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‘Dust seeds’ with undifferentiated embryos and their germination in mycoheterotrophic Monotropoideae (Ericaceae)
Abstract
‘Dust seeds’ with an undifferentiated (organless) embryo are known to be produced by mycoheterotrophic species (MH) in nine families of angiosperms. However, aside from the numerous studies on seed germination of orchids, relatively little is known about germination in MH families. In the Ericaceae, some degree of mycoheterotrophy (full, partial or initial) and dust seeds with an undifferentiated embryo occur in all species in the three tribes of Monotropoideae, the only subfamily of Ericaceae with this combination of characters. In most species, the seed is <0.90 mm in the greatest dimension, the endosperm is absent ( Pityopus ) or consists of few to many (30–40) cells, and the embryo is minute, consisting of as few as two cells in Monotropa . Germination in Monotropoideae is monopolar, with only the radicular pole of the embryo participating in germination. Thus, germination polarity differs from that of the dust seeds of orchids in which only the plumular pole of the embryo (protocorm) participates in germination. The dust seeds in Monotropoideae require the presence of fungi, either direct contact with a fungus or the presence of a diffusible substance therefrom, to germinate (symbiotic germination). Recently, representatives of the four genera of tribe Pyroleae have been successfully germinated asymbiotically in vitro . We present a broad overview of dust-size seeds in angiosperms and conclude that they should be subdivided into at least two major categories.
... Plants have developed various strategies to ensure seed germination and seedling survival (Hoyle et al., 2015); dust seed production is arguably one of the most intriguing of these strategies (Eriksson and Kainulainen, 2011;Hynson et al., 2013a). Owing to their limited carbohydrate reserves, dust seeds with a minute undifferentiated embryo depend on external carbon sources to support their germination (Baskin and Baskin, 2020). ...
... Little is known about germination in AM mycoheterotrophic plants (Baskin and Baskin, 2020), although decades ago, Leake (1994) stated that further research is required to determine the role of fungi and environmental conditions that are necessary for seed germination of mycoheterotrophic species. To the best of our knowledge, this is the first study to identify fungal identities at the seedling stage in AM fully mycoheterotrophic plants. ...
Plants producing dust seeds often meet their carbon demands by exploiting fungi at the seedling stage. This germination strategy (i.e., mycoheterotrophic germination) has been investigated among orchidaceous and ericaceous plants exploiting Ascomycota or Basidiomycota. Although several other angiosperm lineages have evolved fully mycoheterotrophic relationships with Glomeromycota, the fungal identities involved in mycoheterotrophic germination remain largely unknown. Here, we conducted in situ seed baiting and high‐throughput DNA barcoding to identify mycobionts associated with seedlings of Burmannia championii (Burmanniaceae: Dioscoreales) and Sciaphila megastyla (Triuridaceae: Pandanales), which have independently evolved full mycoheterotrophy. Subsequently, we revealed that both seedlings and adults in B. championii and S. megastyla predominantly associate with Glomeraceae. However, mycorrhizal communities are somewhat distinct between seedling and adult stages, particularly in S. megastyla. Notably, the dissimilarity of mycorrhizal communities between S. megastyla adult samples and S. megastyla seedling samples is significantly higher than that between B. championi adult samples and S. megastyla adult samples, based on some indices. This pattern is possibly due to both mycorrhizal shifts during ontogenetic development and convergent recruitment of cheating‐susceptible fungi. The extensive fungal overlap in two unrelated mycoheterotrophic plants indicates that both species convergently exploit specific AM fungal phylotypes. This article is protected by copyright. All rights reserved.
... A majority of orchids typically produce millions of dust-like, tiny seeds per capsule [2,3], which are devoid of endosperm and hence lack nutrient resources for seed germination [2,4]. Thus, orchid seeds are dependent on external nutrition provided by seed sgOMFs (see Glossary) for germination and subsequent seedling growth [5][6][7][8][9][10][11]. In partnership with sgOMFs, the minuscule reserveless seeds comprising only 80-300 undifferentiated embryonic cells can develop into seedlings within less than 1 month in most orchids [12,13]. ...
... We acknowledged that the calculation method for seed's δ 13 C values and thus %C dF can mislead the extent of mycorrhizal dependencies. However, Py. japonica produces minute-sized dust seeds with a limited endosperm (Takahashi 1993) as with, similar to other pyroloids (Johansson et al. 2014;Baskin and Baskin 2021) and we used only seed fractions devoid of capsules. During the fruiting season, mycorrhizal formation of Py. japonica was higher than that in any other season (Matsuda et al 2012) inferring intimate nutrient exchange, whose pattern was unlike that of an orchid (Gonneau et al. 2014). ...
Pyrola japonica , an Ericaceae, is a mixotroph growing on forest floors, obtaining carbon (C) from both photosynthetic and root-associated mycorrhizal fungal pathways. The mycorrhizal community structures of the plant are well characterised and are dominated by Russulaceae fungi. However, the mechanism of its C acquisition is not well understood. The aim of this study was to identify mycorrhizal fungal communities that are directly involved in C acquisition. We repeatedly applied a fungicide (Benomyl) solution to soils around P. japonica plants in a broad-leaved forest in central Japan to disturb fungal associations near their roots. After fungicide treatment, P. japonica roots were collected and subjected to next-generation sequencing, focusing on the ITS2 region, to infer taxonomic identities. The leaves and seeds of the plants were analysed for C stable isotope ratios. The rate of mycorrhizal formations and α-diversity did not significantly change by the fungicide treatments. Irrespective of the treatments, more than 80% of the detected mycorrhizal taxa were assigned to Russulaceae. For δ ¹³ C values, leaves and seeds in the fungicide were significantly lower than those of the other treatments. Our results suggest that the fungicide did not affect mycorrhizal communities, but likely disturbed mycorrhizal fungal pathways via extraradical hyphae, which may result in a relative increase in its own photosynthetic pathways.
Impermeable seed/fruit coats, i.e., physical dormancy (PY), occurs only in several genera belonging to 19 angiosperm families. However, recent reviews on fire ecology have proposed including serotiny under PY and dormancy-broken seeds waiting for germination as ‘imposed secondary dormancy’. Serotiny occurs in 12 angiosperm and gymnosperm families, mutually exclusive from PY families, suggesting no linkage between these two traits. Imposed secondary dormancy essentially refers to the non-dormant seeds waiting for germination, as no dormancy-breaking treatments are required for germination. Understanding the evolutionary and ecological significance of PY is imperative, one of the first steps in this direction is to correctly define the seed traits. In contemporary species, the ability of PY to develop impermeable or permeable coats is under the influence of climate.
Generally, orchids produce dust-like seeds in which endosperm reduction and embryo undifferentiation represent a derived state shared with species in about 11 other plant families. Orchid seeds are proposed to have a special kind of morphological or morphophysiological dormancy. We test this proposition, overcoming several design limitations of earlier studies, specifically that the in vitro germination method for orchid seeds uses pro-oxidants for disinfection and incorporates nitrate in the medium; both ‘treatments’ might contribute to dormancy breaking, potentially confounding judgement on the depth and nature of the dormant state. Seeds of the tropical orchid Dendrobium cruentum Rchb. f., were sown both in vitro , on a nutrient medium, and ex vitro , on plain agar omitting prior disinfection with sodium hypochlorite. Seeds previously stored and fresh seeds were incubated under combinations of vitro conditions, light treatments, constant or alternating temperatures and nitrate concentration. Seeds of D. cruentum are very small but have a large embryo that occupies most of the seed. Over a range of constant temperature seeds germinated to the spherical protocorm stage just as well ex vitro as in vitro . Neither light nor nitrate were prerequisites for ex vitro germination. The ability of D. cruentum seed to germinate in the absence of environmental or chemical stimuli suggests that mature seed can be non-dormant. Our results support the proposition that neither all DUST seed fit a dormancy class nor all orchids produce morphological or morphophysiological seeds. Finally, embryo/seed volume determinations in orchids may prove as valuable in studies on the evolution and ecology of germination and dormancy as embryo:seed ratios in other angiosperm species.
