Analysis of auxin responses in the fern Ceratopteris richardii identifies the developmental phase as a major determinant for response properties.

The auxin signaling molecule regulates a range of plant growth and developmental processes. The core transcriptional machinery responsible for auxin-mediated responses is conserved across all land plants. Genetic, physiological and molecular exploration in bryophyte and angiosperm model species have shown both qualitative and quantitative differences in auxin responses. Given the highly divergent ontogeny of the dominant gametophyte (bryophytes) and sporophyte (angiosperms) generations, however, it is unclear whether such differences derive from distinct phylogeny or ontogeny. Here, we address this question by comparing a range of physiological, developmental and molecular responses to auxin in both generations of the model fern Ceratopteris richardii. We find that auxin response in Ceratopteris gametophytes closely resembles that of a thalloid bryophyte, whereas the sporophyte mimics auxin response in flowering plants. This resemblance manifests both at the phenotypic and transcriptional levels. Furthermore, we show that disrupting auxin transport can lead to ectopic sporophyte induction on the gametophyte, suggesting a role for auxin in the alternation of generations. Our study thus identifies developmental phase, rather than phylogeny, as a major determinant of auxin response properties in land plants.

The size diversity of the Pteridaceae family chloroplast genome is caused by overlong intergenic spacers.

BACKGROUND: While the size of chloroplast genomes (cpDNAs) is often influenced by the expansion and contraction of inverted repeat regions and the enrichment of repeats, it is the intergenic spacers (IGSs) that appear to play a pivotal role in determining the size of Pteridaceae cpDNAs. This provides an opportunity to delve into the evolution of chloroplast genomic structures of the Pteridaceae family. This study added five Pteridaceae species, comparing them with 36 published counterparts. RESULTS: Poor alignment in the non-coding regions of the Pteridaceae family was observed, and this was attributed to the widespread presence of overlong IGSs in Pteridaceae cpDNAs. These overlong IGSs were identified as a major factor influencing variations in cpDNA size. In comparison to non-expanded IGSs, overlong IGSs exhibited significantly higher GC content and were rich in repetitive sequences. Species divergence time estimations suggest that these overlong IGSs may have already existed during the early radiation of the Pteridaceae family. CONCLUSIONS: This study reveals new insights into the genetic variation, evolutionary history, and dynamic changes in the cpDNA structure of the Pteridaceae family, providing a fundamental resource for further exploring its evolutionary research.

Control of leaf development in the water fern Ceratopteris richardii by the auxin efflux transporter CrPINMa in the CRISPR/Cas9 analysis.

BACKGROUND: PIN-FORMED genes (PINs) are crucial in plant development as they determine the directionality of auxin flow. They are present in almost all land plants and even in green algae. However, their role in fern development has not yet been determined. This study aims to investigate the function of CrPINMa in the quasi-model water fern Ceratopteris richardii. RESULTS: CrPINMa possessed a long central hydrophilic loop and characteristic motifs within it, which indicated that it belonged to the canonical rather than the non-canonical PINs. CrPINMa was positioned in the lineage leading to Arabidopsis PIN6 but not that to its PIN1, and it had undergone numerous gene duplications. CRISPR/Cas9 genome editing had been performed in ferns for the first time, producing diverse mutations including local frameshifts for CrPINMa. Plants possessing disrupted CrPINMa exhibited retarded leaf emergence and reduced leaf size though they could survive and reproduce at the same time. CrPINMa transcripts were distributed in the shoot apical meristem, leaf primordia and their vasculature. Finally, CrPINMa proteins were localized to the plasma membrane rather than other cell parts. CONCLUSIONS: CRISPR/Cas9 genome editing is feasible in ferns, and that PINs can play a role in fern leaf development.

Areas of endemism of Pteridaceae (Polypodiopsida) in Brazil: a first approach.

