Gametophyte contribution to sporophyte growth on the basis of carbon gain in the fern <Emphasis Type="Italic">Thelypteris palustris</Emphasis>: effect of gametophyte organic-matter production on sporophytes

At an early stage of growth gametophytes support the sporophytes of ferns. Young sporophytes become independent of gametophytes when the first leaves develop. Although large fern gametophytes produce multiple archegonia simultaneously, only one sporophyte is typically established on one gametophyte. The number of sporophytes is believed to be controlled in two possible directions, from gametophyte to sporophyte or from preceding sporophyte to another sporophyte. To investigate the effects of gametophytes on their sporophytes, we studied the relationship between organic matter production by gametophytes and the growth of young sporophytes of Thelypteris palustris. We cut gametophytes in half (CGs) to reduce the gametophytes’ production of matter. There was no significant difference between the growth of sporophytes on intact gametophytes (IGs) and that on CGs. According to our estimates, based on the rate of organic matter production, the large gametophyte was able to produce two or more sporophytes. The resources required for CGs to make similar-sized sporophytes was twice that for IGs. In polyembryony each of the multiple sporophytes was similar in size to the single sporophytes. Resource limitation does not seem to explain why fern gametophytes establish single sporophytes.     

Growth and reproductive characteristics in artificially formed clonal gametophytes ofDryopteris filix-mas (Dryopteridaceae)

Artificially formed clonal gametophytes ofDryopteris filix-mas (L.)Schott were able to grow and reproduce, although growth rates, proportions of hermaphrodites and reproductive efforts were low. Variable density and nutrient levels appeared to affect gametophytic life histories and they continued to influence the viability of the developing sporophyte generation. Differences between populations and sporophytes were discovered in life histories. Hermaphroditic gametophytes were considerably larger and possessed higher viability than did males. Clear differences between clones in the level of phenotypic plasticity in gametophyte size were observed. No neighbor effect on gametophyte sex expression was detected with the densities and nutrient levels used.     

How was apical growth regulated in the ancestral land plant? Insights from the development of non-seed plants

Land plant life cycles are separated into distinct haploid gametophyte and diploid sporophyte stages. Indeterminate apical growth evolved independently in bryophyte (moss, liverwort, and hornwort) and fern gametophytes, and tracheophyte (vascular plant) sporophytes. The extent to which apical growth in tracheophytes co-opted conserved gametophytic gene networks, or exploited ancestral sporophytic networks, is a long-standing question in plant evolution. The recent phylogenetic confirmation of bryophytes and tracheophytes as sister groups has led to a reassessment of the nature of the ancestral land plant. Here, we review developmental genetic studies of apical regulators and speculate on their likely evolutionary history.

The combined results of recent developmental genetics and phylogenetics studies suggest that the ancestral sporophyte was more complex than previously thought.     

OBLIGATE OUTCROSSING IN A HOMOSPOROUS FERN: FIELD CONFIRMATION OF A LABORATORY PREDICTION

While homosporous ferns are potentially capable of producing totally homozygous sporophytes in one generation via selfing of their bisexual gametophytes, laboratory analyses indicate that a variety of mechanisms promote gametophytic outcrossing. The operation of these mechanisms in natural sporophyte populations, however, has not been previously demonstrated. Laboratory analyses of gametophyte ontogeny show that Bommeria hispida is obligately outcrossing. Electrophoretic data presented here indicate that individuals from natural sporophyte populations of this species are highly heterozygous. Electrophoretic data, therefore, corroborate evidence from the in vitro analysis of gametophyte development and demonstrate that sporophytes of B. hispida in nature typically are products of outcrossing between genetically different gametophytes. Extrapolations from the literature, together with our findings, indicate that outcrossing mechanisms may operate frequently in ferns, thereby maintaining genetic variability between individuals within populations. This evidence questions whether most ferns are highly inbred and therefore predominantly homozygous.     