For a successful germination and plant growth, seeds must germinate at the right time. Seeds must become nondormant and must fulfill the seed germination requirements. These requirements include light/dark, moisture, temperature, and other environmental cues (e.g., ethylene, exudate from host roots, or chemicals from fire) in the habitat. Seeds come out from dormancy in response to environmental cues, but depending on the species, they may need to be exposed to a second set of environmental cue to germinate. That is, nondormant seeds require specific temperature and water conditions to germination, and sometimes unfavorable temperature and water conditions will cause seeds to enter secondary dormancy. There are still mysteries about how/what environmental cues help seeds detect the right time/conditions for germination after dormancy is broken. Our knowledge of species-specific conditions is incomplete and further studies are needed.
This review provides a revised and expanded word-formula system of whole-seed primary dormancy classification that integrates the scheme of Nikolaeva with that of Baskin and Baskin. Notable changes include the following. (1) The number of named tiers (layers) in the classification hierarchy is increased from three to seven. (2) Formulae are provided for the known kinds of dormancy. (3) Seven subclasses of class morphological dormancy are designated: ‘dust seeds’ of mycoheterotrophs, holoparasites and autotrophs; diaspores of palms; and seeds with cryptogeal germination are new to the system. (4) Level non-deep physiological dormancy (PD) has been divided into two sublevels, each containing three types, and Type 6 is new to the system. (5) Subclass epicotyl PD with two levels, each with three types, has been added to class PD. (6) Level deep (regular) PD is divided into two types. (7) The simple and complex levels of class morphophysiological dormancy (MPD) have been expanded to 12 subclasses, 24 levels and 16 types. (8) Level non-deep simple epicotyl MPD with four types is added to the system. (9) Level deep simple regular epicotyl MPD is divided into four types. (10) Level deep simple double MPD is divided into two types. (11) Seeds with a water-impermeable seed coat in which the embryo-haustorium grows after germination ( Canna ) has been added to the class combinational dormancy. The hierarchical division of primary seed dormancy into many distinct categories highlights its great diversity and complexity at the whole-seed level, which can be expressed most accurately by dormancy formulae.
Seed exomorphic characters of 32 taxa of Brassicaceae were investigated by LM and SEM. The diagnostic
characterts at the generic and specific level are, seed shape, dimensions, colour, epidermal cells, and seed coat surface
and aspect of anticlinal and periclinal walls. Seed shape among the studied taxa showed wide range of variations.
LM revealed most of the studied seeds vary from globose to oblong-ellipsoid or elongate. Most of the seeds have no
wings except Farsetia aegyptia. SEM investigation at higher magnifications revealed main six types of seed surface
sculpture; reticulate, ocellate, foveate, papillate, stellate and domate. The seed exomorphic criteria obtained from LM
and SEM were analyzed by the STATISCA program package using the UPGMA clustering method. Produced data
facilitate the construction of a dendrogam between the studied taxa. Two groups are represented from the first group
included the taxa of Tribe Arabideae, Lepidieae, Matthioleae, Sisymbrieae, Alysseae, Chamireae, Schizopetaleae,
Stenopetaleae, Drabeae, Euclidieae, Lunarieae, and Streptantheae. The second group included the most commonly
known genera of the tribe Brassiceae
Background:
Cactaceae is the fifth taxonomic group with the highest proportion of threatened species. One way to contribute to the preservation of this family is to understand the processes that promote seed germination.
Questions:
How common is dormancy and seed banks in Cactaceae? Are there general patterns in cacti germination response to temperature, light, water, salinity, phytohormones, hydration/dehydration cycles, mechanical or chemical scarification?
Data description:
A total of 333 studies on cactus germination with information on 409 taxa.
Study site and dates:
since 1939 to January 2020.
Methods:
A search of scientific articles in Google Scholar was performed with the words Cactaceae, cacti and cactus, in combination with various matters on germination in English, Spanish and Portuguese.
Results:
The main germination studies in cactus deal with photoblasticism (275 taxa), temperature (205 taxa) and seed longevity (142 taxa). Other lines of study in cactus germination (e.g., desiccation tolerance, vivipary, phytohormones, mechanical or chemical scarification, in vitro germination, hydration/dehydration cycles, water and saline stress, serotiny, storage in cold, high temperature tolerance and soil seed bank) include between 14 and 65 taxa. Cacti have only physiological dormancy and optimal germination for most species occur between 20 and 30 °C.
Conclusions:
Mexico, Brazil and Argentina are the three leading countries in the study of cactus germination.
Premise:
Difficulties in comparing extremely divergent features in fully mycoheterotrophic plants with those in closely related chlorophyllous plants have complicated attempts to reveal the evolutionary patterns and processes of fully mycoheterotrophic plants. Albino mutants of partially mycoheterotrophic plants, generally observed in Orchidaceae, have provided an ideal model for investigating the evolution of mycoheterotrophy within similar genetic backgrounds. In 2018, we found a putative albino population of Pyrola (Ericaceae). Here we aimed to reveal the identity of the albino pyroloid and confirm its fully mycoheterotrophic status.
Methods:
To reveal the putative albino pyroloid's identity, we examined its morphology and sequenced its chloroplast DNA. In addition, we assessed the trophic status of the putative albino pyroloid by analyzing chlorophyll fluorescence, chlorophyll concentration, and natural 13 C and 15 N abundances.
Results:
We identified albino individuals as P. japonica-otherwise a partially mycoheterotrophic species. We confirmed their albino status by their considerably lower chlorophyll fluorescence and concentrations than those of sympatrically occurring chlorophyllous plants. 13 C abundance in the albino individuals was significantly higher than in the green individuals of P. japonica.
Conclusions:
This first report of albino mutants from partially mycoheterotrophic species in angiosperms other than orchids will play a valuable role in further studies focused on mycoheterotrophy. For instance, their δ13 C and δ15 N values represent a reference for fully mycoheterotrophic plants in Pyrola. Our findings also indicate the strong dependence of some leafy Pyrola species on fungal C during their entire life cycle.
Information about seed dormancy cycling and germination in relation to temperature and moisture conditions in the natural environment is important for the conservation and restoration of rare species, including Begonia guishanensis and Paraisometrum mileense , two sympatric perennial limestone (karst) species. Dry afterripening (DAR) and wet and dry (WD) cycles at 15/5 and 25/15°C as well as moist chilling (MC) at 15/5°C were used to mimic the natural environment at different times of the year. A field experiment was conducted to monitor seasonal changes in germination responses of the seeds. About 40–65% of B. guishanensis and 5% of P. mileense seeds were dormant at maturity. DAR at 25/15 and 15/5°C as well as MC and WD cycles at 15/5°C alleviated dormancy for B. guishanensis but not P. mileense , and WD cycles at 25/15°C induced a deeper conditional dormancy for both species. Seeds of B. guishanensis exhibited dormancy cycling in the field, with increased dormancy under natural WD cycles at relatively high temperatures during the transition from the dry to the wet season in April to May and decreased dormancy during the wet season from June to October. KNO 3 mitigated the dormancy-inducing effect of both artificial and natural WD cycles at relatively high temperatures for B. guishanensis. The field experiment indicated that seeds of B. guishanensis may be able to form a persistent soil seed bank, while almost all seeds of P. mileense germinate at the beginning of the wet season in the field.
