Ultrastructure of stomatal development in early-divergent angiosperms reveals contrasting patterning and pre-patterning

Background and Aims

Angiosperm stomata consistently possess a pair of guard cells, but differ between taxa in the patterning and developmental origin of neighbour cells. Developmental studies of phylogenetically pivotal taxa are essential as comparative yardsticks for understanding the evolution of stomatal development.

Methods

We present a novel ultrastructural study of developing stomata in leaves of Amborella (Amborellales), Nymphaea and Cabomba (Nymphaeales), and Austrobaileya and Schisandra (Austrobaileyales), representing the three earliest-divergent lineages of extant angiosperms (the ANITA-grade).

Key Results

Alternative developmental pathways occur in early-divergent angiosperms, resulting partly from differences in pre-patterning and partly from the presence or absence of highly polarized (asymmetric) mitoses in the stomatal cell lineage. Amplifying divisions are absent from ANITA-grade taxa, indicating that ostensible similarities with the stomatal patterning of Arabidopsis are superficial. In Amborella, ‘squared’ pre-patterning occurs in intercostal regions, with groups of four protodermal cells typically arranged in a rectangle; most guard-mother cells are formed by asymmetric division of a precursor cell (the mesoperigenous condition) and are typically triangular or trapezoidal. In contrast, water-lily stomata are always perigenous (lacking asymmetric divisions). Austrobaileya has occasional ‘giant’ stomata.

Conclusions

Similar mature stomatal phenotypes can result from contrasting morphogenetic factors, although the results suggest that paracytic stomata are invariably the product of at least one asymmetric division. Loss of asymmetric divisions in stomatal development could be a significant factor in land plant evolution, with implications for the diversity of key structural and physiological pathways.     

Structure,ontogeny and taxonomic significance of trichomes and stomata in some Capparidaceae

The present work embodies epidermal structure, structure and ontogeny of stomata in five genera embracing sixteen species of the Capparidaceae namely Cleome (8 species) Capparis (5 species), Cadaba (1 species), Crataeva (1 species) and Maerua (1 species). The epidermal cells are polygonal, isodiametric or elongated arranged irregularly, with evenly or unevenly thickened, sinuous, straight or arched anticlinal walls. Two main types of trichomes: glandular (four types) and eglandular (five types) are noticed. The stomatal types include cyclocytic, triacytic, staurocytic, tetracytic, anomocytic, anisocytic, paracytic and with a single subsidiary cell. The ontogeny of stomata with a single subsidiary cell is perigenous or mesoperigenous, of paracytic mesoperigenous or mesogenous, of anisocytic is mesoperigenous or mesogenous, while that of the other types is perigenous. Abnormalities observed are: single guard cell; aborted guard cells; complete or incomplete division of guard cells; contiguous stomata; giant stomata and cytoplasmic connections. The present observations do not support the separation of Cleomaceae from the Capparidaceae.     

Variation in the structure and development of foliar stomata in the Euphorbiaceae

The structure and ontogeny of foliar stomata were studied in 50 species of 28 genera belonging to 17 tribes of the family Euphorbiaceae. The epidermal cells are either polygonal, trapezoidal, or variously elongated in different directions and diffusely arranged. The epidermal anticlinal walls are either straight, arched or sinuous. The architecture of cuticular striations varies with species. The mature stomata are paracytic (most common), anisocytic, anomocytic and diacytic. Occasionally a stoma may be tetracytic, cyclocytic or with a single subsidiary cell. The ontogeny of paracytic stomata is mesogenous dolabrate or trilabrate, mesoperigenous dolabrate; that of diacytic stomata is mesogenous dolabrate, whereas that of anisocytic stomata is mesogenous trilabrate; rarely an anisocytic stoma may be mesoperigenous. Hemiparacytic stomata are mesoperigenous unilabrate; tetracytic stomata are mesoperigenous dolabrate and anomocytic stomata perigenous. Abnormalities encountered include four types of contiguous stomata, stomata with a single or both guard cells aborted and persistent stomatal initials. Cytoplasmic connections between the guard cells of two adjacent stomata or the guard cell of a stoma and an adjacent epidermal/subsidiary cell, or both types occurring in a species, were noticed. The stomatal development, distribution, diversity and basic stomatal type with reference to systematics are discussed.     