Filial mistletoes: the functional morphology of moss sporophytes

Background

A moss sporophyte inherits a haploid set of genes from the maternal gametophyte to which it is attached and another haploid set of genes from a paternal gametophyte. Evolutionary conflict is expected between genes of maternal and paternal origin that will be expressed as adaptations of sporophytes to extract additional resources from maternal gametophytes and adaptations of maternal gametophytes to restrain sporophytic demands.

Interpretation

The seta and stomata of peristomate mosses are interpreted as sporophytic devices for increasing nutrient transfer. The seta connects the foot, where nutrients are absorbed, to the developing capsule, where nutrients are needed for sporogenesis. Its elongation lifts stomata of the apophysis above the boundary layer, into the zone of turbulent air, thereby increasing the transpirational pull that draws nutrients across the haustorial foot. The calyptra is interpreted as a gametophytic device to reduce sporophytic demands. The calyptra fits tightly over the intercalary meristem of the sporophytic apex and prevents lateral expansion of the meristem. While intact, the calyptra delays the onset of transpiration.

Predictions

Nutrient transfer across the foot, stomatal number and stomatal aperture are predicted to be particular arenas of conflict between sporophytes and maternal gametophytes, and between maternal and paternal genomes of sporophytes.     

Contribution of fern gametophytes to the growth of produced sporophytes on the basis of carbon gain

Sporophytes appeared on most gametophytes of Thelypteris palustris (Salisb.) Schott that reached a certain size, which is interpreted to be a critical size of gametophytes for the production of sporophytes. After sporophytes were produced, attached gametophytes ceased dry weight growth, but the gametophytes which did not produce sporophytes grew successively. It was hypothesized that matter produced by gametophytes was being supplied to young sporophytes. Photosynthesis and respiration of gametophytes with attached sporophytes were not significantly different from that of gametophytes without sporophytes. Photosynthetic activity of gametophytes dropped from 0.18 to 0.03 mol CO₂ g^–1 s^–1 during the growth period. The higher photosynthetic rates of gametophytes in the early growth stage were important for reaching the critical size for sporophyte production in a short time. Sporophytes in the one leaf stage averaged 0.14 mol CO₂ g^–1 s^–1 of photosynthetic activity. The results show that sporophytes that had expanded the first leaf grow by their own photosynthetic production. Gametophytes allocated the photosynthate for sporophytes and it was an important aid before the one-leaf stage. The supportive role of gametophytes ended at that stage.     

The evolution of root hairs and rhizoids

Background

Almost all land plants develop tip-growing filamentous cells at the interface between the plant and substrate (the soil). Root hairs form on the surface of roots of sporophytes (the multicellular diploid phase of the life cycle) in vascular plants. Rhizoids develop on the free-living gametophytes of vascular and non-vascular plants and on both gametophytes and sporophytes of the extinct rhyniophytes. Extant lycophytes (clubmosses and quillworts) and monilophytes (ferns and horsetails) develop both free-living gametophytes and free-living sporophytes. These gametophytes and sporophytes grow in close contact with the soil and develop rhizoids and root hairs, respectively.

Scope

Here we review the development and function of rhizoids and root hairs in extant groups of land plants. Root hairs are important for the uptake of nutrients with limited mobility in the soil such as phosphate. Rhizoids have a variety of functions including water transport and adhesion to surfaces in some mosses and liverworts.

Conclusions

A similar gene regulatory network controls the development of rhizoids in moss gametophytes and root hairs on the roots of vascular plant sporophytes. It is likely that this gene regulatory network first operated in the gametophyte of the earliest land plants. We propose that later it functioned in sporophytes as the diploid phase evolved a free-living habit and developed an interface with the soil. This transference of gene function from gametophyte to sporophyte could provide a mechanism that, at least in part, explains the increase in morphological diversity of sporophytes that occurred during the radiation of land plants in the Devonian Period.     