Seed morphology of two distinct european species of Erica L. (Ericaceae). Erica spiculifolia is a distinct species within the genus Erica, considered by some authors as part of a monospecific genus: Bruckenthalia. The second species studied, E. umbellata, is the only European species of section Pyronium. Seed morphology of the two species was studied by means of SEM techniques. Seeds from different populations were used. Characters concerning size and shape of seeds, primary and secondary ornamentation were observed and measured. The seeds of E. spiculifolia are close to those of other species within the genus, supporting the inclusion in Erica. E. umbellata seeds have some exclusive characters within the European species of the genus: a verrucate secondary ornamentation and surface cells with “omega type” cell boundaries. The systematics of genus Erica is still unresolved, and the taxonomic position of these species has to be clarified. As found in previous studies, seed characters provide useful taxonomic characters that should be used in the interpretation of the taxonomic position of these species within Erica.Key words. Erica, Ericaceae, seed morphology, SEM, testa sculpture, taxonomy.RESUMEN. Morfología de las semillas de dos especies europeas de Erica L. (Ericaceae). Erica spiculifolia es una especie con características únicas dentro del género Erica en Europa, considerada por algunos autores como perteneciente al género monoespecífico Bruckenthalia. La segunda especie estudiada, E. umbellata, es la única especie de la sección Pyronium dentro del núcleo norte del género. Se estudia la morfología de las semillas mediante la fotografía de microscopía electrónica. Se miden semillas de diferentes poblaciones de cada especie. Se estudian y miden diversos caracteres del tamaño y la forma de las semillas, la ornamentación primaria y secundaria. Las semillas de E. spiculifolia coinciden en la mayor parte de los caracteres con otras especies del género, lo que apoya su pertenencia a Erica. Las semillas de E. umbellata presentan algunos caracteres exclusivos que permiten diferenciarla de otras especies europeas del género: una ornamentación secundaria verrucosa y las uniones entre las células de la testa de “tipo omega”. La taxonomía del género Erica no está aún resuelta, y la posición sistemática de estas especies debe clarificarse. Como se desprende de éste y otros estudios publicados, la morfología de las semillas aportan caracteres de diagnóstico que deben utilizarse para una correcta interpretación de las relaciones taxonómicas dentro del género.Palabras clave. Erica, Ericaceae, morfología de las semillas, M.E.B., ornamentación de la testa, taxonomía
Seed morphology underpins many critical biological and ecological processes, such as seed dormancy and germination, dispersal, and persistence. It is also a valuable taxonomic trait that can provide information about plant evolution and adaptations to different ecological niches. This study characterised and compared various seed morphological traits, i.e., seed and pod shape, seed colour and size, embryo size, and air volume for six orchid species; and explored whether taxonomy, biogeographical origin, or growth habit are important determinants of seed morphology. We investigated this on two tropical epiphytic orchid species from Indonesia (Dendrobium strebloceras and D. lineale), and four temperate species from New Zealand, terrestrial Gastrodia cunnninghamii, Pterostylis banksii and Thelymitra nervosa, and epiphytic D. cunninghamii. Our results show some similarities among related species in their pod shape and colour, and seed colouration. All the species studied have scobiform or fusiform seeds and prolate-spheroid embryos. Specifically, D. strebloceras, G. cunninghamii, and P. banksii have an elongated seed shape, while T. nervosa has truncated seeds. Interestingly, we observed high variability in the micro-morphological seed characteristics of these orchid species, unrelated to their taxonomy, biogeographical origin, or growth habit, suggesting different ecological adaptations possibly reflecting their modes of dispersal.
The widely accepted “endozoochory syndrome” is assigned to angiosperm diaspores with a fleshy, attractive tissue and implies the existence of adaptations for protection against digestion during gut passage. This syndrome has led diaspore fleshiness to be emphasized as the exclusive indicator of endozoochory in much of the ecology and biogeography research. Crucially, however, endozoochory in nature is not limited to frugivory, and diaspores without “external flesh” are commonly dispersed, often over long distances, via birds and mammals by granivory. A key question is: are such diaspores somehow less prepared from an architectural point of view to survive gut passage than fleshy diaspores? To answer this question, we selected 11 European angiosperm taxa that fall outside the classical endozoochory syndrome yet are known to be dispersed via endozoochory. We studied their seed coat/pericarp morphology and anatomy both before and after gut passage through granivorous waterfowl, and determined their seed survival and germinability. We found no fundamental differences in the mechanical architecture of the seed coat and pericarp between these plants dispersed by granivory and others dispersed by frugivory. Neither diaspore traits per se, nor dormancy type, were strong predictors of diaspore survival or degree of damage during gut passage through granivores, or of the influence of gut passage on germinability. Among our 11 taxa, survival of gut passage is enabled by the thick cuticle of the exotesta or epicarp; one or several lignified cell layers; and diverse combinations of other architectural elements. These protection structures are ubiquitous in angiosperms, and likely to have evolved in gymnosperms. Hence, many angiosperm diaspores, dry or fleshy, may be pre-adapted to endozoochory, but with differing degrees of specialization and adaptation to dispersal mechanisms such as frugivory and granivory. Our findings underline the broad ecological importance of “non-classical endozoochory” of diaspores that lack “external flesh”.
Orchids are globally distributed, a feature often attributed to their tiny dustlike seeds. They were ancestrally terrestrial but in the Eocene expanded into tree canopies, with some lineages later returning to the ground, providing an evolutionarily replicated system. Because seeds are released closer to the ground in terrestrial species than in epiphytic ones, seed traits in terrestrials may have been under selective pressure to increase seed dispersal efficiency. In this study, we test the expectations that seed airspace-a trait known to increase seed flotation time in the air-is (i) larger in terrestrial lineages and (ii) has increased following secondary returns to a terrestrial habit. We quantified and scored 20 seed traits in 121 species and carried out phylogenetically informed analyses. Results strongly support both expectations, suggesting that aerodynamic traits even in dust seeds are under selection to increase dispersal ability, following shifts in average release heights correlated with changes in habit.
p> Background : Podostemaceae are extremely susceptible to local extinction by habitat loss. Since ~70 % of the river systems in Mexico show some degree of water contamination, it is relevant to generate information about seed storage and germination behavior to design germplasm conservation strategies ( e.g ., ex situ seed banks) of Mexican podostemads.
Hypotheses : Seed germination decreases as seed storage time increases. Further, light quality, temperature and collection site influence similarly the germination response of both species.
Studied species : Marathrum foeniculaceum Humb. & Bonpl., Noveloa coulteriana (Tul.) C. Philbrick
Study site and years of study : 13 different seeds collections (1996-2013), at four locations in the rivers Horcones and Arroyo del Rincon Jalisco, México.
Methods : A germination chamber experiment was performed to evaluate the effect of temperature, light quality and storage time on the germination of both species.
