore-derived gametophytes. In the first case, gametophytes are males and synthesize antheridiogen before they attain maturity, in contrast to what occurs in spore-derived gametophytes which are females and synthesize antheridiogen when mature.     

Comparative morphology of the gametophytes of Equisetum subgenus Hippochaete and the sexual behaviour of E. ramosissimum subsp. debile, (Roxb.) Hauke, E. hyemale var. affine (Engelm.) A.A., and E. laevigatum A. Br.

Gametophytes of Equisetum , subgenus Hippochaete , species E. hyemale, E. ramosissimum, E. laevigatum, E. variegatum and E. scirpoides are morphologically distinct. Lamellae from female branches and the archegonial neck cells provide a range of diagnostic features but antheridia are uniform throughout this subgenus, unlike the subgenus Equisetum , in which antheridial morphology is the most reliable criterion for specific identification of gametophytes. The classification of Equisetum into two subgenera based on sporophytic features is supported by gametophyte morphology: column lamellae and sunken antheridia with two opercular cells occur in Hippochaete whereas plate lamellae and projecting antheridia prevail in subgenus Equisetum. The absence of well-marked discontinuities in gametophyte morphology in Hippochaete reinforces cytologica! and hybridization data indicating that the taxa are more closely interrelated man in the subgenus Equisetum. No differences in gametophyte morphology were detected at the intraspecific level. Neither gametophyte morphology nor sexuality provide any definitive data to support me theory that Hippochaete contains the most primitive extant horsetails.
Sexuality in E. ramosissimum subsp. debile, E. hyemale var. affine and E. laevigatum is far more labile than in other taxa of Equisetum. Both male and female secondary gametophytes may be derived from initially male or female individuals as a result of lamellar proliferation.     

Sexual behaviour of the genus Equisetum, subgenus Hippochaete

When grown for long periods in axenic single spore cultures, gametophytes of the four European species of subgenus Hippochaete are initially male or female. Females invariably produce antheridia as they get older, but archegonium formation by males is a much rarer event and was only observed in E. hyemale and E. scirpoides. Male gametophytes are smaller, grow more slowly than the females and in E. hyemale and E. variegatum are often short-lived. The proportions of male and bisexual individuals are relatively constant within each species but vary between species. Likewise species differ in the rate at which females later produce antheridia. Gametophytes grow in three ways: activity of antheridial meristems which are totally committed to the formation of male tissues, activity of cushion meristems which may produce archegonia for an indefinite period or switch to antheridium formation, and proliferation from lamellae. Either archegonia or antheridia may arise on the adventitious branches resulting from lamellar proliferation, but the type of sex organ produced is strongly influenced by the culture medium, the sex and age of the parent tissue and the particular species in question. Only by this means are archegonia formed on initially male individuals. The sexual behaviour of the subgenus Hippochaete is compared in some detail with that of the subgenus Equisetum and several subgeneric characteristics are outlined.     

Significance of gametophyte form in long-distance colonization by tropical, epiphytic ferns

Gametophyte morphology of tropical epiphytic ferns may confer an advantage for establishment on islands. Most tropical, epiphytic ferns belong to five families: Hymenophyllaceae, Grammitidaceae, Vittariaceae, Polypodiaceae, and Elaphoglossaceae. Gametophytes of these families are long-lived and clone-forming. In addition, most Hymenophyllaceae, Grammitidaceae, and Vittariaceae produce dispersible gemmae. Each of these characteristics increases opportunity for outbreeding, and when island floras are statistically compared with floras of adjacent mainlands, island floras are found to be rich in epiphytic species possessing gemmae (Hymenophyllaceae, Grammitidaceae, and Vittariaceae), and depauperate in epiphytic species lacking gemmae (Polypodiaceae and Elaphoglossaceae). We propose that gametophytic gemmae significantly aid long-distance colonization of outbreeding species because gemmae 1) allow gametophytes to exploit available niches through dispersal of gemmae, and through clonal expansion and persistence of the resulting gametophyte, and 2) facilitate sexual reproduction by providing the opportunity for sperm and antheridiogen transfer when gametophytes are distant, and by providing a new source of tissue for antheridia formation.     

