Interploidy gene flow via a 'pentaploid bridge' and ploidy reduction in Cystopteris fragilis fern complex (Cystopteridaceae: Polypodiales)

KEY MESSAGE

Our results indicate the existence of interploidy gene flow in Cystopteris fragilis, resulting in sexual triploid and diploid gametophytes from pentaploid parents. Similar evolutionary dynamics might operate in other fern complexes and need further investigation. Polyploidization and hybridization are a key evolutionary processes in ferns. Here, we outline an interploidy gene flow pathway operating in the polyploid Cystopteris fragilis complex. The conditions necessary for the existence of this pathway were tested. A total of 365 C. fragilis individuals were collected covering representatives of all three predominant ploidy levels (tetraploid, pentaploid, and hexaploid), cultivated, had their ploidy level estimated by flow cytometry, and their spores collected. The spores, as well as gametophytes and sporophytes established from them, were analysed by flow cytometry. Spore abortion rate was also estimated. In tetraploids, we observed the formation of unreduced (tetraploid) spores (ca 2%). Collected pentaploid individuals indicate ongoing hybridization between ploidy levels. Pentaploids formed up to 52% viable spores, ca 79% of them reduced, i.e. diploid and triploid. Reduced spores formed viable gametophytes, and, in the case of triploids, filial hexaploid sporophytes, showing evidence of sexual reproduction. Some tetraploid sporophytes reproduce apomictically (based on uniform ploidy of their metagenesis up to filial sporophytes). Triploid and diploid gametophytes from pentaploid parents are able to mate among themselves, or with "normal" reduced gametophytes from the sexual tetraploid sporophytes (the dominant ploidy level in the sporophytes in this populations), to produce tetraploid, pentaploid, and hexaploid sporophytes, allowing for geneflow from the pentaploids to both the tetraploid and hexaploid populations. Similar evolutionary dynamics might operate in other fern complexes and need further investigation.

Effects of antifouling compounds on the growth of macroalgae Undaria pinnatifida

Seaweeds are some of the principal primary producers of marine environments, and they are important ecological elements of coastal ecosystems. The effects of harmful chemicals on seaweeds may adversely affect coastal ecosystems, hence we aimed to develop a new phytotoxicity test using the gametophytes of a common temperate kelp species, Undaria pinnatifida (KU-1630), for the widely used antifouling chemical substances Cybutryne, Diuron, Cu2+, and Zn2+. Toxicity to gametophytes of U. pinnatifida was assessed by comparing the relative growth rate (RGR) at the logarithmic growth phase. Fragmentation method, initial algal biomass, photon irradiance, and adhesive period were investigated for developing optimal test conditions. Cybutryne exposure tests were performed with seven replicates and control, the RGR ranging from 0.17 to 0.19, while mean 7-day EC50 and no observed effect concentration (NOEC) were 5.1 μg/L and 1.8 μg/L, respectively. The 7-day EC50 for other antifoulants was 14 μg/L for Diuron, 17 μg/L for Cu2+, and 1500 μg/L for Zn2+. This test method demonstrated high sensitivity and reproducibility, and it may be added to the routine methods used for toxicity evaluation of hazardous chemicals.

In vitro spore germination and phytoremediation of Hg and Pb using gametophytes of Pityrogramma calomelanos

Few pteridophytes have proven the capacity to accumulate and remediate heavy metals from contaminated soils. Pityrogramma calomelanos, a non-seasonal fast-growing, a cosmopolitan fern, is a good indicator of environmental conditions, was used in the present study. The life cycle of ferns alternates with haploid gametophyte and diploid sporophyte. The present study was undertaken to access the effect of mercury, in form of mercury (II) chloride [(HgCl₂)] and lead as lead nitrate [Pb(NO₃)₂] in developmental studies using in vitro spore germination. Periodic recording of the germination, protonemal growth, rhizoid formation and differentiation of sex organs in different concentrations of heavy metals were conducted for a period of 6 weeks. It was found that the percentage of spore germination and the number of protonemal cells reduced significantly causing developmental defects in the presence of HgCl₂ as compared to Pb(NO₃)₂ (p < 0.0001). A significant decrease in the number of archegonial count and chlorophyll content was observed in different concentrations of the heavy metals tested. Gametophytes of P. calomelanos recorded lead uptake of 646.51 ± 0.93 mg/kg in treatments of 25 ppm of lead and high mercury accumulation up to 1,885 ± 1.98 mg/kg at 10 ppm of mercury, indicating successful uptake of heavy metals. Novelty statement: Pityrogramma calomelanos is gaining interest amongst pteridologists upon proving its exclusive capacity of phytoremediation. It is superior in comparison to the most popular, patented fern Pteris vittata. Our study demonstrates the effective use of the promising fern in its simplest, nonvascular form of gametophytes as a phytoremediation agent in controlled conditions.