Results : Seeds lose viability after nine years of storage. In both species, the time to reach the highest Accumulated Germination Percentage (AGP) was faster in seeds of one-two yr compared to seeds of six-seven yr. N. coulteriana have significant differences in Final Germination Percentage (FGP) between collection rivers. Storage time affects AGP of N. coulteriana more than in M. foeniculaceum.
Conclusions : Both species can form ex situ seed banks up to 8 yr age in paper bags storage. N. coulteriana is more susceptible to variation in storage conditions compared to M. foeniculaceum . Collection site affect seed germination after storing. Long-term conventional ex situ seed germination storage is not a viable strategy to conserve germplasm of Podostemaceae.</p
Laboratory and greenhouse experiments were conducted to determine the effect of environmental factors on the germination and emergence of five species of Potentilla L. All of the species we studied differed in their germination requirements, and these could be related to their habitat/ecology. For all species, completion of germination was the highest at 25/15 °C with a 14 h photoperiod. Seeds of Potentilla argentea L. and P. inclinata Vill. completed germination immediately after ripening while seeds of P. aurea Borkh., P. incana P.Gaertn., B.Mey. & Scherb., and P. reptans L. needed a 16-week period of cold stratification to break dormancy. GA3 treatment did not substitute for cold stratification. The seeds of all species did not complete germination in darkness and showed maximal emergence on the soil surface, which suggests the formation of a persistent seed bank. Completion of germination was inhibited by decreasing osmotic potential and increasing salt concentration. The seeds of all species we studied can complete germination in both acidic and alkaline soils. These results suggest that under field conditions, if moisture and (or) salinity are not limiting factors and a seed is located on the soil surface, completion of germination of nondormant species (P. argentea and P. inclinata) is possible any month of the growing season.
The seeds of most heterotrophic plants, commonly referred to as dust seeds, are typically dispersed in the air like dust particles. Therefore, little attention has been paid to how seeds of heterotrophic plants are dispersed, owing to the notion that wind dispersal is the dominant strategy. However, inconspicuous but fleshy, indehiscent fruit can be observed in distantly related plants that have independently evolved full heterotrophy.
Here I investigated the seed dispersal system in three unrelated fully heterotrophic plants with fleshy, indehiscent fruits ( Yoania amagiensis , Monotropastrum humile and Phacellanthus tubiflorus ) by direct observation, a differential exclusion experiment of fruit feeders and investigation on seed viability through the digestive tract.
The present study revealed that camel crickets are the major seed disperser in three achlorophyllous plants in the study population. This represents the first evidence of seed dispersal by camel crickets in any angiosperm species.
These heterotrophic plants grow in the understorey of densely vegetated forests where wind is probably an ineffective seed dispersal agent. Life‐history traits of the achlorophyllous plants associated with heterotrophic lifestyles, such as colonization of dark understorey habitats and dust seeds, could facilitate independent recruitment of the novel endozoochorous seed dispersal system by camel crickets.
Determining the extent of mycoheterotrophy (MH) in plants, primarily through the use of stable isotope methods, has gained considerable attention in the last decade. The aim of this study was to characterize the rates of photosynthesis (PS) and several gas-exchange parameters, as well as stable carbon isotope composition (δ¹³C) of partially mycoheterotrophic (PMH) Pyroleae compared with autotrophic reference species of Ericaceae. An end-member mixing model was applied to δ¹³C, deriving estimates of % C gained via fungi (CDF). The δ¹³C was significantly enriched for Orthilia secunda and Pyrola chlorantha (relative to autotrophs) resulting in estimates of CDF ranging from 13.8% to 20.8%. Despite significantly lower PS rates for O.secunda and P.chlorantha, as well as lower conductance and transpiration, there were no significant differences in the Ci:Ca ratios across all of the species, suggesting that the C isotope inferences for these two species were reflective of fungal C gains. By contrast, results for all of the variables indicated primarily autotrophic C nutrition for Chimaphila umbellata. Further studies, such as isotope labelling experiments or assessments of biochemical constraints to autotrophy, may resolve the uncertainties in these species, allowing more accurate understanding of the complex nutritional mode of these plants.
Eight Hypericum species are native to Poland: H. elegans Stephan ex Willd., H. hirsutum L., H. humifusum L., H. maculatum Crantz, H. montanum L., H. perforatum L., H. pulchrum L., and H. tetrapterum Fr. Only seeds of H. elegans were investigated in detail in Poland before, so here we present results of qualitative and quantitative analyses of seed morphology of the other 7 species, based on characters like seed length, width, and shape, seed coat sculpture, shape of epidermal cells of the testa, and number of epidermal cells along the seed axis. The results show that seeds of the studied species are small, 0.56-1.15 mm long and 0.26-0.49 mm wide. In SEM images, seed coat sculpture is reticulate in 5 species, papillate in H. hirsutum, and cup-shaped in H. pulchrum. The differences are caused by the varied final development of the testa epidermis, which constitutes the outer layer of the seed coat. The mean number of epidermal cells along the seed axis ranges from 22 to 33. Results of cluster analysis, based on the agglomeration method and including also published data on seeds of H. elegans, show that the variation in the investigated characters of seeds is reflected in the taxonomic division of the genus into sections.
Knowledge about the mycorrhizal root traits of plants is critical for understanding ecosystem processes from landscape to global scale. In spite of >130 years of research, information about the mycorrhizal status of plants is scant for multiple taxonomic groups and geographic regions. By critically evaluating published information about mycorrhizal associations from the plant perspective and integrating this information with plant phylogeny, we assigned altogether 335 ectomycorrhizal (EcM) plant genera (ca. 8500 species) into 30 monophyletic lineages. Considering low representation of EcM habit in Gnaphalieae, Myrtoideae, Goodeniaceae and Acacia s.str., we estimate that approx. 6000–7000 plant species from 250 to 300 genera are able to establish EcM symbiosis. We nominated further 22 plant genera (comprising 76 species) that may potentially exhibit EcM habit based on their close phylogenetic proximity to these known EcM groups. EcM plants thus constitute 1.7–2.4% of all accepted higher plant (Embryophyta) species. EcM habit has evolved and persisted two times in various groups of gymnosperms and 28 times in angiosperms over a vast time interval since the Early Jurassic. In addition to these multiple gains, we also recovered several potential losses of EcM habit in Fagales, two groups of Fabales, two groups of Asterales and Myrtoideae that could be attributed to shifts to association with nitrogen-fixing bacteria, shrubby or herbaceous life form or wetland habitat. There is still much confusion about the mycorrhizal status in multiple families where conflicting reports exist and incorrect assignments have rooted themselves deeply in the literature. We also discuss the reasons for conflicting reports and point to further research needs in critical taxa to improve our overall understanding about the evolution of ectomycorrhizal symbiosis in plants.
Background and aims:
In temperate forests, some green plants, namely pyroloids (Pyroleae, Ericaceae) and some orchids, independently evolved a mode of nutrition mixing photosynthates and carbon gained from their mycorrhizal fungi (mixotrophy). Fungal carbon is more enriched in 13 C than photosynthates, allowing estimation of the proportion of carbon acquired heterotrophically from fungi in plant biomass. Based on 13 C enrichment, mixotrophic orchids have previously been shown to increase shoot autotrophy level over the growth season and with environmental light availability. But little is known about the plasticity of use of photosynthetic versus fungal carbon in pyroloids.
