Despite the relative simplicity of their modular growth, marine invertebrates such as arborescent gorgonian octocorals (Octocorallia: Cnidaria) generate complex colonial forms. Colony form in these taxa is a consequence of modular (polyp) replication, and if there is a tight integration among modular and supramodular traits (e.g. polyp aperture, inter-polyp spacing, branch thickness, internode and branch length), then changes at the module level may lead to changes in colony architecture. Alternatively, different groups of traits may evolve semi-independently (or conditionally independent). To examine the patterns of integration among morphological traits in Caribbean octocorals, we compared five morphological traits across 21 species, correcting for the effects of phylogenetic relationships among the taxa. Graphical modelling and phylogenetic independence contrasts among the five morphological characters indicate two groups of integrated traits based on whether they were polyp- or colony-level traits. Although all characters exhibited bivariate associations, multivariate analyses (partial correlation coefficients) showed the strongest integration among the colony-level characters (internode distance and branch length). It is a quantitative demonstration that branching characters within the octocorals studied are independent of characters of the polyps. Despite the universally recognized modularity of octocorals at the level of polyps, branching during colony development may represent an emergent level of integration and modularity.
During angiosperm evolution, innovations in vegetative and reproductive organs have resulted in tremendous morphological diversity, which has played a crucial role in the ecological success of flowering plants. Morindeae (Rubiaceae) display considerable diversity in growth form, inflorescence architecture, flower size, and fruit type. Lianescent habit, head inflorescence, small flower, and multiple fruit are the predominant states, but arborescent habit, non-headed inflorescence, large flower, and simple fruit states occur in various genera. This makes Morindeae an ideal model for exploring the evolutionary appearances and transitions between the states of these characters. We reconstructed ancestral states for these four traits using a Bayesian approach and combined nuclear/chloroplast data for 61 Morindeae species. The aim was to test three hypotheses: 1) self-supporting habit is generally ancestral in clades comprising both lianescent and arborescent species; 2) changes from lianescent to arborescent habit are uncommon due to “a high degree of specialization and developmental burden”; 3) head inflorescences and multiple fruits in Morindeae evolved from non-headed inflorescences and simple fruits, respectively. Lianescent habit, head inflorescence, large flower, and multiple fruit are inferred for Morindeae, making arborescent habit, non-headed inflorescence, small flower, and simple fruit derived within the tribe. The rate of change from lianescent to arborescent habit is much higher than the reverse change. Therefore, evolutionary changes between lianescent and arborescent forms can be reversible, and their frequency and trends vary between groups. Moreover, these changes are partly attributed to a scarcity of host trees for climbing plants in more open habitats. Changes from large to small flowers might have been driven by shifts to pollinators with progressively shorter proboscis, which are associated with shifts in breeding systems towards dioecy. A single origin of dioecy from hermaphroditism is supported. Finally, we report evolutionary changes from headed to non-headed inflorescences and multiple to simple fruits.
A new anatomically preserved fern, discovered from the basalmost Carboniferous of Australia, shows a unique combination of very primitive anatomical characters (solid centrarch cauline protostele) with the elaboration of an original model of the arborescent habit. This plant possessed a false trunk composed of a repetitive branching system of very small stems, which established it as the oldest tree-fern known to date. The potential of this primitive zygopterid fern to produce such an unusual growth form-without real equivalent among living plants-is related to the possession of two kinds of roots that have complementary functional roles: (i) large roots produced by stems with immediate positive geotropism, strongly adapted to mechanical support and water uptake from the soil; and (ii) small roots borne either on large roots or on petiole bases for absorbing humidity inside the false trunk.