Areas of endemism (AoE) comprise regions host to two or more endemic taxa, whose distributional limits are congruent and not random. These areas are important for two reasons: they comprise the smallest geographic units for biogeographic analyses and they are priority targets for conservation actions. Ferns are a monophyletic group that despite having a wide geographic distribution, concentrates great species richness and endemism in some regions (centres). The southern and southeastern regions of Brazil comprise one of these centres for the Neotropics. This study aims to verify the AoE of Pteridaceae in Brazil and examine whether the results obtained here are congruent with areas already delimited for other groups and whether there is spatial correspondence between the AoE and Conservation Units. To this end, a database was created with collection records of the 205 Pteridaceae species occurring in Brazil based on a review of herbaria. We analysed 23 815 records for 205 Pteridaceae species using Endemicity Analysis (NDM-VNDM), selecting the fill and assumed parameters, and 1°, 2° and 3° grid-cells. The consensus of 158 AoE, using different grid sizes, was calculated, and subsequently, generalized AoE were established. The Guiana Shield, southern Brazil, southeastern Brazil, and southeastern Bahia were considered generalized AoE. These areas correspond to those found for animals and angiosperms, and in previous studies with ferns. Furthermore, two areas, Acre and Mato Grosso do Sul, were recovered only on grids with 2° and 3°. It will be essential to conduct more research to confirm the persistence of both AoE (Acre and Mato Grosso do Sul), especially after expanding sampling. Most endemic species distribution points occur outside protected areas, demonstrating an alarming situation regarding the conservation of these taxa. In addition, fern distribution data could (and should) be used in conservation practices, programmes and policies, given that they are good ecological indicators and that the distribution of ferns may not reflect that of angiosperms and animals.

Polyploid goldback and silverback ferns (Pentagramma) occupy a wider, colder, and wetter bioclimatic niche than diploid counterparts.

PREMISE: The western North American fern genus Pentagramma (Pteridaceae) is characterized by complex patterns of ploidy variation, an understanding of which is critical to comprehending both the evolutionary processes within the genus and its current diversity. METHODS: We undertook a cytogeographic study across the range of the genus, using a combination of chromosome counts and flow cytometry to infer ploidy level. Bioclimatic variables and elevation were used to compare niches. RESULTS: We found that diploids and tetraploids are common and widespread, and triploids are rare and sporadic; in contrast with genome size inferences in earlier studies, no hexaploids were found. Diploids and tetraploids show different geographic ranges: only tetraploids were found in the northernmost portion of the range (Washington, Oregon, and British Columbia) and only diploids were found in the Sierra Nevada of California. Diploid, triploid, and tetraploid cytotypes were found to co-occur in relatively few localities: in the southern (San Diego County, California) and desert Southwest (Arizona) parts of the range, and along the Pacific Coast of California. CONCLUSIONS: Tetraploids occupy a wider bioclimatic niche than diploids both within P. triangularis and at the genus-wide scale. It is unknown whether the wider niche of tetraploids is due to their expansion upon the diploid niche, if diploids have contracted their niche due to competition or changing abiotic conditions, or if this wider niche occupancy is due to multiple origins of tetraploids.

Adaptive evolution and co-evolution of chloroplast genomes in Pteridaceae species occupying different habitats: overlapping residues are always highly mutated.

BACKGROUND: The evolution of protein residues depends on the mutation rates of their encoding nucleotides, but it may also be affected by co-evolution with other residues. Chloroplasts function as environmental sensors, transforming fluctuating environmental signals into different physiological responses. We reasoned that habitat diversity may affect their rate and mode of evolution, which might be evidenced in the chloroplast genome. The Pteridaceae family of ferns occupy an unusually broad range of ecological niches, which provides an ideal system for analysis. RESULTS: We conducted adaptive evolution and intra-molecular co-evolution analyses of Pteridaceae chloroplast DNAs (cpDNAs). The results indicate that the residues undergoing adaptive evolution and co-evolution were mostly independent, with only a few residues being simultaneously involved in both processes, and these overlapping residues tend to exhibit high mutations. Additionally, our data showed that Pteridaceae chloroplast genes are under purifying selection. Regardless of whether we grouped species by lineage (which corresponded with ecological niches), we determined that positively selected residues mainly target photosynthetic genes. CONCLUSIONS: Our work provides evidence for the adaptive evolution of Pteridaceae cpDNAs, especially photosynthetic genes, to different habitats and sheds light on the adaptive evolution and co-evolution of proteins.