The Spontaneous Formation of Antheridia in Onoclea is not Blocked by Light

Onoclea sensibilis gametophytes were grown from spores on ashedsoil and agar to determine if the spontaneous formation of antheridiacan be blocked by light. Under most conditions, dark-grown gametophytesformed antheridia later than or at the same time as gametophytesgrown in the light. Under no circumstances was there a rapidonset of maleness in the dark. These results contradict thehypothesis that, in Onoclea, antheridiogen is required to inducemaleness because light inhibits the formation of antheridia.In the light, antheridia formed on heart-shaped thalli. In darkness,antheridia formed on filamentous gametophytes. The timing ofonset of maleness was affected by temperature and the presenceof sucrose. The effect of sucrose on the comparison betweenlight and dark treatments depended on both substrate and temperature Onoclea sensibilis, L., sensitive fern, fern gametophytes, sexuality, light-induced block     

Antheridiogen,dark spore germination,and outcrossing mechanisms in Bommeria (Adiantaceae)

Isozymic analyses of the patterns of genetic variability in sporophyte populations have demonstrated that most fern species have outcrossing breeding systems. However, because fertilization takes place during the ephemeral, diminutive gametophyte generation, direct observation of breeding systems in nature has not been possible. Recent discoveries of soil-bound spore banks suggested that genetic diversity could be stored beneath the surface and subsequently released by appropriate chemical cues. Previous studies demonstrated that Bommeria sporophytes are the product of outcrossing, that their gametophytes carry high levels of genetic load, and that they produce and respond to antheridiogen. Research reported here demonstrated that Bommeria spores can survive long-term storage but will not germinate in the dark. Antheridiogen, however, will release spores from this light requirement and stimulate germination. Higher concentrations of antheridiogen result in higher germination rates. Gametophytes grown in the dark on antheridiogen-enriched agar form antheridia and release actively swimming sperms. Thus, spores housed beneath the soil surface could remain dormant until stimulated to germinate by antheridiogen secreted by surface-dwelling, archegoniate gametophytes. Sperm released from these subterranean gametophytes could fertilize eggs on the surface. Because spores housed in the soil are likely to be genetically different than those at the surface, heterozygous sporophytes would be more likely to result. Discovering that Bommeria species contain all of the prerequisites for this proposed outcrossing mechanism provides an explanation for the maintenance of genetic diversity in some fern populations.     

Gametophytic phase of Alsophila odonelliana (Cyatheaceae)

The gametophytic morphology and development of Alsophila odonelliana (Alston) Lehnert, have been studied through in vitro cultures. This species grows in southern Bolivia and northwestern Argentina. The spores are uniform in structure, but not in size; a certain percentage being smaller than the average. 16 spores per sporangium were found. The germination is of the Cyathea type. It was found that spores stored at 4°C can maintain their viability for over two years. The maximum value of germination depends on spore age. The filamentous gametophytes are 4–16 cells long. Young gametophytes have 1–2 branches that give rise to new gametophytes. Male, female, bisexual and neuter gametophytes were found. Propagules were frequently found in neuter gametophytes, and female and bisexual gametophytes were found to have chlorophyll containing scales. The antheridia are made up of five cells and produce non‐viable spermatozoids. The archegonia have necks formed by four columns with four cells each. Most of the gametophytic phase is documented with photomicrographs.     