Most species of the modern family Isoëtaceae (Quillworts) some other modern hydrophytes, use a metabolic pathway for carbon fixation that involves uptake of sedimentary carbon and enrichment of CO2 in internal gas spaces as a carbon-concentrating mechanism. This metabolism, which is related to ‘aquatic CAM’, is characterized by morphological, physiological and biochemical adaptations for decreasing photorespirative loss, aerating roots and maintaining high growth rates in anoxic, oligotrophic, stressed environments. Some of the closest relatives of the Isoëtaceae were the ‘arborescent lycopsids’, which were among the dominant taxa in the coal swamps found in lowland ecosystems during the Carboniferous and Permian periods (approx. 300 Ma). Morphological, ecological and geochemical evidence supports the hypothesis that the arborescent lycopsids had an unusual metabolism similar to that of modern Isoëtaceae and processed a biogeochemically significant proportion of organically fixed carbon over a period of about 100 million years in the late Palaeozoic. The temporal coincidence between the dominance of plants with this metabolism and an anomalous global atmosphere (high O2; low CO2) supports the idea that biosphere feedbacks are important in regulating global climatic homeostasis. The potential influence of this metabolism on the global carbon cycle and its specific adaptive function suggest that it should perhaps be considered a fourth major photosynthetic pathway.
aerenchyma; aquatic CAM; arborescent lycopsids; metabolic pathways; parichnos
The arborescent architecture of mammalian conductive airways results from the repeated branching of lung endoderm into surrounding mesoderm. Subsequent lung’s striking geometrical features have long raised the question of developmental mechanisms involved in morphogenesis. Many molecular actors have been identified, and several studies demonstrated the central role of Fgf10 and Shh in growth and branching. However, the actual branching mechanism and the way branching events are organized at the organ scale to achieve a self-avoiding tree remain to be understood through a model compatible with evidenced signaling. In this paper we show that the mere diffusion of FGF10 from distal mesenchyme involves differential epithelial proliferation that spontaneously leads to branching. Modeling FGF10 diffusion from sub-mesothelial mesenchyme where Fgf10 is known to be expressed and computing epithelial and mesenchymal growth in a coupled manner, we found that the resulting laplacian dynamics precisely accounts for the patterning of FGF10-induced genes, and that it spontaneously involves differential proliferation leading to a self-avoiding and space-filling tree, through mechanisms that we detail. The tree’s fine morphological features depend on the epithelial growth response to FGF10, underlain by the lung’s complex regulatory network. Notably, our results suggest that no branching information has to be encoded and that no master routine is required to organize branching events at the organ scale. Despite its simplicity, this model identifies key mechanisms of lung development, from branching to organ-scale organization, and could prove relevant to the development of other branched organs relying on similar pathways.
Diel (24 h) leaf growth patterns were differently affected by temperature variations and the circadian clock in several plant species. In the monocotyledon Zea mays, leaf elongation rate closely followed changes in temperature. In the dicotyledons Nicotiana tabacum, Ricinus communis, and Flaveria bidentis, the effect of temperature regimes was less obvious and leaf growth exhibited a clear circadian oscillation.These differences were related neither to primary metabolism nor to altered carbohydrate availability for growth. The effect of endogenous rhythms on leaf growth was analysed under continuous light in Arabidopsis thaliana, Ricinus communis, Zea mays, and Oryza sativa. No rythmic growth was observed under continuous light in the two monocotyledons, while growth rhythmicity persisted in the two dicotyledons. Based on model simulations it is concluded that diel leaf growth patterns in mono- and dicotyledons result from the additive effects of both circadian-clock-controlled processes and responses to environmental changes such as temperature and evaporative demand. Apparently very distinct diel leaf growth behaviour of monocotyledons and dicotyledons can thus be explained by the different degrees to which diel temperature variations affect leaf growth in the two groups of species which, in turn, depends on the extent of the leaf growth control by internal clocks.
Circadian clock; elongation; expansion; image analysis; photosynthesis; starch; sucrose
The holoparasitic plant genus Cuscuta comprises species with photosynthetic capacity and functional chloroplasts as well as achlorophyllous and intermediate forms with restricted photosynthetic activity and degenerated chloroplasts. Previous data indicated significant differences with respect to the plastid genome coding capacity in different Cuscuta species that could correlate with their photosynthetic activity. In order to shed light on the molecular changes accompanying the parasitic lifestyle, we sequenced the plastid chromosomes of the two species Cuscuta reflexa and Cuscuta gronovii. Both species are capable of performing photosynthesis, albeit with varying efficiencies. Together with the plastid genome of Epifagus virginiana, an achlorophyllous parasitic plant whose plastid genome has been sequenced, these species represent a series of progression towards total dependency on the host plant, ranging from reduced levels of photosynthesis in C. reflexa to a restricted photosynthetic activity and degenerated chloroplasts in C. gronovii to an achlorophyllous state in E. virginiana.