Insights into the evolutionary history and taxonomic status of Sinopteris (Pteridaceae).

As an endemic Chinese genus, Sinopteris C. Chr. & Ching was once considered an early diverged taxon of cheilanthoid ferns, and its taxonomic status has long been controversial. In this study, eight datasets spanning the complete chloroplast genomes and three nuclear genes were used to reconstruct the phylogeny of Sinopteris and its relatives. In addition, combining morphological analyses, divergence time estimation, and ancestral trait reconstruction, the origin and evolutionary history of Sinopteris were comprehensively discussed. Based on the complete chloroplast genome dataset, our analyses yielded a phylogram with all clades strongly supported (ML-BS = 100, BI-PP = 1.0), and the topology was almost identical to that based on the concatenated sequences of nrDNA, CRY2, and IBR3. Two species of Sinopteris were united and sister to Aleuritopteris niphobola (C. Chr.) Ching. They constituted a stable monophyletic group embedded in Aleuritopteris Fée. This was also consistent with the results of morphological analyses. Divergence time estimation indicated that the clade of Aleuritopteris and Sinopteris originated in the early Miocene (ca. 16.80 Ma) and experienced two rapid diversifications, which could coincide with environmental heterogeneity caused by the progressive uplift of the Himalayas and the intense uplift of the Hengduan Mountains. Sinopteris originated in the late Miocene (ca. 6.96 Ma), accompanied by the sharp intensifications of Asian Monsoon, and began to diversify at 2.34 Ma, following the intense uplift of the Hengduan Mountains. Ancestral character reconstruction showed that monangial sori and subsessile sporangia were clearly late derived states rather than early diverged states. Both the molecular phylogenetic and morphological analyses support the inclusion of Sinopteris in Aleuritopteris.

Systematics and biogeography of the Old World fern genus Antrophyum.

Antrophyum is one of the largest genera of vittarioid ferns (Pteridaceae) and is most diverse in tropical Asia and the Pacific Islands, but also occurs in temperate Asia, Australia, tropical Africa and the Malagasy region. The only monographic study of Antrophyum was published more than a century ago and a modern assessment of its diversity is lacking. Here, we reconstructed a comprehensively sampled and robustly supported phylogeny for the genus based on four chloroplast markers using Bayesian inference, maximum likelihood and maximum parsimony analyses. We then explored the evolution of the genus from the perspectives of morphology, systematics and historical biogeography. We investigated nine critical morphological characters using a morphometric approach and reconstructed their evolution on the phylogeny. We describe four new species and provide new insight into species delimitation. We currently recognize 34 species for the genus and provide a key to identify them. The results of biogeographical analysis suggest that the distribution of extant species is largely shaped by both ancient and recent dispersal events.

Once more unto the breach, dear friends: Resolving the origins and relationships of the Pellaea wrightiana hybrid complex.