安徽大龙山国家森林公园东亚小金发藓配子体与孢子体个体性状及其相互关系

植物性状是植物对环境变化响应和适应的综合反映。目前对苔藓植物个体水平功能性状的研究较为匮乏。以安徽大龙山国家森林公园分布的东亚小金发藓（Pogonatum inflexum）雌株为例,在其孢子体成熟期测定地上部分孢子体和配子体的形态特征及生物量,系统分析了植株性状变异特征、异速生长关系及协变（整合）格局。结果表明,东亚小金发藓配子体形态性状变异性高于孢子体,且二者生物量变异系数最大。孢子体高度是配子体的2倍,但其生物量仅占地上部分的23%。孢子体和配子体功能性状之间有一定相关性;形态性状（Y）与生物量（X）之间多为指数<1.0异速生长关系,而孢子体和配子体生物量之间为等速生长关系（指数为1.135±0.158）。孢子体生物量分配比例随个体增大而显著减小,体现出显著的负的个体大小依赖。主成分分析表明,东亚小金发藓孢子体和配子体主要个体性状具有不同的协变方向（即两个不同的性状群）,其中孢子体生物量是两类性状群的关键结点。综合来看,东亚小金发藓个体性状间具有与维管植物相似的协变关系。     

RADIOACTIVE TRACER STUDY OF SPOROPHYTE NUTRITION IN HEPATICS

Sporophytes of Fossombronia foveolata, Lophocolea heterophylla, Pellia epiphylla, Ptilidium pulcherrimum, and Riella affinis were surgically isolated from host gametophyte tissues and treated with ¹⁴CO₂. Sporophytes of all five species are capable of fixing CO₂ in the light. Sporophyte/gametophyte ratios for ¹⁴CO₂ fixation/mg fresh weight range between 0.12 and 0.39. Corresponding ratios for chlorophyll content are 1.07 to 3.30. Of the total ¹⁴CO₂ fixed by excised Lophocolea sporophytes, 40% can be attributed to the photosynthetic activity of haploid spores. Enveloping gametophytic tissues (calyptra and pseudoperianth) inhibit photosynthesis of attached sporophytes by as much as 50%. For sustained growth, sporophytes rely on organic nutrients supplied by the gametophyte: radioactivity of Lophocolea sporophytes increases significantly after application of ¹⁴C-glucose to host gametophytes. Surgically isolated sporophytes develop slowly in mineral culture, without significant increase in dry weight. The assumption that hepatic sporophytes are at least partly autonomous with respect to organic nutrition (an assumption that figures prominently in speculation on the evolutionary origin of the sporophyte) is confirmed.     

Selection of a mutation conferring high NaCl tolerance to gametophytes of Ceratopteris

Summary Spores from a weakly salt tolerant strain of Ceratopteris richardii containing the mutation stl1 were irradiated and sown on nutrient medium supplemented with 200 mM NaCl. A single highly salt tolerant gametophyte was recovered and selfed to generate a homozygous sporophyte. Spores from this strain, 1023, were used to document the sexual transmission of the trait and to monitor the inheritance of tolerance in crosses to both the wild type and to the parental salt tolerant strain. Genetic analysis showed the 1023 strain to possess both the original stl1 mutation and an additional semi-dominant nuclear mutation, stl2, that individually conferred a high level of tolerance to gametophytes. In combination, both mutations had additive effects. Tolerance was also evident in sporophytes, but at a lower level than in gametophytes.     