The newly sequenced plastid genomes of C. reflexa and C. gronovii reveal that the chromosome structures are generally very similar to that of non-parasitic plants, although a number of species-specific insertions, deletions (indels) and sequence inversions were identified. However, we observed a gradual adaptation of the plastid genome to the different degrees of parasitism. The changes are particularly evident in C. gronovii and include (a) the parallel losses of genes for the subunits of the plastid-encoded RNA polymerase and the corresponding promoters from the plastid genome, (b) the first documented loss of the gene for a putative splicing factor, MatK, from the plastid genome and (c) a significant reduction of RNA editing.
Overall, the comparative genomic analysis of plastid DNA from parasitic plants indicates a bias towards a simplification of the plastid gene expression machinery as a consequence of an increasing dependency on the host plant. A tentative assignment of the successive events in the adaptation of the plastid genomes to parasitism can be inferred from the current data set. This includes (1) a loss of non-coding regions in photosynthetic Cuscuta species that has resulted in a condensation of the plastid genome, (2) the simplification of plastid gene expression in species with largely impaired photosynthetic capacity and (3) the deletion of a significant part of the genetic information, including the information for the photosynthetic apparatus, in non-photosynthetic parasitic plants.
During embryogenesis motor axons navigate to their target muscles, where individual motor axons develop complex branch morphologies. The mechanisms that control axonal branching morphogenesis have been studied intensively, yet it still remains unclear when branches begin to form or how branch locations are determined. Live cell imaging of individual zebrafish motor axons reveals that the first axonal branches are generated at the ventral extent of the myotome via bifurcation of the growth cone. Subsequent branches are generated by collateral branching restricted to their synaptic target field along the distal portion of the axon. This precisely timed and spatially restricted branching process is disrupted in turnout mutants we identified in a forward genetic screen. Molecular genetic mapping positioned the turnout mutation within a 300 kb region encompassing eight annotated genes, however sequence analysis of all eight open reading frames failed to unambiguously identify the turnout mutation. Chimeric analysis and single cell labeling reveal that turnout function is required cell non-autonomously for intraspinal motor axon guidance and peripheral branch formation. turnout mutant motor axons form the first branch on time via growth cone bifurcation, but unlike wild-type they form collateral branches precociously, when the growth cone is still navigating towards the ventral myotome. These precocious collateral branches emerge along the proximal region of the axon shaft typically devoid of branches, and they develop into stable, permanent branches. Furthermore, we find that null mutants of the guidance receptor plexin A3 display identical motor axon branching defects, and time lapse analysis reveals that precocious branch formation in turnout and plexin A3 mutants is due to increased stability of otherwise short-lived axonal protrusions. Thus, plexin A3 dependent intrinsic and turnout dependent extrinsic mechanisms suppress collateral branch morphogenesis by destabilizing membrane protrusions before the growth cone completes navigation into the synaptic target field.
Some Escherichia coli strains with impaired cell division form branched cells at high frequencies during certain growth conditions. Here, we show that neither FtsI nor FtsZ activity is required for the development of branches. Buds did not form at specific positions along the cell surface during high-branching conditions. Antibiotics affecting cell wall synthesis had a positive effect on branch formation in the case of ampicillin, cephalexin, and penicillin G, whereas mecillinam and d-cycloserine had no substantial effect. Altering the cell morphology by nutritional shifts showed that changes in morphology preceded branching, indicating that the cell’s physiological state rather than specific medium components induced branching. Finally, there was no increased probability for bud formation in the daughters of a cell with a bud or branch, showing that bud formation is a random event. We suggest that branch formation is caused by abnormalities in cell wall elongation rather than by aberrant cell division events.
Background and Aims
Decaisnea insignis, known as ‘dead man's fingers’ (Lardizabalaceae), is widely distributed in China and the Himalayan foothill countries. This economically important plant, which is the only species in the genus, has not been the subject of any embryological studies aside from one brief, older paper that lacks micrographs. Data on Decaisnea are also important because its systematic position has been unstable since the genus was established in 1855. Therefore, the objectives of this study were: (a) to use modern microscopy to document early reproductive anatomical development in Decaisnea; and (b) to compare qualitatively these early embryological characters with allied taxa in a systematic context.
