Costs of sporophyte production in the moss,Dicranum polysetum

We investigated the cost of sporophyte production in the moss Dicranum polysetum both by examining patterns of growth and reproduction in unmanipulated shoots and by experimentally manipulating sexual reproduction.The estimated proportion of total carbon investment allocated to sexual reproduction in sporophyte-producing shoots over the study period was 74.8%. Unmanipulated shoots that aborted all sporophytes had a significantly higher growth in the top shoots than shoots that produced sporophytes. In sporophyte-producing shoots, total apical growth decreased proportionately with the number of sporophytes.Experimental prevention of sporophyte development resulted in significantly higher total apical growth of the gametophytes. Shoots where current perichaetia were lacking when marked had a mass increase in the top shoots similar to manipulated sporophytic shoots whereas sporophytic control shoots grew significantly less than these two categories.The difference between control shoots and manipulated shoots in the mass of vegetative apical growth was mainly because of different length increments whereas mass per unit length was similar between groups. The probability to reproduce sexually in the year after the manipulation, and the biomass allocated to this reproduction, were not affected by the experimental treatment.     

An experimental demonstration of the cost of sex and a potential resource limitation on reproduction in the moss Pterygoneurum (Pottiaceae)

The cost of sexual reproduction is incurred when the current reproductive episode contributes to a a decline in future plant performance. To test the hypotheses that a trade-off exists between current sexual reproduction and subsequent clonal regeneration and that resources limit reproduction and regeneration, plants of the widespread moss Pterygoneurum ovatum were subjected to induced sporophytic abortion, upper leaf removal, and nutrient amendment treatments. Sexually reproducing plants were slower or less likely to produce regenerative structures (protonemata or shoots) and produced fewer regenerative tissue areas or structures. The ability and the timeline to reproduce sexually and regenerate clonally were unaffected by an inorganic nutrient amendment. However, when leaves subtending the sporophyte were removed, the sporophytes were less likely to mature, tended to take a longer time to mature, and were smaller compared to sporophytes from shoots with a full complement of upper leaves. Our findings indicate that plants investing in sexual reproduction suffer a cost of decreased clonal regeneration and indicate that sporophyte maturation is resource-limited, with upper leaves contributing to the nutrition of the sporophyte. This study represents only the second explicit experimental demonstration of a trade-off between sexual and asexual reproduction in bryophytes.     

Large-scale analysis of 73 329 physcomitrella plants transformed with different gene disruption libraries: production parameters and mutant phenotypes

Gene targeting in the moss Physcomitrella patens has created a new platform for plant functional genomics. We produced a mutant collection of 73 329 Physcomitrella plants and evaluated the phenotype of each transformant in comparison to wild type Physcomitrella. Production parameters and morphological changes in 16 categories, such as plant structure, colour, coverage with gametophores, cell shape, etc., were listed and all data were compiled in a database (mossDB). Our mutant collection consists of at least 1804 auxotrophic mutants which showed growth defects on minimal Knop medium but were rescued on supplemented medium. 8129 haploid and 11 068 polyploid transformants had morphological alterations. 9 % of the haploid transformants had deviations in the leaf shape, 7 % developed less gametophores or had a different leaf cell shape. Other morphological deviations in plant structure, colour, and uniformity of leaves on a moss colony were less frequently observed. Preculture conditions of the plant material and the cDNA library (representing genes from either protonema, gametophore or sporophyte tissue) used to transform Physcomitrella had an effect on the number of transformants per transformation. We found correlations between ploidy level and plant morphology and growth rate on Knop medium. In haploid transformants correlations between the percentage of plants with specific phenotypes and the cDNA library used for transformation were detected. The number of different cDNAs present during transformation had no effect on the number of transformants per transformation, but it had an effect on the overall percentage of plants with phenotypic deviations. We conclude that by linking incoming molecular, proteome, and metabolome data of the transformants in the future, the database mossDB will be a valuable biological resource for systems biology.     

Sexual conflict and the alternation of haploid and diploid generations

Land plants possess a multicellular diploid stage (sporophyte) that begins development while attached to a multicellular haploid progenitor (gametophyte). Although the closest algal relatives of land plants lack a multicellular sporophyte, they do produce a zygote that grows while attached to the maternal gametophyte. The diploid offspring shares one haploid set of genes with the haploid mother that supplies it with resources and a paternal haploid complement that is not shared with the mother. Sexual conflict can arise within the diploid offspring because the offspring's maternal genome will be transmitted in its entirety to all other sexual and asexual offspring that the mother may produce, but the offspring's paternally derived genes may be absent from these other offspring. Thus, the selective forces favouring the evolution of genomic imprinting may have been present from the origin of modern land plants. In bryophytes, where gametophytes are long-lived and capable of multiple bouts of asexual and sexual reproduction, we predict strong sexual conflict over allocation to sporophytes. Female gametophytes of pteridophytes produce a single sporophyte and often lack means of asexual reproduction. Therefore, sexual conflict is predicted to be attenuated. Finally, we explore similarities among models of mate choice, offspring choice and segregation distortion.     