PREMISE: The taxonomic status of Wright's cliff brake fern, Pellaea wrightiana, has been in dispute ever since it was first described by Hooker in 1858. Previously published evidence suggested that this "taxon" may represent a polyploid complex rather than a single discrete species, a hypothesis tested here using a multifaceted analytical approach. METHODS: Data derived from cytogenetics, spore analyses, leaf morphometrics, enzyme electrophoresis, and phylogenetic analyses of plastid and nuclear DNA sequences are used to elucidate the origin, relationships, and taxonomic circumscription of P. wrightiana. RESULTS: Plants traditionally assigned to this taxon represent three distinct polyploids. The most widespread, P. wrightiana, is a fertile allotetraploid that arose through hybridization between two divergent diploid species, P. truncata and P. ternifolia. Sterile triploids commonly identified as P. wrightiana, were found to be backcross hybrids between this fertile tetraploid and diploid P. truncata. Relatively common across Arizona and New Mexico, they are here assigned to P. ×wagneri hyb. nov. In addition, occasional sterile tetraploid plants assigned to P. wrightiana are shown here to be hybrids between the fertile allotetraploid and the tetraploid P. ternifolia subsp. arizonica. These tetraploid hybrids originated independently in two regions of parental sympatry (southern Arizona and west Texas) and are here assigned to P. ×gooddingii hyb. nov. CONCLUSIONS: Weaving together data from a diversity of taxonomic approaches, we show that plants identified as P. wrightiana represent three morphologically distinguishable polyploids that have arisen through repeated hybridization events involving the divergent sexual taxa P. ternifolia and P. truncata.

A Large Intergenic Spacer Leads to the Increase in Genome Size and Sequential Gene Movement around IR/SC Boundaries in the Chloroplast Genome of Adiantum malesianum (Pteridaceae).

Expansion and contraction (ebb and flow events) of inverted repeat (IR) boundaries occur and are generally considered to be major factors affecting chloroplast (cp) genome size changes. Nonetheless, the Adiantum malesianum cp genome does not seem to follow this pattern. We sequenced, assembled and corrected the A. flabellulatum and A. malesianum cp genomes using the Illumina NovaSeq6000 platform, and we performed a comparative genome analysis of six Adiantum species. The results revealed differences in the IR/SC boundaries of A. malesianum caused by a 6876 bp long rpoB-trnD-GUC intergenic spacer (IGS) in the LSC. This IGS may create topological tension towards the LSC/IRb boundary in the cp genome, resulting in a sequential movement of the LSC genes. Consequently, this leads to changes of the IR/SC boundaries and may even destroy the integrity of trnT-UGU, which is located in IRs. This study provides evidence showing that it is the large rpoB-trnD-GUC IGS that leads to A. malesianum cp genome size change, rather than ebb and flow events. Then, the study provides a model to explain how the rpoB-trnD-GUC IGS in LSC affects A. malesianum IR/SC boundaries. Moreover, this study also provides useful data for dissecting the evolution of cp genomes of Adiantum. In future research, we can expand the sample to Pteridaceae to test whether this phenomenon is universal in Pteridaceae.

An ontogenetic framework for functional studies in the model fern Ceratopteris richardii.

As the sister group to seed plants, ferns are a phylogenetically informative lineage. Functional studies in representatives of the fern lineage are helping bridge the knowledge gap in developmental mechanisms between angiosperms and non-vascular plants. The fern life cycle has the advantage of combining a sizable free-living haploid gametophyte, more amenable for developmental studies than the reduced seed plant gametophyte, with an indeterminate and complex diploid sporophyte. Ceratopteris richardii has long been proposed as a model fern and has recently become tractable due to stable transgenesis and increasing genomic resources, allowing researchers to test explicit questions about gene function in a fern for the first time. As with any model system, a detailed understanding of wild-type morphology and a staged ontogeny are indispensable for the characterization of mutant phenotypes resulting from genetic manipulations. Therefore, the goal of this study is to provide a unified reference ontogeny for this emerging model fern as a tool for comparative evolutionary and developmental studies. It complements earlier research by filling gaps in major stages of development of the haploid gametophyte and diploid sporophyte generations, and provides additional descriptions of the shoot apical meristem and early leaf development. This resource is meant to facilitate not only studies of candidate genes within C. richardii, but also broader ontogenetic comparisons to other model plants.

Molecular Evolution of Auxin-Mediated Root Initiation in Plants.