Segregation distortion in Arabidopsis <Emphasis Type="Italic">gametophytic factor 1 </Emphasis>(<Emphasis Type="Italic">gfa1</Emphasis>) mutants is caused by a deficiency of an essential RNA splicing factor

The female and male gametophytes are critical components of the angiosperm life cycle and are essential for the reproductive process. The gametophytes share many essential cellular processes with each other and with the sporophyte generation. As a consequence, these processes can only be analyzed genetically in the gametophyte generation. Here, we report the characterization of the gametophytic factor 1 (gfa1) mutant. The gfa1 mutation exhibits reduced transmission through both the female and male gametophytes. Reduced transmission through the female gametophyte is due to an effect on female gametophyte development. By contrast, development of the pollen grain is not affected in gfa1; rather, reduced transmission is likely due to an effect on pollen tube growth. We have identified multiple T-DNA-insertion alleles of gfa1 in a gene encoding a protein with high similarity to Snu114/U5-116 kD proteins from yeast and animals required for normal pre-mRNA splicing. Consistent with its predicted function, the GFA1 gene (At1g06220) is expressed throughout the plant. Together, these data suggest that GFA1 functions in mRNA splicing during the plant life cycle. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

IAA-induced apogamy in Platycerium coronarium (Koenig) Desv. gametophytes cultured in vitro

Apogamous sporophytes were produced on Platycerium coronarium gametophytes cultured in the presence of indole-3-acetic acid (IAA). The percentage of apogamy as well as the total number of apogamous sporophytes produced per gametophyte clump were highest in the presence of 40 M IAA. When ethylene was allowed to accumulate in the culture vessel in the presence of an optimum level of IAA, the percentage and total number of apogamous sporophyte production decreased significantly. Using light microscope and confocal laser scanning microscope we have shown that nuclear size can be used as a quick parameter to estimate the ploidy level of P. coronarium.Abbreviations CLSM confocal laser scanning microscope - IAA Indole-3-acetic acid - MS Murashige and Skoog     

Changes in Thallus Weight and Size in the Green Alga Ulva fenestrata under Artificial Conditions

From August to October 2002, daily measurements of the thallus weight and area were taken in sporophytes and male and female gametophytes of Ulva fenestrata at similar developmental phases. The algae were reared in aquaria at a constant temperature (22 ± 0.5°C); illumination was applied for 12h a day at a photosynthetically active radiation intensity of 400 E/(m² s). All generations showed a linear increase in the thallus weight and area over time with the same relative daily increment (8 to 15%). Generations differed significantly in time to onset of sporogenesis or gametogenesis. The female gametophyte, sporophyte, and male gametophyte began to release gametes or spores in 7, 10, and 15 days, respectively. A scheme for the distribution of cells among age groups is proposed. The scheme seems to account for the linear pattern of thallus growth.     

Characterisation of complementary DNAs from the expressed sequence tag analysis of life cycle stages of Laminaria digitata (Phaeophyceae)

Laminariales (Phaeophyceae, Heterokonta) are characterised by a heteromorphic digenetic life cycle with a filamentous, microscopic gametophyte and a highly evolved, macroscopic sporophyte. With the ultimate goal of comparing gene expression in each life cycle stage, complementary DNA libraries were constructed from sporophytes and gametophytes of Laminaria digitata. A set of ca. 500 expressed sequence tags (EST) was generated from each life history phase, by single-run partial sequencing of randomly picked cDNA clones. Comparison of the EST deduced amino acid sequences with database protein sequences assigned a putative identity for 39% of the 412 gametophyte clones and 48% of the 493 sporophyte clones sequenced thus far. These data represent more than 152 different proteins now probably identified in L. digitata. Several of those newly identified proteins are of interest to our understanding of the molecular physiology of kelps, for example their carbon-concentrating mechanisms, cell wall biosynthesis and halogen metabolism. EST analysis also confirmed that genes with long 3-UTRs are widespread in Laminariales and the study of 5-UTRs allowed the identification of a Kozak consensus sequence, c(A/C)A(A/C)CAUGGc(G/T). Several potential developmentally regulated differences in gene expression are discussed.     