Methods:
Plasticity of mixotrophy with leaf age or light level (estimated from canopy openness) was investigated in pyroloids from three Estonian boreal forests. Bulk leaf 13 C enrichment of five pyroloid species was compared with that of control autotrophic plants along temporal series (over one growth season) and environmental light gradients ( n =405 samples).
Key results:
Mixotrophic 13 C enrichment was detected at studied sites for Pyrola chlorantha and Orthilia secunda (except at one site for the latter), but not for Chimaphila umbellata , Pyrola rotundifolia and Moneses uniflora . Enrichment with 13 C did not vary over the growth season or between leaves from current and previous years. Finally, although one co-occurring mixotrophic orchid showed 13 C depletion with increasing light availability, as expected for mixotrophs, all pyroloids responded identically to autotrophic control plants along light gradients.
Conclusions:
A phylogenetic trend previously observed is further supported: mixotrophy is rarely supported by 13 C enrichment in the Chimaphila + Moneses clade, whereas it is frequent in the Pyrola + Orthilia clade. Moreover, pyroloid mixotrophy does not respond plastically to ageing or to light level. This contrasts with the usual view of a convergent evolution with orchids, and casts doubt on the way pyroloids use the carbon gained from their mycorrhizal fungi, especially to replace photosynthetic carbon.
Elatine L. contains ca. 25 small, herbaceous, annual species distributed in ephemeral waters in both hemispheres. All species are amphibious and characterized by a high degree of morphological variability. The importance of seed morphology in Elatine taxonomy has been emphasized by many authors. The degree of seed curvature and seed coat reticulation have been traditionally considered very important in recognizing individual species of this genus. Seed morphometric characteristics of 10 Elatine species, including all European native taxa, are provided on the basis of material from two or three populations of each species. A total of 24–50 seeds were studied from each population, altogether 1,260 images were used for the morphometric study. In total, six parameters were measured from SEM pictures: object surface area, profile specific perimeter (object circuit), rectangle of the object (a) length, rectangle of the object (b) width, angle of the seed curvature, and number of pits in the seed coat counted in the middle row. Our study shows that the range of morphological variation of seeds in European species of Elatine is great, both between the species and the populations. Discrimination analysis showed that all six traits significantly differentiate the populations studied (λ = 0.001, p
Xyridaceae comprises the seventh largest monocot family in Brazil, with Xyris L. being the largest and most representative genus there. The most important center of diversity for this genus is the Espinhaço Range in southeastern Brazil, where these plants grow in rocky open fields (campo rupestre), usually on humid or boggy soils. The present work examined the seed germination of Xyris species to evaluate the relationships between the germination requirements and their geographic distribution patterns and the distinct micro-habitats they occupy. Laboratory tests were carried out to evaluate light, temperature, and oxygen restriction effects on the germination of eight Xyris species occurring in the Espinhaço Range. All eight species had small seeds that were intolerant of high temperatures (≥35 °C) when imbibed, absolute light requirements for germination, and were able to germinate under hypoxic conditions. The effects of temperature on seed germination do not explain the patterns of geographic distribution nor the endemism seen among the species examined here. Additionally, the occurrence of Xyris species in soils with different water retention capacities cannot be attributed to the capacity of their seeds to germinate under conditions of hypoxia, as the seeds of species that occur on well-drained soils also germinated under low-oxygen condition.
Mycoheterotrophic plants obtain organic carbon from associated mycorrhizal fungi, fully or partially. Angiosperms with this form of nutrition possess exceptionally small ‘dust seeds’ which after germination develop ‘seedlings’ that remain subterranean for several years, fully dependent on fungi for supply of carbon. Mycoheterotrophs which as adults have photosynthesis thus develop from full to partial mycoheterotrophy, or autotrophy, during ontogeny. Mycoheterotrophic plants may represent a gradient of variation in a parasitism-mutualism continuum, both among and within species. Previous studies on plant-fungi associations in mycoheterotrophs have focussed on either germination or the adult life stages of the plant. Much less is known about the fungal associations during development of the subterranean seedlings. We investigated germination and seedling development and the diversity of fungi associated with germinating seeds and subterranean seedlings (juveniles) in five Monotropoideae (Ericaceae) species, the full mycoheterotroph Monotropa hypopitys and the putatively partial mycoheterotrophs Pyrola chlorantha, P. rotundifolia, Moneses uniflora, and Chimaphila umbellata. Seedlings retrieved from seed sowing experiments in the field were used to examine diversity of fungal associates, using pyrosequencing analysis of ITS2 region for fungal identification. The investigated species varied with regard to germination, seedling development and diversity of associated fungi during juvenile ontogeny. Results suggest that fungal host specificity increases during juvenile ontogeny, most pronounced in the fully mycoheterotrophic species, but a narrowing of fungal associates was found also in two partially mycoheterotrophic species. We suggest that variation in specificity of associated fungi during seedling ontogeny in mycoheterotrophs represent ongoing evolution along a parasitism-mutualism continuum. This article is protected by copyright. All rights reserved.
Background and aims:
Recent parsimony-based reconstructions suggest that seeds of early angiosperms had either morphophysiological or physiological dormancy, with the former considered as more probable. The aim of this study was to determine the class of seed dormancy present in Amborella trichopoda, the sole living representative of the most basal angiosperm lineage Amborellales, with a view to resolving fully the class of dormancy present at the base of the angiosperm clade.
Methods:
Drupes of A. trichopoda without fleshy parts were germinated and dissected to observe their structure and embryo growth. Pre-treatments including acid scarification, gibberellin treatment and seed excision were tested to determine their influence on dormancy breakage and germination. Character-state mapping by maximum parsimony, incorporating data from the present work and published sources, was then used to determine the likely class of dormancy present in early angiosperms.
Key results:
Germination in A. trichopoda requires a warm stratification period of at least approx. 90 d, which is followed by endosperm swelling, causing the water-permeable pericarp-mesocarp envelope to split open. The embryo then grows rapidly within the seed, to radicle emergence some 17 d later and cotyledon emergence after an additional 24 d. Gibberellin treatment, acid scarification and excision of seeds from the surrounding drupe tissues all promoted germination by shortening the initial phase of dormancy, prior to embryo growth.
Conclusions:
Seeds of A. trichopoda have non-deep simple morphophysiological dormancy, in which mechanical resistance of the pericarp-mesocarp envelope plays a key role in the initial physiological phase. Maximum parsimony analyses, including data obtained in the present work, indicate that morphophysiological dormancy is likely to be a pleisiomorphic trait in flowering plants. The significance of this conclusion for studies of early angiosperm evolution is discussed.
This chapter reviews the discovery of mixotrophy in mycorrhizal plants, the available data on mixotrophic physiology, and the evolutionary link between mixotrophy and full mycoheterotrophy. In usual mycorrhizal associations, the fungus exploits plant photosynthetic carbon (C) and provides mineral resources as a reward, such as nitrogen (N), phosphorous or water collected in the soil by its mycelium. A variant of mycoheterotrophy occurs in plants that initiate their development as mycoheterotrophic seedlings before turning green at adulthood. This initial mycoheterotrophy is known in several basal plant lineages disseminated by spores, but also in plants that form minute seeds with extremely limited reserves and require fungal C to germinate as mycoheterotrophs, such as orchids. Initial mycoheterotrophy may still fit into a mutualistic framework, since the fungus is rewarded in C when plants are adult. Mixo- and mycoheterotrophic plants offer a fascinating, newly and fully open research area, demonstrating the power of mycorrhizal networks in shaping mycorrhizal networks.