Cell number,cell growth,antheridiogenesis, and callose amount is reduced and atrophy induced by deoxyglucose in <Emphasis Type="Italic">Anemia phyllitidis</Emphasis> gametophytes

Fluorescence staining and morphometrical measurements revealed that callose was a component of newly formed cell plates of symmetrically dividing cells and asymmetrically dividing antheridial mother cells during gibberellic acid-induced antheridiogenesis as well as in walls of young growing cells of Anemia phyllitidis gametophytes. Callose in cell walls forms granulations characteristic of pit fields with plasmodesmata. 2-deoxy-d-glucose (DDG), eliminated callose granulations and reduced its amount estimated by measurements of fluorescence intensity. This effect was accompanied by reduction of antheridia and cell numbers as well as size and atrophy of particular cells and whole gametophytes. It is suggested that inhibition of glucose metabolism and/or signalling, might decrease callose synthesis in A. phyllitidis gametophytes leading to its elimination from cell plates of dividing cells and from walls of differentiating ones as well as from plasmodesmata resulting in inhibition of cytokinesis, cell growth and disruption of the intercellular communication system, thus disturbing developmental programs and leading to cell death.     

Environmental Influences on Kelp Performance across the Reproductive Period: An Ecological Trade-Off between Gametophyte Survival and Growth?

Most kelps (order Laminariales) exhibit distinct temporal patterns in zoospore production, gametogenesis and gametophyte reproduction. Natural fluctuations in ambient environmental conditions influence the intrinsic characteristics of gametes, which define their ability to tolerate varied conditions. The aim of this work was to document seasonal patterns in reproduction and gametophyte growth and survival of Ecklonia radiata (C. Agardh) J. Agardh in south-western Australia. These results were related to patterns in local environmental conditions in an attempt to ascertain which factors explain variation throughout the season. E. radiata was fertile (produced zoospores) for three and a half months over summer and autumn. Every two weeks during this time, gametophytes were grown in a range of temperatures (16–22°C) in the laboratory. Zoospore densities were highly variable among sample periods; however, zoospores released early in the season produced gametophytes which had greater rates of growth and survival, and these rates declined towards the end of the reproductive season. Growth rates of gametophytes were positively related to day length, with the fastest growing recruits released when the days were longest. Gametophytes consistently survived best in the lowest temperature (16°C), yet exhibited optimum growth in higher culture temperatures (20–22°C). These results suggest that E. radiata releases gametes when conditions are favourable for growth, and E. radiata gametophytes are tolerant of the range of temperatures observed at this location. E. radiata releases the healthiest gametophytes when day length and temperature conditions are optimal for better germination, growth, and sporophyte production, perhaps as a mechanism to help compete against other species for space and other resources.     

UNUSUAL DARK-GROWTH AND ANTHERIDIAL DIFFERENTIATION IN SOME GAMETOPHYTES OF THE FERN ONOCLEA SENSIBILIS

A fertile frond of O. sensibitis was found which yielded spores with unusual growth characteristics. About 25% of the gametophytes derived from the spores were able to undergo 2-dimensional development in darkness, in contrast to normal plants which are filamentous in darkness. When the aberrant spores were cultured in darkness under conditions of reduced ethylene concentration, the proportion of 2-dimensional plants rose to 75%, and, moreover, up to 50% of the gametophytes produced antheridia within 2 weeks. Under comparable conditions normal gametophytes produced no antheridia. The medium from antheridial cultures of the aberrant spores failed to induce the formation of antheridia in other plants.     

Photosynthetic response to light and temperature in Laminaria digitata gametophytes from two French populations

Given the growing body of evidence on the general decline of kelp beds worldwide, it is crucial to understand the physiological responses of kelp gametophyte stages to environmental parameters. We investigated the physiological responses to light and temperature of gametophytes from two populations of Laminaria digitata in contrasting environments along the French coast of the English Channel. Gametophytes of both populations were highly tolerant of high light through an efficient down-regulation of photosynthesis triggered by the activation of the xanthophyll cycle. Temperature increases promoted photosynthesis and photosystem II showed high resistance to short-term exposure to high temperatures currently encountered in the field. Gametophytes from the two sites displayed some differences in their pigment content and photosynthetic characteristics, but low replication and difference in time of sampling precluded tests of potential local adaptation to the light conditions at each site, as observed in previously published results on adult sporophytes. Gametophytes of L. digitata appeared to be resistant to irradiation and temperature conditions currently experienced in the field, confirming their role in persistence of kelp species under stressful environmental conditions.     