Comparative glycan profiling of Ceratopteris richardii ‘C-Fern’ gametophytes and sporophytes links cell-wall composition to functional specialization

Background and Aims

Innovations in vegetative and reproductive characters were key factors in the evolutionary history of land plants and most of these transformations, including dramatic changes in life cycle structure and strategy, necessarily involved cell-wall modifications. To provide more insight into the role of cell walls in effecting changes in plant structure and function, and in particular their role in the generation of vascularization, an antibody-based approach was implemented to compare the presence and distribution of cell-wall glycan epitopes between (free-living) gametophytes and sporophytes of Ceratopteris richardii ‘C-Fern’, a widely used model system for ferns.

Methods

Microarrays of sequential diamino-cyclohexane-tetraacetic acid (CDTA) and NaOH extractions of gametophytes, spores and different organs of ‘C-Fern’ sporophytes were probed with glycan-directed monoclonal antibodies. The same probes were employed to investigate the tissue- and cell-specific distribution of glycan epitopes.

Key Results

While monoclonal antibodies against pectic homogalacturonan, mannan and xyloglucan widely labelled gametophytic and sporophytic tissues, xylans were only detected in secondary cell walls of the sporophyte. The LM5 pectic galactan epitope was restricted to sporophytic phloem tissue. Rhizoids and root hairs showed similarities in arabinogalactan protein (AGP) and xyloglucan epitope distribution patterns.

Conclusions

The differences and similarities in glycan cell-wall composition between ‘C-Fern’ gametophytes and sporophytes indicate that the molecular design of cell walls reflects functional specialization rather than genetic origin. Glycan epitopes that were not detected in gametophytes were associated with cell walls of specialized tissues in the sporophyte.     

GENETIC LOAD IN OSMUNDA REGALIS POPULATIONS

Osmunda regalis sporophytes form haploid spores which develop into functionally hermaphroditic gametophytes. The self-fertilization of such gametophytes results in zygotes which are completely homozygous. Spore samples collected from sporophytes in natural populations were used to establish gametophyte cultures. The majority of these gametophytes were unable to form viable embryos when only self-fertilization was possible. Controlled selfing and crossing experiments revealed that the inability of these homozygous embryos to develop normally is attributable to the presence of recessive lethals. To account for this genetic load, an hypothesis is proposed integrating the morphology and ecology of the gametophyte generation with the polyploid genetic system of the sporophyte generation.     

Behavior of nuclei during zoosporogenesis in Bryopsis plumosa (Bryopsidales, Chlorophyta)

The behavior of nuclei during zoosporogenesis in Bryopsis plumosa (Bryopsidales, Chlorophyta) was examined by fluorescence and electron microscopy. Each mature filamentous sporophyte had a single lenticular nucleus, which was about 25 m in diameter and embedded in a thick cytoplasmic layer. At the commencement of multinucleation, giant nuclei with large vacuolated nucleoli, giant nuclei containing chromosomes, and dumbbell-shaped nuclei were observed. Sometimes, two small nuclei also appeared in the thick cytoplasm where the giant nucleus had presumably been present. Electron microscopy revealed the existence of ribbon-like structures resembling synaptonemal complexes within the nucleus having a large vacuolated nucleolus. Nuclei extended their distribution by repetitive divisions. A pair of centrioles was adjacent to the interphase nucleus. When the nuclei were distributed throughout the cell, they became localized nearly equidistantly from one another, each being surrounded by several chloroplasts. At this stage, many centrioles lay along the nuclear surface. The bulk of cytoplasm was then divided into many masses of protoplasm, each of which developed into a uninucleate, stephanokontic zoospore with a whorl of flagella.     