Restriction of sexual reproduction in the moss Racomitrium lanuginosum along an elevational gradient

1. Terrestrial plant populations located at the margins of species’ distributions often display reduced sexual reproduction and an increased reliance on asexual reproduction. One hypothesis to explain this phenomenon is that the decline is associated with environmental effects on the energetic costs to produce reproductive organs.
2. In order to clarify the changing processes of sexual reproduction along an elevational gradient, we investigated the sexual reproductive parameters, such as the number of sporophytes and gametangia, in Racomitrium lanuginosum, a dioicous moss found on Mt. Fuji.
3. Matured sporophytes were present only below 3,000 m, and the number of sporophytes per shoot tended to be lower at higher elevation habitats. The numbers of male inflorescences per shoot and antheridia per inflorescence and shoot significantly decreased with increasing elevation. In contrast, the numbers of female inflorescences per shoot and archegonia per inflorescence and shoot varied little across elevations.
4. Synthesis. Our results suggest that the reasons for this limitation are assumed to be limitations in sporophyte development that result in abortion, and the spatial segregation between males and females. Possible reasons for the abortion of sporophytes are the inhibitory effects of low air temperature, a shortened growth period, and winter environmental conditions at higher elevations. Remarkable differences between male and female on various reproductive parameters found in this study are thought to affect the mode of sexual reproduction under the harsh environment. These differences between males and females may be caused by differences in the costs of production and development of gametangia, sensitivity to environmental stressors, and phenological patterns.

     

Cryptochrome light signals control development to suppress auxin sensitivity in the moss Physcomitrella patens

The blue light receptors termed cryptochromes mediate photomorphological responses in seed plants. However, the mechanisms by which cryptochrome signals regulate plant development remain obscure. In this study, cryptochrome functions were analyzed using the moss Physcomitrella patens. This moss has recently become known as the only plant species in which gene replacement occurs at a high frequency by homologous recombination. Two cryptochrome genes were identified in Physcomitrella, and single and double disruptants of these genes were generated. Using these disruptants, it was revealed that cryptochrome signals regulate many steps in moss development, including induction of side branching on protonema and gametophore induction and development. In addition, the disruption of cryptochromes altered auxin responses, including the expression of auxin-inducible genes. Cryptochrome disruptants were more sensitive to external auxin than wild type in a blue light-specific manner, suggesting that cryptochrome light signals repress auxin signals to control plant development.     

树干附生尖叶拟船叶藓的孢子体分布格局和败育研究

通过野外定位考察和实验室观察分析,结果显示:(1)贵州梵净山树干附生尖叶拟船叶藓的孢子体种群80%分布在树干的基部;(2)尖叶拟船叶藓的孢子体在其主茎和一到四次分枝上皆有分布,但在一次分枝上分布最多,并且一次分枝上的与主茎或其它各次分枝上分布的之间存在显著差异;(3)孢子体败育发生在胚胎发育时期、孢蒴膨大期或者孢子形成期等3个时期,孢子体败育率为7.3%,败育孢子体的平均生物量为正常成熟的43.3%.表明尖叶拟船叶藓孢子体种群偏少且孢子体败育率低是其重要的生物学特征.     

Effects of Light, pH, Temperature, and Crowding on Megaspore Germination and Sporophyte Formation in Marsilea

Megaspore germination and sporophyte formation of Marsilea vestitaH. and G. was studied under different light, pH, temperature,and crowding conditions during a 6 d experimental period. Maximumgermination and sporophyte development occurs under relativelylow light intensity. Darkness and high light intensity inhibitsporophyte development. Selected wavelengths of light (red,far-red, green, blue) and darkness reduce both megaspore germinationand sporophyte development as compared to white light. Megasporesand sporophytes show maximum development at 25 ?C in light,whereas their development is reduced at all temperatures indarkness. The optimum pH range for megaspore germination ispH 7–8 and that for sporophyte development is pH 7. Sporocarpcontents alter the pH of unbuffered acidic and basic media towarda more optimal growth condition (pH 6–8) for megasporegermination. Megaspore germination and sporophyte developmentvary inversely with conditions of crowding. Root and leaf growthon developed sporophytes is very similar in most treatments.     