INTERGENERIC HYBRIDIZATION AMONG FIVE GENERA OF THE FAMILY LESSONIACEAE (PHAEOPHYCEAE) AND EVIDENCE FOR POLYPLOIDY IN A FERTILE PELAGOPHYCUS×MACROCYSTIS HYBRID

Hybridization was attempted by combining gametophytes between intergeneric pairs among the following taxa in the Lessoniaceae: Macrocystis pyrifera ( L.) C. Agardh , M. integrifolia Bory, M. angustifolia Bory , Pelagophycus porra ( Leman) Setch ., Nereocystis luetkeana ( Mert.) Post & Rupr ., Dictyoneurum californicum Rupr ., and Dictyoneuropsis reticulata ( Saud.) Smith. Hybrid sporophytes were produced in some combinations involving Macrocystis × Pelagophycus and Macrocystis × Dictyoneurum, and in all combinations of Dictyoneuropsis × Dictyoneurum. This is the first report of intergeneric hybrids involving Dictyoneurum. Gametophytes of P. porra had 16–24 chromosomes. Gametophytes from a fertile Macrocystis-Pelagophycus hybrid were crossed with Macrocystis and Pelagophycus gametophytes. Hybrid male gametophytes and Pelagophycus female gametophytes produced sporophyte progeny, but hybrid males with Macrocystis females did not. A single hybrid female gametophyte did not produce gametophytes in combination with hybrid males , Pelagophycus males or Macrocystis males. The hybrid gametophytes had approximately 30 chromosomes. It is hypothesized that the hybrid is an alloploid, containing a complete set of Macrocystis and Pelagophycus chromosomes, which may have allowed meiosis and sporogenesis to proceed normally in the hybrid sporophyte found in the sea. Thus, reproductive isolating mechanisms appear to operate at both pre- and postzygotic stages, and both can be overcome in intergeneric hybrids .     

Culture studies on the life history of Haplospora globosa and Tilopteris mertensii (tilopteridales,phaeophyceae)

The complete life histories of Tilopteris mertensii and haplospora globosa were followed in culture. Tilopteris shows a succession of identical plants through uninucleate “eggs” which develop parthenogenetically. In Haplospora, sporophytes alternate with gametophytes without sexuality and nuclear alternation. However, evidence for meiotic stages is found in sporangium initials. Gametophytes produce oogonia and antheridia, and eggs develop parthenogenetically. The chromosome number of Tilopteris is n = 62 (60–65). In both phases of Haplospora numbers are n = 50 (43–54). Haplospora from Heligoland perpetuates the sporophyte only at chromosome numbers of n = 25 (22–28).     

Phenology and wintering capacity of sporophytes and gametophytes of ferns native to northern Japan

Summary To investigate life history adaptations to cold climates, the leaf development, sporulation period, growing stage of gametophytes, and the frost and drought resistance of sporophytes and gametophytes of 67 fern species native to Kokkaido were studied. Most ferns common in Hokkaido are summer-green with leaves developing during late May to June and decaying during October. Most of the ferns in Hokkaido sporulate during August to early September. Spores dispersed from June to September germinate before winter begins, forming vegetative prothallia. Gametophytes mature only in the following summer. Thus in Hokkaido the gametophytes as well as perennial sporophytes are exposed to severe winter conditions. In order to correlate the life cycles of temperate ferns with winter cold stress, frost resistance of gametophytes, rhizomes, and leaves of sporophytes were determined. Maximal frost resistance of rhizomes reflects the stress conditions of their habitats: rhizomes of forest understory ferns are damaged at-5°to -17.5°C, epiphytic ferns and ferns of habitats exposed to severe frost sustained temperatures of -20° to-40°C. The leaves of winter-green and evergreen ferns resist frost ranging from -25° to -40°C. The leaves of summer-green ferns are killed by late frost below -5°C. With some exceptions, gametophytes of ferns growing on the forest floor resist frost to -40°C and are much hardier than sporophytes. These results suggest the possible restrictive effects of cold climate on the life span of leaves as well as on the sporulation period. If winter cold is one of the decisive factors for seasonality expression and habitat distribution of ferns, the sensitive generation must be the sporophyte rather than the gametophyte. The hardier gametophyte is therefore able to colonize habitats in which the sporophyte is excluded by frost if mechanisms of vegetative propagation are evolved.Contribution No. 2451 from The Institute of Low Temperature Science     