Rapid toxicity assessment of six antifouling booster biocides using a microplate-based chlorophyll fluorescence in Undaria pinnatifida gametophytes

Biocides of antifouling agents can cause problems in marine ecosystems by damaging to non-target algal species. Aquatic bioassays are important means of assessing the quality of water containing mixtures of contaminants and of providing a safety standard for water management in an ecological context. In this study, a rapid, sensitive and inexpensive test method was developed using free-living male and female gametophytes of the brown macroalga Undaria pinnatifida. A conventional fluorometer was employed to evaluate the acute (48 h) toxic effects of six antifouling biocides: 4,5-Dichloro-2-octyl-isothiazolone (DCOIT), diuron, irgarol, medetomidine, tolylfluanid, zinc pyrithione (ZnPT). The decreasing toxicity in male and female gametophytes as estimated by EC50 (effective concentration at which 50% inhibition occurs) values was: diuron (0.037 and 0.128 mg l-1, respectively) > irgarol (0.096 and 0.172 mg l-1, respectively) > tolylfluanid (0.238 and 1.028 mg l-1, respectively) > DCOIT (1.015 and 0.890 mg l-1, respectively) > medetomidine (12.032 and 12.763 mg l-1, respectively). For ZnPT, 50% fluorescence inhibition of U. pinnatifida gametophytes occurred at concentrations above 0.4 mg l-1. The Undaria method is rapid, simple, practical, and cost-effective for the detection of photosynthesis-inhibiting biocides, thus making a useful tool for testing the toxicity of antifouling agents in marine environments.

Studies on the gametophytic development, mating behaviour and reproductive biology of Macrothelypteris torresiana (Gaudich.) Ching (Thelypteridaceae)

Macrothelypteris torresiana is a terrestrial fern belongs to the family Thelypteridaceae. It is very imperative to know the germination and growth pattern of this fern to make strategy for ex- situ conservation. In the present study germination of spore, developmental pattern of prothallium with particular emphasis on emergence of antheridia as well as archegonia, their fertilization and development of sporophytes were studied. The spores were spheroidal or reniform with broadly winged fimbriate perispore having average size of 48 ± 3.6 × 39 ± 4.2 μm. The spores started germinating just after 6 days of plating and percentage of germination was 94%. The germination pattern of spore was Vittaria type and development of gametophyte was Aspidium type. After 27 days of plating, a very distinct cordate-shaped adult gametophyte with deep apical notch and unicellular papillate hairs throughout the gametophyte was developed. The rhizoids appeared away from the apical notch of the gametophyte. The gametophyte first developed archegonia on 32^nd day, whereas antheridia were developed on 42^nd day. In isolate culture the gametophytes did not develop any sporophyte whereas in composite culture juvenile sporophytes were emerged on 77^th day. This suggests the plant has ability to reproduce only through inter-gametophytic selfing and crossing, hence decreasing the plant's capacity for colonization in a particular locality.

Increased temperature but not pCO2 levels affect early developmental and reproductive traits of the economically important habitat-forming kelp Lessonia trabeculata

The effects of ocean warming and ocean acidification on developmental and reproductive traits of Lessonia trabeculata were evaluated. Meiospores were cultured for 35 days in an experimental mesocosm where temperature (~15 and 19 °C) and partial CO2 pressure (pCO2, ~400 and 1300 μatm) were controlled. The results indicate that germination was reduced at 19 °C, whereas the increase of pCO2 only had effects at 15 °C. Likewise, the increase in temperature significantly affected the vegetative growth of female gametophytes. Sex ratio was not affected significantly by any of the variables studied. Fertility and reproductive success decreased by about 50% at 19 °C. The pCO2 levels had no significant effects on most early developmental traits. The results suggest that ocean warming or periodic warming events (e.g. an El Niño event) might affect the recruiting capacity of this or other similar species by affecting their early developmental stages.

Arabinogalactan proteins and their sugar chains: functions in plant reproduction, research methods, and biosynthesis

The arabinogalactan protein (AGP) family is one of the most complex protein families and is ubiquitous in the plant kingdom. Moreover, it has been demonstrated to play various roles during plant reproduction. A typical AGP contains a hydroxyproline-rich core protein with high heterogeneity and varying numbers of polysaccharide side chains. However, the functions of the polysaccharide components (i.e. AG sugar chains) remain largely unknown due to the general difficulties associated with studying sugar chains in glycobiology. In recent years, methodological breakthroughs have resulted in substantial progress in AGP research. Here, we summarise the multiple roles of AGPs during plant gametophyte development and male-female communication, with a focus on recent advances. In addition, we discuss the analytical tools used in AGP research, and the biosynthesis and function of AG sugar chains. A comprehensive understanding of the AGP family will help clarify the mechanisms precisely controlling reproductive processes.

Regeneration of drought-stressed gametophytes of the epiphytic fern, Pyrrosia pilosellodes (L.) Price

The epiphytic habitat represents a highly dynamic environment, and water deficit is one of the common factors that affects growth and development of epiphytes. Gametophytes of the epiphytic fern, Pyrrosia piloselloides (L.) Price, were able to tolerate up to 50 days of drought. Upon rehydration, cells that recovered from water stress were capable of forming new gametophytes. The ability of gametophytes to recover from desiccation plays an important role in the survival and growth of the fern species under natural conditions.