Structure and Development of Stomata on the Vegetative and Floral Organs in Some Members of Caesalpiniaceae

The structure and development of stomata in 19 species of thefamily Caesalpiniaceae are described. The study is mostly confinedto the leaves, but observations have also been made on othervegetative and floral organs of some species Stomata may beparacytic, anisocytic, anomocytic, and with one subsidiary cell.Occasionally a stoma is diacytic, cyclocytic, or actinocytic.Different types occur individually or may be found side by sideeven on the same surface of an organ. The most prevalent typein all the genera is paracytic except in Caesalpima where itis anomocytic. The development of an anomocytic stoma is perigenous,but those with subsidiary cells are largely mesogenous; rarelyparacytic stomata are mesoperigenous. In spite of diversityof stomata, different types of stomata have similar patternsof development in different organs of the same plant. The presentinvestigation also indicates that the inconstancy of stomatain the family is due to (a) their diversity and (b) an increasein the number of subsidiary cells either by their division orby the neighbouring perigenes becoming subsidiary cell-like.     

Epidermal studies in some Indian cultivars of Bougainvilleas

Epidermal studies in fifteen Indian cultivars of Bougainvilleas are described. The epidermal cells are polygonal isodiametric, or elongated with thick straight arched or slightly sinuous walls. Parallel culticular striations are radiating from guard cells. The mature stomata are anomocytic, paracytic and with a single subsidiary cell. The abnormal types noticed are: single guard cells with or without pores, arrested development, variously oriented contiguous stomata, cytoplasmic connections between nearby stomata and epidermal or subsidiary cells, and persistent stomatal cells. The development of anomocytic stomata is perigenous while that of the other types is mesogenous. Fifteen cultivars of Bougainvilleas are separated on the basis of bract colour, stomatal frequency and index per unit area.     

Phylogeny of the cycads based on multiple single-copy nuclear genes: congruence of concatenated parsimony,likelihood and species tree inference methods

Background and aims

Despite a recent new classification, a stable phylogeny for the cycads has been elusive, particularly regarding resolution of Bowenia, Stangeria and Dioon. In this study, five single-copy nuclear genes (SCNGs) are applied to the phylogeny of the order Cycadales. The specific aim is to evaluate several gene tree–species tree reconciliation approaches for developing an accurate phylogeny of the order, to contrast them with concatenated parsimony analysis and to resolve the erstwhile problematic phylogenetic position of these three genera.

Methods

DNA sequences of five SCNGs were obtained for 20 cycad species representing all ten genera of Cycadales. These were analysed with parsimony, maximum likelihood (ML) and three Bayesian methods of gene tree–species tree reconciliation, using Cycas as the outgroup. A calibrated date estimation was developed with Bayesian methods, and biogeographic analysis was also conducted.

Key Results

Concatenated parsimony, ML and three species tree inference methods resolve exactly the same tree topology with high support at most nodes. Dioon and Bowenia are the first and second branches of Cycadales after Cycas, respectively, followed by an encephalartoid clade (Macrozamia–Lepidozamia–Encephalartos), which is sister to a zamioid clade, of which Ceratozamia is the first branch, and in which Stangeria is sister to Microcycas and Zamia.

Conclusions

A single, well-supported phylogenetic hypothesis of the generic relationships of the Cycadales is presented. However, massive extinction events inferred from the fossil record that eliminated broader ancestral distributions within Zamiaceae compromise accurate optimization of ancestral biogeographical areas for that hypothesis. While major lineages of Cycadales are ancient, crown ages of all modern genera are no older than 12 million years, supporting a recent hypothesis of mostly Miocene radiations. This phylogeny can contribute to an accurate infrafamilial classification of Zamiaceae.     