Decaisnea insignis floral buds and inflorescences were regularly collected from Shaanxi Province, China and prepared for light microscopy. The embryological characters studied were qualitatively compared with those of allied taxa via a thorough examination of the existing literature.
Early reproductive anatomy in Decaisnea was documented and novel revelations made. It was discovered that the pollen is shed when three-celled (not two-celled, as previously reported), and that endosperm formation is nuclear (not cellular or helobial, as previously reported). These two newly revealed embryological characters are not found in any other members of Lardizabalaceae. Furthermore, neither are persistent antipodal cells, which we confirmed to be present in Decaisnea.
Decaisnea and other Lardizabalaceae characteristically have tetrasporangiate anthers, a secretory tapetum, simultaneous microsporocyte cytokinesis, primarily bitegmic, crassinucellate ovules, and a Polygonum type embryo sac. However, in the family, persistent antipodals, nuclear endosperm, and pollen shed at the three-celled stage are only found in Decaisnea. These embryological data prompted the suggestion that Decaisnea needs elevation above the level of genus.
Decaisnea insignis; embryology; endosperm; Lardizabalaceae; microscopy; pollen; reproductive anatomy; systematics
Background and Aims
Forest tree saplings that grow in the understorey undergo frequent changes in their light environment to which they must adapt to ensure their survival and growth. Crown architecture, which plays a critical role in light capture and mechanical stability, is a major component of sapling adaptation to canopy disturbance. Shade-adapted saplings typically have plagiotropic stems and branches. After canopy opening, they need to develop more erect shoots in order to exploit the new light conditions. The objective of this study was to test whether changes in sapling stem inclination occur after canopy opening, and to analyse the morphological changes associated with stem reorientation.
A 4-year canopy-opening field experiment with naturally regenerated Fagus sylvatica and Acer pseudoplatanus saplings was conducted. The appearance of new stem axes, stem basal diameter and inclination along the stem were recorded every year after canopy opening.
Both species showed considerable stem reorientation resulting primarily from uprighting (more erect) shoot movements in Fagus, and from uprighting movements, shoot elongation and formation of relay shoots in Acer. In both species, the magnitude of shoot uprighting movements was primarily related to initial stem inclination. Both the basal part and the apical part of the stem contributed to uprighting movements. Stem movements did not appear to be limited by stem size or by stem growth.
Stem uprighting movements in shade-adapted Fagus and Acer saplings following canopy disturbance were considerable and rapid, suggesting that stem reorientation processes play a significant role in the growth strategy of the species.
Advance regeneration; canopy gap; biomechanics; gravitropism; shade tolerance; Fagus sylvatica; Acer pseudoplatanus
Mitochondria have the capacity to integrate environmental signals and, in animals with active stem cell populations, trigger responses in terms of growth and growth form. Colonial hydroids, which consist of feeding polyps connected by tube-like stolons, were treated with avicins, triterpenoid electrophiles whose anti-cancer properties in human cells are mediated in part by mitochondria. In treated hydroids, both oxygen uptake and mitochondrial reactive oxygen species were diminished relative to controls, similar to that observed in human cells exposed to avicins. While untreated colonies exhibit more stolon branches and connections in the centre of the colony than at the periphery, treated colonies exhibit the opposite: fewer stolon branches in the centre of the colony than at the periphery. The resulting growth form suggests an inversion of the normal pattern of colony development mediated by mitochondrial and redox-related perturbations. An as-yet-uncharacterized gradient within the colony may determine the ultimate phenotypic effect of avicin perturbation.
avicins; cancer; hydroids; Podocoryna; reactive oxygen species; redox state
Background and Aims
ADP-glucose pyrophosphorylase (AGPase) is a key enzyme of starch biosynthesis. In the green plant lineage, it is composed of two large (LSU) and two small (SSU) sub-units encoded by paralogous genes, as a consequence of several rounds of duplication. First, our aim was to detect specific patterns of molecular evolution following duplication events and the divergence between monocotyledons and dicotyledons. Secondly, we investigated coevolution between amino acids both within and between sub-units.