Premise of the study:
Although the evolution of full mycoheterotrophy has attracted many plant researchers, molecular phylogenetic studies that focus on the transition from partial to full mycoheterotrophy are limited to a few taxa. Pyrola japonica sensu lato is an ideal model for examining the evolution of mycoheterotrophy, owing to its variable leaf size, which suggests that the species comprises several transitional stages.
Methods:
To elucidate the molecular and morphological changes that occur during the evolutionary transition between partial and full mycoheterotrophy in P. japonica s.l. from 18 populations in Japan, we estimated a parsimony network of plastid haplotypes based on three noncoding regions, measured the leaf size and scape color of the shoots, and compared morphology among haplotypes.
Key results:
The seven haplotypes exhibited star-like relationships, and at least three divergent haplotypes were associated with differences in morphology. The first was mainly observed in large-leaved and green-scaped populations, whereas the second was observed in extremely small-leaved and reddish-scaped populations, which indicated a high degree of mycoheterotrophy, and the last was detected among mixed populations with both green- and reddish-scaped shoots with intermediate leaf sizes. In addition, the inconsistent association between the haplotypes and morphology suggests a complex relationship.
Conclusions:
Pyrola japonica s.l. has at least three separate genetic lineages that have different leaf morphologies. The genetic lineages and their coexistence could have led to the variable leaf size and suggest the possibility that gene flow from partial to full mycoheterotrophs could reverse the evolutionary transition to full mycoheterotrophy.
Background and Aims Mycoheterotrophy entails plants meeting all or a portion of their carbon (C) demands via symbiotic interactions with root-inhabiting mycorrhizal fungi. Ecophysiological traits of mycoheterotrophs, such as their C stable isotope abundances, strongly correlate with the degree of species’ dependency on fungal C gains relative to C gains via photosynthesis. Less explored is the relationship between plant evolutionary history and mycoheterotrophic plant ecophysiology. We hypothesized that the C and nitrogen (N) stable isotope compositions, and N concentrations of fully and partially mycoheterotrophic species differentiate them from autotrophs, and that plant family identity would be an additional and significant explanatory factor for differences in these traits among species. We focused on mycoheterotrophic species that associate with ectomycorrhizal fungi from plant families Ericaceae and Orchidaceae.
Methods Published and unpublished data were compiled on the N concentrations, C and N stable isotope abundances (δ13C and δ15N) of fully (n = 18) and partially (n = 22) mycoheterotrophic species from each plant family as well as corresponding autotrophic reference species (n = 156). These data were used to calculate site-independent C and N stable isotope enrichment factors (ε). Then we tested for differences in N concentration, 13C and 15N enrichment among plant families and trophic strategies.
Key Results We found that in addition to differentiating partially and fully mycoheterotrophic species from each other and from autotrophs, C and N stable isotope enrichment also differentiates plant species based on familial identity. Differences in N concentrations clustered at the plant family level rather than the degree of dependency on mycoheterotrophy.
Conclusions We posit that differences in stable isotope composition and N concentrations are related to plant family-specific physiological interactions with fungi and their environments.
The mycoheterotrophic genus Epirixanthes Blume is a small genus of Polygalaceae. Here, we describe a new species of Epirixanthes, E. confusa Tsukaya, M. Suleiman and H. Okada, discovered in the mostly unexplored Imbak Canyon, Sabah, Borneo. Along with photographs and illustrations of this new species, a revised key to the genus is presented.
A new classification of Ericaceae is presented based on phylogenetic analyses of nuclear and chloroplast DNA sequence data, morphology, anatomy, and embryology. Eight subfamilies and 20 tribes are recognized. In this classification Epacridaceae are included as Styphelioideae and Empetraceae as tribe Empetreae within the Ericoideae. The herbaceous taxa previously recognized as Pyrolaceae and Monotropaceae by some authors are also included within Ericaceae, in the subfamily Monotropoideae. A key, morphological descriptions, and representative images are provided for all named groups. Two new combinations inKalmia (K. buxifolia andK. procumbens) are made, and three new taxa are described: Oligarrheneae, Richeeae, and Cosmelieae (all within Styphelioideae).
Over the course of evolution, several plant lineages have found ways to obtain water, minerals, and carbohydrates from fungi. Some plants are able exploit fungi to such an extent that they lose the need for photosynthesis. The ability of a plant to live on fungal carbon is known as mycoheterotrophy. This intriguing process has fascinated botanists for centuries, yet many aspects of mycoheterotrophy have remained elusive for a long time. Mycoheterotrophy: The Biology of Plants Living on Fungi explores the biology of mycoheterotrophs, offering general insights into their ecology, diversity, and evolution. Written by renowned experts in the field and bolstered with lavish illustrations and photographs, this volume provides a thematic overview of different aspects of mycoheterotrophy. Comprehensive and readily accessible, Mycoheterotrophy: The Biology of Plants Living on Fungi is a valuable resource for researchers and students who are interested in the process of mycoheterotrophy. © 2013 Springer Science+Business Media New York. All rights are reserved.
Shrubby seablite or lani (Suaeda fruticosa Forssk) is a perennial euhalophyte with succulent leaves, which could be planted on arid-saline lands for restoration and cultivated as a non-conventional edible or cash crop. Knowledge about the impacts of maternal saline environment on seed attributes of this important euhalophyte is lacking. This study investigated the effects of maternal salinity on yield, size and stress tolerance of S. fruticosa seeds. Seedlings of S. fruticosa were grown in a green net house under increasing maternal salinity levels (0, 300, 600 and 900 mM NaCl) until seed production. Total yield, size, stress tolerance and germination of the descended seeds under different maternal saline conditions were examined. Plants grown under saline conditions (300, 600 and 900 mM NaCl) produce a substantially higher quantity of seeds than plants grown under non-saline condition (0 mM NaCl). Low maternal salinity (300 mM NaCl) improves seed size. Seeds produced under all maternal salinity levels display a higher tolerance to low temperature (night/day thermoperiod of 10°C/20°C), whereas seeds produced under 300 mM NaCl maternal saline condition show a better tolerance to high temperature (night/day thermoperiod of 25°C/35°C) during germination. Seeds from all maternal saline conditions germinate better in the 12 h photoperiod (12 h light/12 h dark) than in the dark (24 h dark); however, seeds produced from low and moderate maternal saline conditions (300 and 600 mM NaCl) show a higher germination in the dark than those from control and high maternal saline conditions (0 and 900 mM NaCl). In general, maternal salinity is found to improve yield, size and stress tolerance of S. fruticosa seeds.
Background and aims:
Pyroloids, forest sub-shrubs of the Ericaceae family, are an important model for their mixotrophic nutrition, which mixes carbon from photosynthesis and from their mycorrhizal fungi. They have medical uses but are difficult to cultivate ex situ; in particular, their dust seeds contain undifferentiated, few-celled embryos, whose germination is normally fully supported by fungal partners. Their germination and early ontogenesis thus remain elusive.
Methods:
An optimized in vitro cultivation system of five representatives from the subfamily Pyroloideae was developed to study the strength of seed dormancy and the effect of different media and conditions (including light, gibberellins and soluble saccharides) on germination. The obtained plants were analysed for morphological, anatomical and histochemical development.