Phylogeny and Divergence Times of Gymnosperms Inferred from Single-Copy Nuclear Genes

Phylogenetic reconstruction is fundamental to study evolutionary biology and historical biogeography. However, there was not a molecular phylogeny of gymnosperms represented by extensive sampling at the genus level, and most published phylogenies of this group were constructed based on cytoplasmic DNA markers and/or the multi-copy nuclear ribosomal DNA. In this study, we use LFY and NLY, two single-copy nuclear genes that originated from an ancient gene duplication in the ancestor of seed plants, to reconstruct the phylogeny and estimate divergence times of gymnosperms based on a complete sampling of extant genera. The results indicate that the combined LFY and NLY coding sequences can resolve interfamilial relationships of gymnosperms and intergeneric relationships of most families. Moreover, the addition of intron sequences can improve the resolution in Podocarpaceae but not in cycads, although divergence times of the cycad genera are similar to or longer than those of the Podocarpaceae genera. Our study strongly supports cycads as the basal-most lineage of gymnosperms rather than sister to Ginkgoaceae, and a sister relationship between Podocarpaceae and Araucariaceae and between Cephalotaxaceae-Taxaceae and Cupressaceae. In addition, intergeneric relationships of some families that were controversial, and the relationships between Taxaceae and Cephalotaxaceae and between conifers and Gnetales are discussed based on the nuclear gene evidence. The molecular dating analysis suggests that drastic extinctions occurred in the early evolution of gymnosperms, and extant coniferous genera in the Northern Hemisphere are older than those in the Southern Hemisphere on average. This study provides an evolutionary framework for future studies on gymnosperms.     

Epidermal Structure and Stomatal Ontogeny in Some Eusporangiate Ferns

Cuticles, mature epidermis, and stomatal ontogeny in some speciesof the three genera of Ophioglossaceae and in Angiopteris evectawere studied. Development of stomata is perigenous in all Ophioglossaceaebut it is mesoperigenous (Piper type) in A. evecta.     

Chromosome patterns and nuclear phenomena in the cycad families Stangeriaceae and Zamiaceae

The chromosome karyotypes are described and scale diagrams prepared of 35 species representing 8 genera of the cycad families Stangeriaceae and Zamiaceae. The karyotype patterns, chromosome types and characteristics of the nucleolar organisers and heterochromatin are discussed in relation to their evolution in this ancient group of plants. A possible path of chromosome evolution is suggested by the concurrence in some genera of terminal heterochromatic knobs on chromosome arms and a single pair of telocentric homologues which in the remaining genera are replaced by complex partially heterochromatic nucleolar-organising chromosomes. — It is suggested that telocentric chromosomes may be of ancient origin in the cycads and that there may have been a progression from telocentric to mesocentric karyotypes. The paucity of genera today and the taxonomic isolation of the cycads from the remainder of the present-day flora renders impossible the corroboration of this theory by direct cytological comparisons with other groups.     

Real-time Imaging of Plant Cell Surface Dynamics with Variable-angle Epifluorescence Microscopy

A plant’s cell surface is its interface for perceiving environmental cues; it responds with cell biological changes such as membrane trafficking and cytoskeletal rearrangement. Real-time and high-resolution image analysis of such intracellular events will increase the understanding of plant cell biology at the molecular level. Variable angle epifluorescence microscopy (VAEM) is an emerging technique that provides high-quality, time-lapse images of fluorescently-labeled proteins on the plant cell surface. In this article, practical procedures are described for VAEM specimen preparation, adjustment of the VAEM optical system, movie capturing and image analysis. As an example of VAEM observation, representative results are presented on the dynamics of PATROL1. This is a protein essential for stomatal movement, thought to be involved in proton pump delivery to plasma membranes in the stomatal complex of Arabidopsis thaliana. VAEM real-time observation of guard cells and subsidiary cells in A. thaliana cotyledons showed that fluorescently-tagged PATROL1 appeared as dot-like structures on plasma membranes for several seconds and then disappeared. Kymograph analysis of VAEM movie data determined the time distribution of the presence (termed ‘residence time’) of the dot-like structures. The use of VAEM is discussed in the context of this example.     