A phylogeny of each AGPase sub-unit was built using all gymnosperm and angiosperm sequences available in databases. Accelerated evolution along specific branches was tested using the ratio of the non-synonymous to the synonymous substitution rate. Coevolution between amino acids was investigated taking into account compensatory changes between co-substitutions.
We showed that SSU paralogues evolved under high functional constraints during angiosperm radiation, with a significant level of coevolution between amino acids that participate in SSU major functions. In contrast, in the LSU paralogues, we identified residues under positive selection (1) following the first LSU duplication that gave rise to two paralogues mainly expressed in angiosperm source and sink tissues, respectively; and (2) following the emergence of grass-specific paralogues expressed in the endosperm. Finally, we found coevolution between residues that belong to the interaction domains of both sub-units.
Our results support the view that coevolution among amino acid residues, especially those lying in the interaction domain of each sub-unit, played an important role in AGPase evolution. First, within SSU, coevolution allowed compensating mutations in a highly constrained context. Secondly, the LSU paralogues probably acquired tissue-specific expression and regulatory properties via the coevolution between sub-unit interacting domains. Finally, the pattern we observed during LSU evolution is consistent with repeated sub-functionalization under ‘Escape from Adaptive Conflict’, a model rarely illustrated in the literature.
Angiosperms; monocotyledons; dicotyledons; paralogue genes; molecular evolution; coevolution; neofunctionalization; subfunctionalization; starch synthesis; AGPase
Understanding external deciding factors in growth and morphology of reef corals is essential to elucidate the role of corals in marine ecosystems, and to explain their susceptibility to pollution and global climate change. Here, we extend on a previously presented model for simulating the growth and form of a branching coral and we compare the simulated morphologies to three-dimensional (3D) images of the coral species Madracis mirabilis. Simulation experiments and isotope analyses of M. mirabilis skeletons indicate that external gradients of dissolved inorganic carbon (DIC) determine the morphogenesis of branching, phototrophic corals. In the simulations we use a first principle model of accretive growth based on local interactions between the polyps. The only species-specific information in the model is the average size of a polyp. From flow tank and simulation studies it is known that a relatively large stagnant and diffusion dominated region develops within a branching colony. We have used this information by assuming in our model that growth is entirely driven by a diffusion-limited process, where DIC supply represents the limiting factor. With such model constraints it is possible to generate morphologies that are virtually indistinguishable from the 3D images of the actual colonies.
morphogenesis; scleractinian corals; diffusion-limited growth; morphological plasticity; computed tomography scanning; stable isotope analysis
The cell walls in plants are made up of just four basic building blocks: cellulose (the main structural fibre of the plant kingdom) hemicellulose, lignin and pectin. Although the microstructure of plant cell walls varies in different types of plants, broadly speaking, cellulose fibres reinforce a matrix of hemicellulose and either pectin or lignin. The cellular structure of plants varies too, from the largely honeycomb-like cells of wood to the closed-cell, liquid-filled foam-like parenchyma cells of apples and potatoes and to composites of these two cellular structures, as in arborescent palm stems. The arrangement of the four basic building blocks in plant cell walls and the variations in cellular structure give rise to a remarkably wide range of mechanical properties: Young's modulus varies from 0.3 MPa in parenchyma to 30 GPa in the densest palm, while the compressive strength varies from 0.3 MPa in parenchyma to over 300 MPa in dense palm. The moduli and compressive strength of plant materials span this entire range. This study reviews the composition and microstructure of the cell wall as well as the cellular structure in three plant materials (wood, parenchyma and arborescent palm stems) to explain the wide range in mechanical properties in plants as well as their remarkable mechanical efficiency.
plant materials; mechanics; wood; parenchyma; palm stems
Plant matrix metalloproteinases (MMP) are conserved proteolytic enzymes found in a wide range of monocotyledonous and dicotyledonous plant species. Acting on the plant extracellular matrix, they play crucial roles in many aspects of plant physiology including growth, development and the response to stresses such as pathogen attack.