The root originated independently in euphyllophytes (ferns and seed plants) and lycophytes; however, the molecular evolutionary route of root initiation remains elusive. By analyses of the fern Ceratopteris richardii and seed plants, here we show that the molecular pathway involving auxin, intermediate-clade WUSCHEL-RELATED HOMEOBOX (IC-WOX) genes, and WUSCHEL-clade WOX (WC-WOX) genes could be conserved in root initiation. We propose that the "auxin>IC-WOX>WC-WOX" module in root initiation might have arisen in the common ancestor of euphyllophytes during the second origin of roots, and that this module has further developed during the evolution of different root types in ferns and seed plants.

Timing of meristem initiation and maintenance determines the morphology of fern gametophytes.

The alternation of generations in land plants occurs between the sporophyte phase and the gametophyte phase. The sporophytes of seed plants develop self-maintained, multicellular meristems, and these meristems determine plant architecture. The gametophytes of seed plants lack meristems and are heterotrophic. In contrast, the gametophytes of seed-free vascular plants, including ferns, are autotrophic and free-living, developing meristems to sustain their independent growth and proliferation. Compared with meristems in the sporophytes of seed plants, the cellular mechanisms underlying meristem development in fern gametophytes remain largely unknown. Here, using confocal time-lapse live imaging and computational segmentation and quantification, we determined different patterns of cell divisions associated with the initiation and proliferation of two distinct types of meristems in gametophytes of two closely related Pteridaceae ferns, Pteris vittata and Ceratopteris richardii. Our results reveal how the simple timing of a switch between two meristems has considerable consequences for the divergent gametophyte morphologies of the two ferns. They further provide evolutionary insight into the function and regulation of gametophyte meristems in seed-free vascular plants.

A drought-driven model for the evolution of obligate apomixis in ferns: evidence from pellaeids (Pteridaceae).

PREMISE: Xeric environments impose major constraints on the fern life cycle, yet many lineages overcome these limitations by evolving apomixis. Here, we synthesize studies of apomixis in ferns and present an evidence-based model for the evolution and establishment of this reproductive strategy, focusing on genetic and environmental factors associated with its two defining traits: the production of "unreduced" spores (n = 2n) and the initiation of sporophytes from gametophyte tissue (i.e., diplospory and apogamy, respectively). METHODS: We evaluated existing literature in light of the hypothesis that abiotic characteristics of desert environments (e.g., extreme diurnal temperature fluctuations, high light intensity, and water limitation) drive the evolution of obligate apomixis. Pellaeid ferns (Cheilanthoideae: Pteridaceae) were examined in detail, as an illustrative example. We reconstructed a plastid (rbcL, trnG-trnR, atpA) phylogeny for the clade and mapped reproductive mode (sexual versus apomictic) and ploidy across the resulting tree. RESULTS: Our six-stage model for the evolution of obligate apomixis in ferns emphasizes the role played by drought and associated abiotic conditions in the establishment of this reproductive approach. Furthermore, our updated phylogeny of pellaeid ferns reveals repeated origins of obligate apomixis and shows an increase in the frequency of apomixis, and rarity of sexual reproduction, among taxa inhabiting increasingly dry North American deserts. CONCLUSIONS: Our findings reinforce aspects of other evolutionary, physiological, developmental, and omics-based studies, indicating a strong association between abiotic factors and the establishment of obligate apomixis in ferns. Water limitation, in particular, appears critical to establishment of this reproductive mode.

Cryptic diversity in the model fern genus Ceratopteris (Pteridaceae).