The cost of realized sexual reproduction: assessing patterns of reproductive allocation and sporophyte abortion in a desert moss

The desert moss Syntrichia caninervis exhibits one of the most skewed sex ratios in the plant kingdom, with female individuals far outnumbering male individuals (exceeding 14♀:1♂). The "cost of sex hypothesis" derives from allocational theory and predicts that the sex which is most expensive should be the rarer sex. This hypothesis, which, as considered here represents the realized cost of sexual reproduction, is contingent upon two assumptions that are explored: (1) that male sex expression is more expensive than female sex expression, and (2) that sexual reproduction is resource limited. Using inflorescence biomass and discounting sperm, male sex expression was found to be in the neighborhood of one order of magnitude more expensive than female sex expression, and this difference is reflected in higher numbers of gametangia per male inflorescence, presence of paraphyses in male inflorescences, and a much longer developmental time for male inflorescences. The realized cost of female reproduction from two communities dominated by S. caninervis was found to be lower than the realized cost of male sexual reproduction. Resource-limited reproduction was assessed by determining the frequency of sporophyte abortion, the age distribution of sporophyte abortions, and patterns of sporophyte abortion that may be density dependent. Among ten sexually reproducing populations, abortive sporophytes occurred at a frequency of 0.64. Abortive sporophytes averaged 8% the mass of mature sporophytes, and cohort sporophytes from the same individual female were found to abort in a density-dependent pattern. We conclude that the two assumptions, upon which the cost of sex hypothesis depends, are supported.     

Two ANGUSTIFOLIA genes regulate gametophore and sporophyte development in Physcomitrella patens

In Arabidopsis thaliana the ANGUSTIFOLIA (AN) gene regulates the width of leaves by controlling the diffuse growth of leaf cells in the medio‐lateral direction. In the genome of the moss Physcomitrella patens, we found two normal ANs (PpAN1‐1 and 1‐2). Both PpAN1 genes complemented the A. thaliana an‐1 mutant phenotypes. An analysis of spatiotemporal promoter activity of each PpAN1 gene, using transgenic lines that contained each PpAN1‐promoter– uidA (GUS) gene, showed that both promoters are mainly active in the stems of haploid gametophores and in the middle to basal region of the young sporophyte that develops into the seta and foot. Analyses of the knockout lines for PpAN1‐1 and PpAN1‐2 genes suggested that these genes have partially redundant functions and regulate gametophore height by controlling diffuse cell growth in gametophore stems. In addition, the seta and foot were shorter and thicker in diploid sporophytes, suggesting that cell elongation was reduced in the longitudinal direction, whereas no defects were detected in tip‐growing protonemata. These results indicate that both PpAN1 genes in P. patens function in diffuse growth of the haploid and diploid generations but not in tip growth. To visualize microtubule distribution in gametophore cells of P. patens, transformed lines expressing P. patens α‐tubulin fused to sGFP were generated. Contrary to expectations, the orientation of microtubules in the tips of gametophores in the PpAN1‐1/1‐2 double‐knockout lines was unchanged. The relationships among diffuse cell growth, cortical microtubules and AN proteins are discussed.     

The time of fruiting of Ulota Bruchii Hornsch. and U. crispa Brid.

Abstract

For obscure reasons, sporophytes of the dioicous Hamatocaulis vernicosus are currently unknown in France. With the aim of understanding this failure of sporophyte production we investigated (1) sexual phenology, (2) sex ratio pattern at different spatial scales, (3) limitation of sporophyte formation by the availability of only one sex, (4) limitation of sporophyte formation caused by the distance between male and female, (5) location of sporophytes and (6) the consevation implications of this failure of sporophyte production. Principal results show that phenology cannot explain the failure of sporophyte production. At the regional scale, sporophyte formation is prevented by the fact that several mountain ranges have single-sex populations. The production of spore capsules relies on a strict combination of factors at the local scale: occurrence of sexually expressed mixed-sex colonies, a short distance between male and female individuals and favourable environmental factors (light grazing, high water table). In the Massif Central of France spore production is unlikely because of current unfavourable conditions. Fertility patterns appeared useful in a conservation context.     

DEVELOPMENT AND GAMETOPHORE INITIATION IN THE MOSS PYLAISIELLA SELWYNII AS INFLUENCED BY AGROBACTERIUM TUMEFACIENS

Spores of the heterotrichous moss Pylaisiella selwynii Kindb. were sown in a defined inorganic liquid culture medium and incubated at 27 C with a 16-hr photoperiod. They germinated at 7–10 days, and formed a few caulonemal buds at 27–30 days which developed into gametophores by 40 days. Bud formation and gametophore development followed a pattern common to many mosses. Addition of a virulent strain of Agrobacterium tumefaciens (B6) to the moss cultures increased bud formation and hastened the time of their appearance by 5–6 days. With 10⁹ or more bacteria per ml of moss culture medium the percentage of plants with gametophores at day 35 after the spores were sown was 96 % or greater, as opposed to 0–24 % in the controls. The mean number of gametophores per responding plant was also increased from one per plant in controls to 4–6 per plant in inoculated cultures. Addition of the bacterium at day 17–18 of culture was as effective as early additions of the bacterium, suggesting that the moss must become ready to bud before the bacterium can influence its development. The promotion of gametophore formation was directly related to the number of bacteria added and depended upon the presence of viable bacteria. The supernatant from bacterial cultures did not promote gametophore formation. The changes induced by A. tumefaciens were similar to those reported for cytokinins.     