We have identified the first tobacco MMP, designated NtMMP1, and have isolated the corresponding cDNA sequence from the tobacco suspension cell line BY-2. The overall domain structure of NtMMP1 is similar to known MMP sequences, although certain features suggest it may be constitutively active rather than dependent on proteolytic processing. The protein appears to be expressed in two forms with different molecular masses, both of which are enzymatically active as determined by casein zymography. Exchanging the catalytic domain of NtMMP1 with green fluorescent protein (GFP) facilitated subcellular localization by confocal laser scanning microscopy, showing the protein is normally inserted into the plasma membrane. The NtMMP1 gene is expressed constitutively at a low level but can be induced by exposure to bacterial pathogens.
Our biochemical analysis of NtMMP1 together with bioinformatic data on the primary sequence indicate that NtMMP1 is a constitutively-active protease. Given its induction in response to bacterial pathogens and its localization in the plasma membrane, we propose a role in pathogen defense at the cell periphery.
Background and Aims
Consistent abiotic factors can affect directional selection; cyclones are abiotic phenomena with near-discrete geographic limits. The current study investigates selective pressure of cyclones on plants at the species level, testing for possible natural selection.
New World Arecaceae (palms) are used as a model system, as plants with monopodial, unbranched arborescent form are most directly affected by the selective pressure of wind load. Living specimens of known provenance grown at a common site were affected by the same cyclone. Data on percentage mortality were compiled and analysed in biogeographic and phylogenetic contexts.
Palms of cyclone-prone provenance exhibited a much lower (one order of magnitude) range in cyclone tolerance, and significantly lower (P < 0·001) mean percentage mortality than collections from cyclone-free areas. Palms of cyclone-free provenance had much greater variation in tolerance, and significantly greater mean percentage mortality. A test for serial independence recovered no significant phylogenetic autocorrelation of percentage mortality.
Variation in cyclone tolerance in New World Arecaceae correlates with biogeography, and is not confounded with phylogeny. These results suggest natural selection of cyclone tolerance in cyclone-prone areas.
Abiotic selection; Arecaceae; biogeography; cyclone; hurricane; phylogenetic independence
A study has been made of the cells of the left colleterial gland of the cockroach, Periplaneta americana (L.), using the electron microscope, and the results compared with previous histological and histochemical studies. The colleterial gland consists of an arborescent bunch of long tubules composed mainly of the cells which secrete the structural protein of the egg case ("type 4 cells"). Other types of cells: chitinogenic cells and "type 2 and 3 cells" each with a different cytology are described. The type 4 cells, which form the structural protein, reveal a cytological pattern very similar to that described for mammalian cells in a state of active protein synthesis. There is an elaborate development of particle-studded membranes in the cytoplasm. Smaller, rounded agranular vesicles also occur. The free secretory surface of the secreting cells forms the "end-apparatus" of the light microscopists. The invaginated surface is cast into numerous long narrow processes usually radially arranged and directed into a funnel-like formation derived from the thin intima lining the lumen of the gland (Text-fig. 2). The secretion in the form of small balls may be seen in the cavity of the end-apparatus and sometimes in the narrow processes. The small chitinogenic cells, lying between the protein-forming cells and the thin intima which they secrete, have a different cytology perhaps related to the fact that they form a polysaccharide rather than a protein. There is a very poor development of the particle-studded membranes of the type found in protein-forming cells. The type 2 cells, supposed to form an oxidase, have an end-apparatus that is similar to, but more complex than, those of the type 4 cells and their cytoplasm is almost completely filled with mitochondria. There is some evidence that mitochondria play a part in forming the oxidase and pass into the tubules of the end-apparatus. Type 3 cells resemble both types 2 and 4 and are probably a transient intermediate form.
• Background and Aims Growth in trunk height in canopy openings is important for saplings. How saplings increase height growth in canopy openings may relate to crown architectural constraints. Responses of crown development to canopy openings in relation to trunk height growth were studied for saplings (0·2–2·5 m tall) of eight tropical submontane forest tree species in Indonesia. The results of this study were also compared with those of temperate trees in northern Japan.