Key results:
Thanks to this novel cultivation method, which breaks dormancy and achieved up to 100 % germination, leafy shoots were obtained in vitro for representatives of all pyroloid genera (Moneses, Orthilia, Pyrola and Chimaphila). In all cases, the first post-germination stage is an undifferentiated structure, from which a root meristem later emerges, well before formation of an adventive shoot.
Conclusions:
This cultivation method can be used for further research or for ex situ conservation of pyroloid species. After strong seed dormancy is broken, the tiny globular embryo of pyroloids germinates into an intermediary zone, which is functionally convergent with the protocorm of other plants with dust seeds such as orchids. Like the orchid protocorm, this intermediary zone produces a single meristem: however, unlike orchids, which produce a shoot meristem, pyroloids first generate a root meristem.
In his classic work on seeds published in 1946, Martin described the broad embryo as being wider than tall and listed it as occurring in four monocot and two dicot families and in genera of Cyperaceae and Commelinaceae. However, a preliminary survey of his “broad embryo” revealed a diversity of embryo shapes and structures. Our hypothesis that Martin defined a broad embryo solely on its outline/silhouette was supported by results of a detailed review of embryo and seed germination morphological characteristics of each family and genus he listed. We also included Piperaceae and Hydatellaceae since their embryos closely resemble those in the Saururaceae and Eriocaulaceae/Maycaceae/Xyridaceae, respectively. The various taxa can be subdivided into categories based on (1) presence or absence of organs in embryos of freshly-matured seeds, (2) undifferentiated embryo differentiates organs inside the seed vs. outside the seed and (3) food is stored in starchy endosperm vs. scant endosperm and copious starchy perisperm. The embryo in seeds of Eriocaulaceae/Maycaceae/Xyridaceae, other Poales with undifferentiated embryos and Hydatellaceae is wider than tall. This group of taxa has a lens- or bell-shaped undifferentiated embryo, leaves and roots are differentiated after the embryo is pushed/carried outside the seed and copious starchy endosperm is present, except in Hydatellaceae, which has starchy perisperm; this is the true “broad embryo”. The embryo in seeds of Saururaceae and Piperaceae is rudimentary (or pre-rudimentary) as described by Martin, that in Juncaceae, Cyperaceae and Commelinaceae a variation of the capitate embryo and the cup-like embryo in Nymphaeaceae and Cabomaceae is not known in other plant families and is therefore designated as the “cupulate embryo.”
Seed macro and micro morphological characters of the 18 taxa belonging to the family Acanthaceae have been examined by using light and scanning electron microscopy. The family Acanthaceae is represented by 2 sub families viz., Acanthoideae and Avicennioideae. A remarkable variation has been observed in seed size, shape, colour and surface at various taxonomic levels. Seed morphological data was also analyzed numerically by clustering to trace out the phylogenetic relationship and the data was found useful as an additional tool to strengthen the recognition of taxa within the family Acanthaceae from Pakistan.
Physical dormancy (PY) occurs in at least 18 angiosperm plant families and is caused by water-impermeable palisade cells in seed (or fruit) coats. Breaking of PY involves disruption or dislodgement of water-gap structures causing the seeds/fruits to become water permeable (non-dormant). The water-gap region is a morphologically distinct area of the seed or fruit coat that forms a water-gap complex. The location, anatomy, morphology and origin of water-gaps can differ between and even within families and genera. Water-gap structures sense environmental conditions that allow seeds with PY to become permeable just prior to the commencement of conditions favourable for germination and plant establishment. There are three basic water-gap morpho-anatomies characterized by the way the water-gap opens: Type-I, Type-II and Type-III. In Type-I water-gaps, specific kinds of cells pull apart to form a surface opening, while in Type-II a portion of the surface structure is pulled away from adjacent cells, opening the water-gap. Type-III is the least common type and has a circular, plug-like structure that is dislodged, whereby water entry occurs. In addition, water-gap complexes are either simple or compound, depending on whether only a single primary water-gap structure is involved in dormancy release or an additional secondary water-gap structure opens, permitting water entry.
Monotropa uniflora is an achlorophyllous angiosperm consisting of a mycorrhizae-dependent root system that produces floriferous, aerial shoots. Each of the numerous, minute ovules is anatropous, unitegmic, and contains a Polygonum type female gametophyte. Following double fertilization, a lipid-rich, cellular endosperm develops in association with both chalazal and micropylar haustoria. The vacuolate zygote elongates prior to a cytoplasmically unequal division resulting in a small terminal cell subtended by a larger, vacuolate basal cell. The basal cell eventually degenerates, isolating the terminal cell which is completely surrounded by endosperm. The terminal cell undergoes a cytoplasmically equal transverse division resulting in a two-celled embryo embedded in endosperm. In final stages of seed maturation, lipids decrease and reserve proteins increase in the cytoplasm of both the endosperm and embryo. The morphological reduction of the mature embryo may be associated with a specialized mode of nutrition.
Within the Monotropaceae. Monotropa hypopitys L. has the widest geographical distribution with sporophytes characterized as achlorophyllous, mycotrophic, and morphologically reduced. General and histochemical observations at the light microscope level concerning the postpollination changes in the numerous anatropous, unitegmic ovules reveal a precise embryogeny and endosperm development. Following double fertilization, the primary endosperm cell produces a lipid-rich cellular endosperm situated between a micropylar and a chalazal haustorium. A cytoplasmically unequal division of the elongated zygote initiates proembryo formation. The degeneration of the basal cell of the proembryo results in an isolated terminal cell that undergoes a cytoplasmically equal, transverse division establishing a two-celled embryo embedded in endosperm. Prior to final seed maturation, proteins replace the lipids as the dominant cytoplasmic reserve material. In contrast with earlier studies that depicted the mature embryo as variable in structure, here the embryo is shown to be consistently uniform within and between those populations sampled from North America and Europe.
Maheshwari, Satish C., and R. N. Kapil. (U. Delhi, Delhi, India.) Morphological and embryological studies on the Lemnaceae. II. The endosperm and embryo of Lemna paucicostata. Amer. Jour. Bot. 50(9): 907–914. Illus. 1963.—The first division of the primary endosperm nucleus is followed by wall formation. The second division is also transverse so that a longitudinal row of 4 cells is formed. The next 2 divisions are vertical and result in a 16-celled endosperm arranged in 4 tiers of 4 cells each. The development is, therefore, Cellular (even in L. minor) from the beginning and not Helobial, as reported earlier. The embryogeny conforms to the Asterad type. The radicle is absent in the mature embryo. Comparative studies of the structure of the endosperm and embryo furnish strong evidence in favor of a relationship of the Lemnaceae with the Araceae rather than with the Helobiales.
Mature seeds of Monotropa uniflora L., an achlorophyllous mycotrophic perennial, underwent imbibition and were processed for study using modern histological and histochemical techniques. The seeds ranged from 0.6-0.8 mm in length and 0.12-0.15 mm in width and exhibited integumentary winglike structures at either end. As in other members of the Ericaceae, seeds are unitegmic, tenuinucellate, albuminous, and form both micropylar and chalazal endosperm haustoria. A two-celled reduced embryo was observed in all seeds, except one where the embryo was three-celled. Protein granules in the thick walled endosperm were found to contain an aniline blue-fluorescent material that may be a calloselike carbohydrate. The limited amount of seed food reserves and the retardation of embryo differentiation may reflect specialized germination requirements.