Extant primitively segmented spiders have recently diversified from an ancient lineage

Living fossils are lineages that have retained plesiomorphic traits through long time periods. It is expected that such lineages have both originated and diversified long ago. Such expectations have recently been challenged in some textbook examples of living fossils, notably in extant cycads and coelacanths. Using a phylogenetic approach, we tested the patterns of the origin and diversification of liphistiid spiders, a clade of spiders considered to be living fossils due to their retention of arachnid plesiomorphies and their exclusive grouping in Mesothelae, an ancient clade sister to all modern spiders. Facilitated by original sampling throughout their Asian range, we here provide the phylogenetic framework necessary for reconstructing liphistiid biogeographic history. All phylogenetic analyses support the monophyly of Liphistiidae and of eight genera. As the fossil evidence supports a Carboniferous Euramerican origin of Mesothelae, our dating analyses postulate a long eastward over-land dispersal towards the Asian origin of Liphistiidae during the Palaeogene (39–58 Ma). Contrary to expectations, diversification within extant liphistiid genera is relatively recent, in the Neogene and Late Palaeogene (4–24 Ma). While no over-water dispersal events are needed to explain their evolutionary history, the history of liphistiid spiders has the potential to play prominently in vicariant biogeographic studies.     

Structure and Ontogeny of Stomata in Some Polemoniales

The ontogeny and structure of stomata in 22 genera and 51 speciesof the Polemoniales are described. Five main types of stomatanoticed are: anisocytic, anomocytic, diacytic, paracytic, andstomata with a single subsidiary cell. Three modes of stomataldevelopment: syndetocheilic or mesogenous, haplocheilic or perigenous,and meso-perigenous or syndeto-haplocheilic are observed. Abnormalitiesseen are: stomata with single guard cells, arrested developmentand contiguous stomata variously oriented. Contiguous stomataresult from adjacently placed meristemoids or readjustment duringmaturation. Stomata with a single guard cell are formed as aresult of degeneration of one of the guard cells before or afterpore formation. The stomatal apparatus varies in different organsof a plant in form, number, orientation and arrangement of thesubsidiary and also the surrounding cells. Three lines leadingto Polemoniales, Boraginales, and Solanales are distinet.     

Pseudodioon akyoli gen. et sp. nov., an extinct member of Cycadales from the Turkish Miocene

Fossil cycadalean leaves recorded from the Miocene plant assemblage of Soma, western Turkey, are described and assigned to an extinct genus and species, Pseudodioon akyoli. Leaf macromorphology suggests affinity with members of the Zamiaceae (subfam. Encephalartoideae), particularly with modern Dioon. Micromorphological features on the other hand indicate affinity with modern Cycas (Cycadaceae). Ordinary cells on the adaxial epidermis are isodiametric and are not differentiated into thick- and thin-walled cells. This is similar to Encephalartoideae-like fossils reported from the Cenozoic of the Northern Hemisphere, and even from the Mesozoic. Shared macromorphological traits of P. akyoli and other coeval Encephalartoideae-like fossil cycadalean leaves from Europe suggest that an extinct group of cycads inhabited southern Europe from the western part of Turkey, through Greece and France to Switzerland in the north during the Oligo-Miocene.     

Variation in climatic tolerance,but not stomatal traits,partially explains Pooideae grass species distributions

Background and AimsGrasses in subfamily Pooideae live in some of the world’s harshest terrestrial environments, from frigid boreal zones to the arid windswept steppe. It is hypothesized that the climate distribution of species within this group is driven by differences in climatic tolerance, and that tolerance can be partially explained by variation in stomatal traits.MethodsWe determined the aridity index (AI) and minimum temperature of the coldest month (MTCM) for 22 diverse Pooideae accessions and one outgroup, and used comparative methods to assess predicted relationships for climate traits versus fitness traits, stomatal diffusive conductance to water (g_w) and speed of stomatal closure following drought and/or cold.Key ResultsResults demonstrate that AI and MTCM predict variation in survival/regreening following drought/cold, and g_w under drought/cold is positively correlated with δ ¹³C-measured water use efficiency (WUE). However, the relationship between climate traits and fitness under drought/cold was not explained by g_w or speed of stomatal closure.ConclusionsThese findings suggest that Pooideae distributions are at least partly determined by tolerance to aridity and above-freezing cold, but that variation in tolerance is not uniformly explained by variation in stomatal traits.     