Generating Autotetraploid Sporophytes and Their Use in Analyzing Mutations Affecting Gametophyte Development in the Fern Ceratopteris

The haploid gametophytes of the fern Ceratopteris richardii are autotrophic and develop independently of the diploid sporophyte plant. While haploid genetics is useful for screening and characterizing mutations affecting gametophyte development in Ceratopteris, it is difficult to assess whether a gametophytic mutation is dominant or recessive or to determine allelism by complementation analysis in a haploid organism. This report describes how apospory can be used to produce genetically marked polyploid sporophytes whose gametophyte progeny are heterozygous for mutations affecting sex determination in the gametophyte and a known recessive mutation affecting the phenotype of both the gametophyte and sporophyte. The segregation ratios of wild-type to mutant phenotypes in the gametophyte progeny of polyploid sporophyte plants indicate that all of the mutations examined are recessive. The presence of many multivalents and few univalents in meiotic chromosome preparations of spore mother cells confirm that the sporophyte plants assayed are polyploid. The DNA content of the sperm of their progeny gametophytes was also found to be approximately twice that of sperm from wild-type haploid gametophytes.     

Life history characteristic ofCyrtomium falcatum around the natural northern boundary in Hokkaido,with reference to the alternation of generations

To understand the life history characteristic for expanding the distributional area to colder climates, developmental age structure of population ofCyrtomium falcatum was observed along southwestern coasts of Hokkaido at the natural northern boundary of its distribution, with reference to the alternation of generations. The length and number of pinna of fertile leaves ofCyrtomium falcatum decrease towards the northern part of Japan. In southwestern Hokkaido, typically dwarf fertile leaves and gametophytes were observed growing together on cliffs nearby the sea. To estimate the developmental ages of small and dwarf leaves, the number of venation (NV: branching number of vein from midrib) of leaves was counted on each sporophyte. The sporophyte with leaves at the simple pinna stage ranging from 0–25NV, is predominant in the population of southwestern coasts of Hokkaido. The fertility of the sporophyte seems to be achieved more than five years after the germination. The gametophytes were also observed at the location to be almost equal in number to sporophytes. The number of gametophytes and sporophytes decreases with advancement of developmental stages. In the same location at Okushiri Isl. with slight gradiency of humidity, the gametophyte is predominant on the drier cliff, while the sporophyte is predominant on the humid hole. The population ofCyrtomium falcatum at the natural northern boundary in Hokkaido, seems to have the life history characteristic with alternation of generations. Contribution No. 2557 from the Inst. of Low Temp. Sci.     

Accumulation of Pb and Zn in Gametophytes and Sporophytes of the Moss Funaria hygrometrica(Funariales)

Accumulation of lead and zinc was studied in the moss Funariahygrometrica Hedw. collected from mine tailings. Heavy metalaccumulation in gametophytes and sporophytes was quantifiedby graphite furnace atomic absorption spectrometry (GFAAS) andinductively coupled plasma-atomic emission spectrometry (ICP-AES).Pb and Zn accumulation in the placental zone was analysed byx-ray scanning electron microscopy (SEM) and transmission electronmicroscopy (TEM) microanalysis. Spectrometry showed that whilemoss gametophytes accumulated considerable concentrations ofheavy metals, sporophytes accumulated only small concentrationsof metals. X-ray SEM and TEM showed that the two metals accumulatedin placental transfer cells on both the gametophytic and sporophyticsides. To investigate the uptake pattern for both metals undercontrolled conditions, F. hygrometrica plants collected froma non-polluted site were treated in the laboratory with separatesolutions of Pb and Zn at two concentrations (10^-2and 10^-4 M)for 24 or 168 h. Metal accumulation was analysed separatelyin gametophytes and sporophytes using GFAAS and ICP–AES.Each generation had a different accumulation quotient for bothmetals, and gametophytes accumulated significantly more metalthan sporophytes. Concentrations of Zn in sporophytes were alwayshigher than concentrations of Pb. The findings are discussedin relation to the role performed by the gametophyte and theplacenta in the accumulation and sequestration of Pb and Zn.Copyright 2001 Annals of Botany Company Atomic spectroscopy, Funaria hygrometrica, gametophyte, Pb and Zn accumulation, sporophyte, x-ray TEM and SEM microanalysis