• Methods The crown architecture differed among the eight tropical species, i.e. they had sparsely to highly developed branching structures. Crown allometry was compared among the eight species in each canopy condition (closed canopy or canopy openings), and between closed canopy and canopy openings within a species. A general linear regression model was used to analyse how each species increases height growth rate in canopy openings. Crown allometry and its plasticity were compared between tropical and temperate trees by a nested analysis of covariance.
• Key Results Tropical submontane trees had responses similar to cool-temperate trees, showing an increase in height in canopy openings, i.e. taller saplings of sparsely branched species increase height growth rates by increasing the sapling leaf area. Cool-temperate trees have a wider crown projection area and a smaller leaf area per crown projection area to avoid self-shading within a crown compared with tropical submontane trees. Plasticity of the crown projection area is greater in cool-temperate trees than in tropical submontane trees, probably because of the difference in leaf longevity.
• Conclusions This study concluded that interspecific variation in the responses of crown development to canopy openings in regard to increasing height related to the species' branching structure, and that different life-forms, such as evergreen and deciduous trees, had different crown allometry and plasticity.
Cool-temperate trees; crown allometry; crown architecture; height growth; Indonesia; saplings; plasticity; tropical trees
The function of vasodilator-stimulated phosphoprotein (VASP) in motility is analyzed using a biomimetic motility assay in which ActA-coated microspheres propel themselves in a medium containing actin, the Arp2/3 complex, and three regulatory proteins in the absence or presence of VASP. Propulsion is linked to cycles of filament barbed end attachment-branching-detachment-growth in which the ActA-activated Arp2/3 complex incorporates at the junctions of branched filaments. VASP increases the velocity of beads. VASP increases branch spacing of filaments in the actin tail, as it does in lamellipodia in living cells. The effect of VASP on branch spacing of Arp2/3-induced branched actin arrays is opposed to the effect of capping proteins. However, VASP does not compete with capping proteins for binding barbed ends of actin filaments. VASP enhances branched actin polymerization only when ActA is immobilized on beads or on Listeria. VASP increases the rate of dissociation of the branch junction from immobilized ActA, which is the rate-limiting step in the catalytic cycle of site-directed filament branching.
Arp2/3; filament branching; site-directed polymerization; VASP; ActA
In addition to experimental studies, computational models provide valuable information about colony development in scleractinian corals. Using our simulation model, we show how environmental factors such as nutrient distribution and light availability affect growth patterns of coral colonies. To compare the simulated coral growth forms with those of real coral colonies, we quantitatively compared our modelling results with coral colonies of the morphologically variable Caribbean coral genus Madracis. Madracis species encompass a relatively large morphological variation in colony morphology and hence represent a suitable genus to compare, for the first time, simulated and real coral growth forms in three dimensions using a quantitative approach. This quantitative analysis of three-dimensional growth forms is based on a number of morphometric parameters (such as branch thickness, branch spacing, etc.). Our results show that simulated coral morphologies share several morphological features with real coral colonies (M. mirabilis, M. decactis, M. formosa and M. carmabi). A significant correlation was found between branch thickness and branch spacing for both real and simulated growth forms. Our present model is able to partly capture the morphological variation in closely related and morphologically variable coral species of the genus Madracis.
corals; morphogenesis; morphology; simulation; CT scan; Madracis
Malagasy Dracaena (Ruscaceae) are divided into four species and 14 varieties, all of them showing a high level of morphological diversity and a putatively artefactual circumscription. In order to reveal relationships between those entangled entities, a span of Malagasy Dracaena were sampled and analyzed using cpDNA sequences and AFLP. The cpDNA analyses resolved three biogeographic clades that are mostly inconsistent with morphology, since similar phenotypes are found across the three clades. Bayesian inference clustering analyses based on the AFLP were not in accordance with the cpDNA analysis. This result might be explained by (1) a recent origin of the Malagasy species of Dracaena with an incomplete sorting of chloroplast lineages; (2) a high amount of hybridizations; (3) a complex migration pattern. Interestingly, when the AFLP are analyzed using the parsimony criterion, a trend towards a directional evolution of inflorescence types and ecological features was observed. This might be considered either as phenotypic plasticity and/or as the result of fast evolution in flower characters according to habitat preferences. Overall, our results point to the difficulty of defining evolutionarily significant units in Malagasy Dracaena, emphasizing the complex speciation processes taking place in tropical regions.