The cuticle on the gametophyte calyptra matures before the sporophyte cuticle in the moss Funaria hygrometrica (Funariaceae)

? Premise of the study: In vascular plants, leaf primordia prevent desiccation of the shoot apical meristem. Lacking leaves, the undifferentiated moss sporophyte apex is covered by the calyptra, a cap of maternal gametophyte tissue that is hypothesized to function in desiccation protection. Herein, we compare cuticle development on the calyptra and sporophyte to assess the calyptra's potential to protect the sporophyte from desiccation. As the first comprehensive study of moss sporophyte cuticle development, this research broadens our perspectives on cuticle development and evolution across embryophytes. ? Methods: Calyptrae and sporophytes at nine developmental stages were collected from a laboratory-grown population of the moss Funaria hygrometrica. Tissues were embedded, sectioned, then examined using transmission electron microscopy. Epidermal cells were measured for thickness of the cuticle layers, cell wall thickness, and lumen size. ? Key results: The calyptra cuticle develops precociously and reaches maturity before the sporophyte cuticle. Calyptrae are covered by a four-layered cuticle at all stages, whereas sporophyte cuticle maturation is delayed until sporangium formation. The development and thickening of the sporophyte cuticle occurs in an acropetal wave. ? Conclusions: A multilayered calyptra cuticle at the earliest developmental stages is consistent with its ability to protect the immature sporophyte from desiccation. Young sporophytes lack a complex cuticle and thus may require protection, whereas in older sporophytes a mature cuticle develops. The moss calyptra is not a vestigial structure, but rather the calyptra's role in preventing desiccation offers a functional explanation for calyptra retention during the 450 Myr of moss evolution.     

Photoperiodic long-day control of sporophyll and hair formation in the brown alga Undaria pinnatifida

Two photoperiodic responses, the development of sporophylls and hairs, havebeen quantified in sporophytes of the brown alga Undaria pinnatifida. In a finalexperiment, the algae were cultivated in outdoor, 2000-L seawater tanks in agreenhouse for up to 12 weeks, and daylength was regulated by automatic blindsmounted on top of the tanks. Vegetative young sporophytes were treated undershort-day (SD; 8 h light per day) or long-day conditions (LD; 16 h light perday), at 12 h light per day or in a night-break regime (NB; 8 h light per day,7.5 h dark, 1 h light, 7.5 h dark). The earliest sporophyll development wasobserved 6, 7 or 9 weeks under LD, NB or SD conditions, respectively. After 12 weeksthe sporophylls were significantly longer and wider under LD or NB conditions than inthe SD regime, and only half of the experimental algae had formed sporophyllsunder SD conditions, but all algae under LD or NB conditions. In a foregoing 7-weekculture experiment performed in 300-lL indoor tanks, enhanced sporophyll formationhad also been observed under LD and not under SD conditions (NB omitted). In bothexperiments, blade elongation rates remained high until the end of theexperiments in SD, but declined during sporophyll initiation in LD, NB or at 12 hlight per day. Another difference caused by photoperiod was observed in regard to thedevelopment of surface hair spots which occurred in both experiments on the bladesin LD, NB or at 12 h light per day with identical densities, but were completelylacking under SD conditions. It is concluded that U. pinnatifida is afacultatative long-day plant in regard to reproduction forming vigorously sporophyllsin long days, and an obligate long-day plant in regard to hair formation.     

Structure and Function of Transfer Cells in the Sporophyte Haustorium of Funaria hygrometrica Hedw: III. TRANSLOCATION OF ASSIMILATE INTO THE ATTACHED SPOROPHYTE AND ALONG THE SETA OF ATTACHED AND EXCISED SPOROPHYTES

Translocation of products of photosynthesis from gametophyteto sporophyte was examined in the moss Funaria hygrometricaHedw., as an adjunct to companion studies on the ultrastructureof the sporophyte haustorium and its capacity for absorptionof sugars in vitro. Labelled products derived from gametophyticphotosynthesis are transported to the sporophyte at an approximatelylinear rate for up to 12 h after a pulse treatment with ¹⁴CO₂.Large sporophytes receive label at a greater rate than smallerones. Transport is inhibited under conditions of water stress,and by lack of light, though darkening the sporophyte alonehas no effect. Movement of label from the haustorium along theseta occurs at a velocity of 1–3 mm h^–1, and issimilar to the onward movement of label derived from [³H]glucosesupplied to the haustorium in vitro.