ACTION OF PURINE AND PYRIMIDINE ANALOGS ON THE GROWTH AND DIFFERENTIATION OF THE GAMETOPHYTES OF THE FERN ASPLENIUM NIDUS

The purine analogs, 8-azaadenine, 8-azaguanine, 8-azaxanthine and 8-azahypoxanthine, and the pyrimidine analogs, 2-thiocytosine, 5-fluorouracil, 2-thiouracil and 6-azauracil, inhibited the induction of 2-dimensional growth in the gametophytes of the fern Asplenium nidus L. In contrast, thymine analogs such as 5-fluorodeoxyuridine, 2-thiothymine, 6-azathymine and 5-bromouracil caused non-specific growth inhibitions without suppressing 2-dimensional growth. Subinhibitory concentrations of 8-azaxanthine, 8-azahypoxanthine, and 2-thiouracil promoted both 1-dimensional and 2-dimensional phases of growth of the gametophytes. Inhibitory effects of the analogs were observed on treatment of the spores or of gametophytes of different ages. Gametophytes growing in the analogs for different periods of time recovered from inhibition on transfer to the basal medium.     

The effects of methionine and cobalt ions on sex expression and development of <Emphasis Type="Italic">Anemia phyllitidis</Emphasis> gametophytes

One of the prime precursor for ethylene synthesis — L-methionine and the inhibitor of 1-aminocyclopropane-1-carboxylic acid oxidase (ACO) — Co²⁺-were tested for their effects on sex expression and development of Anemia phyllitidis fern gametophytes. Five concentrations of both chemicals (0, 10, 25, 50, 100 μM) were analysed with reference to antheridia and archegonia formation, number and size of cells as well as thalli length using the three-zone model of gametophyte structure. Both substances, however at different concentrations, enhanced the number of GA₃-induced antheridia and similarly stimulated the cell number and inhibited thalli length. Both of them at 100 μM concentrations without GA₃ induced meristematic area formation while methionine also induced archegonia in the apical parts of gametophytes. These findings correspond with the previous observations concerning the important role of ethylene synthesis precursor (ACC) in controlling gibberellic acid-induced male sex expression in ferns and broaden the knowledge about the mechanisms of fern gametophyte development.     

Effect of temperature on the development of Saccharina japonica gametophytes

Spores (collected at 10?±?1 °C, 2 h after releasing) and young gametophytes (newly generated from spores cultured at 10?±?1 °C for 8 days) of Saccharina japonica were first cultured at 15?±?1, 19?±?1, and 23?±?1 °C for various times (2, 5, and 8 days) and then at 10?±?1 °C (culturing patterns S and G, respectively). Spores were also cultured at a constant of 10?±?1 °C (pattern C) and used as the control. The length and percentage of young gametophytes, size and percentage of gametophytes, and ratio of female to male gametophytes were measured in order to determine the effect of temperature on the development of gametophytes. Temperature and exposure time of spores and young gametophytes at the first culturing temperature significantly affected the development of gametophytes as were indicated by all biological parameters except the ratio of female to male gametophytes. The spores were more sensitive to temperature than young gametophytes. Gametophytes developed from the spores that survived temperature stress can recover their growth. High temperature selection at the early developmental stages of gametophytes was effective for screening gametophytes applicable for breeding high temperature-resistant varieties and hybrids.