The oldest known chironomids of the tribe Tanytarsini (Diptera: Chironomidae) indicate plesiomorphic character states

Taxonomic studies on chironomids of the tribe Tanytarsini recorded in Eocene Baltic amber from the Rovno region have revealed two new species: Archistempellina perkovskyi and Stempellinella ivanovae. Both species display interesting characters supporting evolutionary trends in the tribe. A. perkovskyi nov. sp. combines plesiomorphic characters, thus consolidating the hypothesis that the genus Archistempellina is one of the basal lineages of the tribe Tanytarsini. The antennal flagellum composed of 13 discernible segments found in S. ivanovae nov. sp. is defined as a plesiomorphic character state opposite to a reduced number of flagellomeres in extant species; the nipple-like process on the apex of the gonostylus is recognised as a unique character in the Tanytarsini and a possible homologue of the horn-like tip of the gonostylus known from several extant species of the genus Stempellinella Brundin. A key to determination of all genera and species of the Tanytarsini recorded in the Eocene is presented. Notes on evolutionary trends in the tribe are also provided.     

Morphological development of Geissois pruinosa (Cunoniaceae) from seed to adult,and the expression of plesiomorphic characters in seedlings

Marked morphological changes occur during development from young seedlings to adults in Geissois pruinosa. At successive stages, leaves change from simple to trifoliolate and finally to 5-foliolate, palmately compound leaves, the margin of the blades changes from dentate to entire, the venation from craspedodromous to brochidodromous, and the stipules switch at about the 7th level from four free lateral ones per node to two fused intrapetiolar ones. Stems and leaves in young seedlings have sparse, erect hairs, but are glabrous in adults. Scattered and often incomplete information on other Cunoniaceae suggest that differences between seedlings and adults in other genera are generally less pronounced. Some seedling characters of G. pruinosa (including toothed leaflet margins and free lateral stipules) occur in the adult foliage of some of its close relatives (the genera Lamanonia and Pseudoweinmannia and Geissois in Australia) and are plesiomorphic within this clade.     

Epidermal micromorphology in Dioon: did volcanism constrain Dioon evolution?

The genus Dioon occupies an important phylogenetic position as sister to the other Zamiaceae. However, its epidermal morphology is still poorly known. We employed scanning and transmission electron microscopy, confocal microscopy and light microscopy to examine the epidermal and cuticular morphology of 12 of the 14 currently recognized species of Dioon, examining cultivated plants and herbarium specimens. Epidermal characters separate Dioon quite clearly from the other genera of the cycads. Within the genus, the major subgroups can be distinguished by their epidermal morphology. Some characters, such as the degree of stomatal protection, reflect ecological specializations in species within the subgroups. Several epidermal characters of the crown group Dioon seem to be absent in the Cenozoic fossils usually associated with the genus, which have been used as calibrations in many recent molecular dating analyses. The presence of similar characters in a Mesozoic fossil adapted to volcanic stress offers a new key in the interpretation of Dioon evolution. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179 , 236–254.     

Taxonomic and ecological implications of leaf cuticular morphology in Castanopsis, Castanea, and Chrysolepis

Leaves of 41 species of Castanopsis, six species of Castanea, and Chrysolepis chrysophyllum Hjelmq. were examined. In Castanopsis, all species possessed cyclocytic stomata with thickened subsidiary cells; thin-walled peltate trichomes are the most frequent type on the abaxial surface of the leaves of this genus. In Castanea, stomata are transitional between cyclocytic and anomocytic; thin-walled peltate trichomes were recorded for the first time on the abaxial surface of Castanea leaves. In Chrysolepis, cyclocytic stomata with non-thickened subsidiary cells and thick-walled peltate trichomes were observed. The thickened subsidiary cells support the placement of the “fissa-group” in Castanopsis. The results of this study support the idea that Castanopsis and Castanea are sister groups. Thick-walled peltate trichomes were only recorded in Chrysolepis, thus supporting its taxonomic separation from Castanopsis. The phylogenetic distribution of trichome types among genera of Fagaceae is summarized. The evolutionary trends of trichome types in Castanopsis are discussed, as are the implications of stomatal and trichome features on fossil identification and ecology.