Cryptic species are present throughout the tree of life. They are especially prevalent in ferns, because of processes such hybridization, polyploidy, and reticulate evolution. In addition, the simple morphology of ferns limits phenotypic variation and makes it difficult to detect cryptic species. The model fern genus Ceratopteris has long been suspected to harbor cryptic diversity, in particular within the highly polymorphic C. thalictroides. Yet no studies have included samples from throughout its pan-tropical range or utilized genomic sequencing, making it difficult to assess the full extent of cryptic variation within this genus. Here, we present the first multilocus phylogeny of the genus using reduced representation genomic sequencing (RADseq) and examine population structure, phylogenetic relationships, and ploidy level variation. We recover similar species relationships found in previous studies, find support for the cryptic species C. gaudichaudii as genetically distinct, and identify novel genomic variation within two of the mostly broadly distributed species in the genus, C. thalictroides and C. cornuta. Finally, we detail the utility of our approach for working on cryptic, reticulate groups of ferns. Specifically, it does not require a reference genome, of which there are very few available for ferns. RADseq is a cost-effective way to work with study groups lacking genomic resources, and to obtain the thousands of nuclear markers needed to untangle species complexes.

Positive root pressure is critical for whole-plant desiccation recovery in two species of terrestrial resurrection ferns.

Desiccation-tolerant (DT) organisms can lose nearly all their water without dying. Desiccation tolerance allows organisms to survive in a nearly completely dehydrated, dormant state. At the cellular level, sugars and proteins stabilize cellular components and protect them from oxidative damage. However, there are few studies of the dynamics and drivers of whole-plant recovery in vascular DT plants. In vascular DT plants, whole-plant desiccation recovery (resurrection) depends not only on cellular rehydration, but also on the recovery of organs with unequal access to water. In this study, in situ natural and artificial irrigation experiments revealed the dynamics of desiccation recovery in two DT fern species. Organ-specific irrigation experiments revealed that the entire plant resurrected when water was supplied to roots, but leaf hydration alone (foliar water uptake) was insufficient to rehydrate the stele and roots. In both species, pressure applied to petioles of excised desiccated fronds resurrected distal leaf tissue, while capillarity alone was insufficient to resurrect distal pinnules. Upon rehydration, sucrose levels in the rhizome and stele dropped dramatically as starch levels rose, consistent with the role of accumulated sucrose as a desiccation protectant. These findings provide insight into traits that facilitate desiccation recovery in dryland ferns associated with chaparral vegetation of southern California.

Infraspecific diversification of the star cloak fern (Notholaena standleyi) in the deserts of the United States and Mexico.

PREMISE: Not all ferns grow in moist and shaded habitats. One well-known example is Notholaena standleyi, a species that thrives in deserts of the southwestern United States and Mexico. This species exhibits several "chemotypes" that differ in farina (flavonoid exudates) color and chemistry. By integrating data from molecular phylogenetics, cytology, biochemistry, and biogeography, we circumscribed the major evolutionary lineages within N. standleyi and reconstructed their diversification histories. METHODS: Forty-eight samples were selected from across the geographic distribution of N. standleyi. Phylogenetic relationships were inferred using four plastid and five nuclear markers. Ploidy levels were inferred using spore sizes calibrated by chromosome counts, and farina chemistry was compared using thin-layer chromatography. RESULTS: Four clades are recognized, three of which roughly correspond to previously recognized chemotypes. The diploid clades G and Y are found in the Sonoran and Chihuahuan deserts, respectively; they are estimated to have diverged in the Pleistocene, congruent with the postulated timing of climatological events separating these two deserts. Clade P/YG is tetraploid and partially overlaps the distribution of clade Y in the eastern Chihuahuan Desert. It is apparently confined to limestone, a geologic substrate rarely occupied by members of the other clades. The cryptic (C) clade, a diploid group known only from southern Mexico and highly disjunct from the other three clades, is newly recognized here. CONCLUSIONS: Our results reveal a complex intraspecific diversification history of N. standleyi, traceable to a variety of evolutionary drivers including classic allopatry, parapatry with or without changes in geologic substrate, and sympatric divergence through polyploidization.

Incorporation of amino moiety to alepterolic acid improve activity against cancer cell lines: Synthesis and biological evaluation.