AFLP; Biogeography; cpDNA; Incomplete lineage sorting; Malagasy Dracaena; Phenotypic plasticity
The plant parasite Cuscuta reflexa induces various responses in compatible and incompatible host plants. The visual reactions of both types of host plants including obvious morphological changes require the recognition of Cuscuta ssp. A consequently initiated signaling cascade is triggered which leads to a tolerance of the infection or, in the case of some incompatible host plants, to resistance. Calcium (Ca2+) release is the major second messenger during signal transduction. Therefore, we have studied Ca2+ spiking in tomato and tobacco during infection with C. reflexa. In our recently published study1 Ca2+ signals were monitored as bioluminescence in aequorin-expressing tomato plants after the onset of C. reflexa infestation. Signals at the attachment sites were observed from 30 to 48 h after infection. In an assay with leaf disks of aequorin-expressing tomato which were treated with different C. reflexa plant extracts it turned out that the substance that induced Ca2+ release in the host plant was closely linked to the parasite's haustoria.
cuscut; odder; calcium signaling; plant parasitism
The association of pericytes (PCs) to newly formed blood vessels has been suggested to regulate endothelial cell (EC) proliferation, survival, migration, differentiation, and vascular branching. Here, we addressed these issues using PDGF-B– and PDGF receptor-β (PDGFR-β)–deficient mice as in vivo models of brain angiogenesis in the absence of PCs. Quantitative morphological analysis showed that these mutants have normal microvessel density, length, and number of branch points. However, absence of PCs correlates with endothelial hyperplasia, increased capillary diameter, abnormal EC shape and ultrastructure, changed cellular distribution of certain junctional proteins, and morphological signs of increased transendothelial permeability. Brain endothelial hyperplasia was observed already at embryonic day (E) 11.5 and persisted throughout development. From E 13.5, vascular endothelial growth factor-A (VEGF-A) and other genes responsive to metabolic stress became upregulated, suggesting that the abnormal microvessel architecture has systemic metabolic consequences. VEGF-A upregulation correlated temporally with the occurrence of vascular abnormalities in the placenta and dilation of the heart. Thus, although PC deficiency appears to have direct effects on EC number before E 13.5, the subsequent increased VEGF-A levels may further abrogate microvessel architecture, promote vascular permeability, and contribute to formation of the edematous phenotype observed in late gestation PDGF-B and PDGFR-β knock out embryos.
mice; angiogenesis; pericytes; platelet-derived growth factor B; vascular endothelial growth factor
Differentiation of long and short shoots is an important developmental trait in several species of the Rosaceae family. However, the physiological mechanisms controlling this differentiation are largely unknown. We have studied the role of gibberellin (GA) in regulation of shoot differentiation in strawberry (Fragaria × ananassa Duch.) cv. Korona. In strawberry, differentiation of axillary buds to runners (long shoot) or to crown branches (short shoot) is promoted by long-day and short-day conditions, respectively. Formation of crown branches is a prerequisite for satisfactory flowering because inflorescences are formed from the apical meristems of the crown.
We found that both prohexadione-calcium and short photoperiod inhibited runner initiation and consequently led to induction of crown branching. In both cases, this correlated with a similar decline in GA1 level. Exogenous GA3 completely reversed the effect of prohexadione-calcium in a long photoperiod, but was only marginally effective in short-day grown plants. However, transfer of GA3-treated plants from short days to long days restored the normal runner formation. This did not occur in plants that were not treated with GA3. We also studied GA signalling homeostasis and found that the expression levels of several GA biosynthetic, signalling and target genes were similarly affected by prohexadione-calcium and short photoperiod in runner tips and axillary buds, respectively.
GA is needed for runner initiation in strawberry, and the inhibition of GA biosynthesis leads to the formation of crown branches. Our findings of similar changes in GA levels and in GA signalling homeostasis after prohexadione-calcium and short-day treatments, and photoperiod-dependent responsiveness of the axillary buds to GA indicate that GA plays a role also in the photoperiod-regulated differentiation of axillary buds. We propose that tightly regulated GA activity may control induction of cell division in subapical tissues of axillary buds, being one of the signals determining bud fate.