Seed and pollen morphology were studied by light microscopy and scanning electron microscopy in 39 North and Central American species of Houstonia (including Hedyotis, but excluding Oldenlandia). Chromosome counts were obtained for eight taxa, of which five lacked previous chromosome data. A chromosome number of n = 17 for Houstonia gracilis is a new base number for the genus. Seed external morphology in the genus is very diverse, including variation in compression, margins, testa surfaces, and elaboration of ventral cavities or depressions and hilar ridges or their absence. Three types of pollen apertures are recognized: colporate with type A os, colpororate, and colporate with type B os, the last the most advanced type, occurring in H. caerulea and related species. The 39 species are arranged in twelve groups, based on correlation of seed, pollen, and chromosome data. Geographic distribution provides supplementary evidence for the distinctness and integrity of the six principal groups each composed of 2–9 species. Five of the six minor groups each with one species need chromosome data to facilitate future taxonomic decisions. Chromosome numbers of x = 6, 7, 8, 9, 10, 11, 13, and 17 are now known in this genus, and phylogenetic implications of the combined data are discussed.
The Carpathian flora occurs not only in the Carpathian Mountains, but also in large lowlands extending towards the south, north and east and involves introduced and invading flora of more than 7,500 species. Since the morphological characteristics of the seeds are usually constant they are very important for determination of systematic units. The present atlas of seeds with nearly 4,800 seed illustrations is supplemented with detailed seed descriptions, brief plant descriptions, locality and the native source of plants.
This publication is unique, both in its extent – with so many plant seeds from such a wide-ranging region - and in the form of its presentation – with such detailed descriptions.
Mycorrhizal fungi colonize orchid seeds and induce germination. This so-called symbiotic germination is a critical developmental process in the lifecycle of all orchid species. However, the molecular changes that occur during orchid seed symbiotic germination remains largely unknown. To better understand the molecular mechanism of orchid seed germination, we performed a comparative transcriptomic and proteomic analysis of the Chinese traditional medicinal orchid Dendrobium officinale for exploring change in protein expression at the different developmental stages during asymbiotic and symbiotic germination and identifing the key proteins that regulate the symbiotic germination of orchid seeds. Among 2256 identified plant proteins, 308 were differentially expressed across three developmental stages during asymbiotic and symbiotic germination and 229 were differentially expressed during symbiotic germination compared to asymbiotic development. Of these, 32 proteins were co-upregulated at both the proteomic and transcriptomic levels during symbiotic germination compared to asymbiotic germination. Our results suggest that symbiotic germination of D. officinale seeds shares a common signaling pathway with asymbiotic germination during the early germination stage. However, compared to asymbiotic germination, fungal colonization of orchid seeds appears to induce higher and earlier expression of some key proteins involved in lipid and carbohydrate metabolism and thus improves the efficiency of utilization of stored substances present in the embryo. This study provides new insight into the molecular basis of orchid seed germination.
Background and Aims Mycoheterotrophy entails plants meeting all or a portion of their carbon (C) demands via symbiotic interactions with root-inhabiting mycorrhizal fungi. Ecophysiological traits of mycoheterotrophs, such as their C stable isotope abundances, strongly correlate with the degree of species' dependency on fungal C gains relative to C gains via photosynthesis. Less explored is the relationship between plant evolutionary history and mycoheterotrophic plant ecophysiology. We hypothesized that the C and nitrogen (N) stable isotope compositions, and N concentrations of fully and partially mycoheterotrophic species differentiate them from autotrophs, and that plant family identity would be an additional and significant explanatory factor for differences in these traits among species. We focused on mycoheterotrophic species that associate with ectomycorrhizal fungi from plant families Ericaceae and Orchidaceae. • Methods: Published and unpublished data were compiled on the N concentrations, C and N stable isotope abundances (<5¹³C and <5¹⁵N) of fully (n = 18) and partially (n = 22) mycoheterotrophic species from each plant family as well as corresponding autotrophic reference species (n = 156). These data were used to calculate siteindependent C and N stable isotope enrichment factors (e). Then we tested for differences in N concentration, C and N enrichment among plant families and trophic strategies. • Key Results We found that in addition to differentiating partially and fully mycoheterotrophic species from each other and from autotrophs, C and N stable isotope enrichment also differentiates plant species based on familial identity. Differences in N concentrations clustered at the plant family level rather than the degree of dependency on mycoheterotrophy. • Conclusions We posit that differences in stable isotope composition and N concentrations are related to plant family-specific physiological interactions with fungi and their environments. © The Author 2016. Published by Oxford University Press on behalf of the Annals of Botany Company.
Numerical analysis based on seed morphological characters of 14 taxa belonging to the family Papaveraceae is carried out. Seed macro and micro morphological characters were found useful to strengthen the taxonomic decisions and trace out the phylogenetic relationship within the family Papaveraceae.
An update of the Angiosperm Phylogeny Group (APG) classification of the orders and families of angiosperms is presented. Several new orders are recognized: Boraginales, Dilleniales, Icacinales, Metteniusiales and Vahliales. This brings the total number of orders and families recognized in the APG system to 64 and 416, respectively. We propose two additional informal major clades, superrosids and superasterids, that each comprise the additional orders that are included in the larger clades dominated by the rosids and asterids. Families that made up potentially monofamilial orders, Dasypogonaceae and Sabiaceae, are instead referred to Arecales and Proteales, respectively. Two parasitic families formerly of uncertain positions are now placed: Cynomoriaceae in Saxifragales and Apodanthaceae in Cucurbitales. Although there is evidence that some families recognized in APG III are not monophyletic, we make no changes in Dioscoreales and Santalales relative to APG III and leave some genera in Lamiales unplaced (e.g. Peltanthera). These changes in familial circumscription and recognition have all resulted from new results published since APG III, except for some changes simply due to nomenclatural issues, which include substituting Asphodelaceae for Xanthorrhoeaceae (Asparagales) and Francoaceae for Melianthaceae (Geraniales); however, in Francoaceae we also include Bersamaceae, Ledocarpaceae, Rhynchothecaceae and Vivianiaceae. Other changes to family limits are not drastic or numerous and are mostly focused on some members of the lamiids, especially the former Icacinaceae that have long been problematic with several genera moved to the formerly monogeneric Metteniusaceae, but minor changes in circumscription include Aristolochiaceae (now including Lactoridaceae and Hydnoraceae; Aristolochiales), Maundiaceae (removed from Juncaginaceae; Alismatales), Restionaceae (now re-including Anarthriaceae and Centrolepidaceae; Poales), Buxaceae (now including Haptanthaceae; Buxales), Peraceae (split from Euphorbiaceae; Malpighiales), recognition of Petenaeaceae (Huerteales), Kewaceae, Limeaceae, Macarthuriaceae and Microteaceae (all Caryophyllales), Petiveriaceae split from Phytolaccaceae (Caryophyllales), changes to the generic composition of Ixonanthaceae and Irvingiaceae (with transfer of Allantospermum from the former to the latter; Malpighiales), transfer of Pakaraimaea (formerly Dipterocarpaceae) to Cistaceae (Malvales), transfer of Borthwickia, Forchhammeria, Stixis and Tirania (formerly all Capparaceae) to Resedaceae (Brassicales), Nyssaceae split from Cornaceae (Cornales), Pteleocarpa moved to Gelsemiaceae (Gentianales), changes to the generic composition of Gesneriaceae (Sanango moved from Loganiaceae) and Orobanchaceae (now including Lindenbergiaceae and Rehmanniaceae) and recognition of Mazaceae distinct from Phrymaceae (all Lamiales).