Aleuritopteris argentea (S. G. Gmél.) Fée is a medicinal fern consisting of an ent-labdane diterpene, i.e. alepterolic aicd, as the major metabolite. We recently isolated grams of alepterolic acid from A. argentea enabling subsequent structural modification. By incorporation of amino moiety to alepterolic acid, fifteen amide derivatives were synthesized, characterized, and further biological evaluated regarding their activity against four cancer cells and normal human liver cells. The potency of synthesized amides dramatically improved as compared to alepterolic aicd itself. The best hit (compound 11) inhibits HeLa cells with an IC50 of 7.39 ± 0.80 µM, and is nearly nontoxic to normal cells. Compound 11 exhibits an inhibitory effect on the colony forming ability of the four cancer cells, especially of HeLa cells. Moreover, it induces apoptosis of HeLa cells by decreasing mitochondrial membrane potential and altering expression of apoptosis-associated proteins. Release of cytochrome c, activation of caspases-3, caspases-9 and alteration of Bax/Bcl-2 balance was detected in the biological assays. These results imply that compound 11 can inhibit the proliferation of cervical cancer cell line HeLa and induce apoptosis through the mitochondrial pathway. These findings encourage further rational structural modification of 15- carboxyl group of alepterolic acid.

Tolerance mechanism of cadmium in Ceratopteris pteridoides: Translocation and subcellular distribution.

Hydroponic experiment was conducted to investigate the biochemical responses and accumulation behaviour of cadmium (Cd) in aquatic fern, Ceratopteris pteridoides, under four different levels of exposure. Plants were grown in 10 µM (CdT1), 20 µM (CdT2), 40 µM (CdT3) and 60 µM (CdT4) concentrations of Cd for 12 consecutive days and Cd accumulation in different plant parts, cell levels and growth medium was estimated. In C. pteridoides, Cd removal kinetics was best described by pseudo-second-order kinetic model. Increased accumulation of Cd in the plants was detected in a concentration dependent manner with maximum under 60 µM of Cd (CdT4) exposure (191.38 mg kg-1, 186.19 mg kg-1 and 1316.34 mg kg-1 in leaves, stems and roots, respectively). Cell wall of C. pteridoides is identified as crucial Cd storage site with the highest (28-69%) accumulation followed by organelles (14-44%) and soluble fraction (6-46%). Increased leaf proline, malondialdehyde (MDA) and protein content with significant reduction (P < 0.05) in chlorophyll concentration and upregulation of antioxidant enzymes catalase (CAT), guaiacol peroxidase (POD) and superoxide dismutase (SOD) reveals the presence of Cd resistance mechanism in C. pteridoides. Calculated higher (>1) bioconcentration factor (BCF) and lower (<1) translocation factor (TF) values evinced the suitability of C. pteridoides in Cd phytostabilization rather than phytoextraction.

Meristem development and activity in gametophytes of the model fern, Ceratopteris richardii.

Ceratopteris richardii is a model fern species widely used to analyze various developmental processes and their regulation in gametophytes. The form of mature C. richardii gametophytes depends on the activity of the marginal meristem, but knowledge on meristem formation and structure is limited. Therefore, we analyzed cellular events accompanying the development of gametophytes using cell lineage and proliferation analyses to explain the establishment and functioning of the marginal meristem. We show that: i) gametophytes are devoid of the apical initial cell or the apical cell-based meristem in the early developmental stages; ii) the cells that are predestined to form the marginal meristem divide according to a stable pattern; iii) only one transient initial cell is present in the marginal meristem, and the selection of a new functioning initial cell is related to a stable sequence of its divisions. Our results contribute to a better understanding of the developmental events underlying gametophyte growth and marginal meristem functioning in Ceratopteris. The principles, which were established in this study and enabled the identification of functioning initial cells, can be applied to analyze genetic and/or physiological mechanism(s) governing meristem maintenance in vascular plants, both in developmental and evolutionary contexts.