Systematic anatomy of Oceanopapaver, a monotypic genus of the Gapparaceae from New Caledonia

Evidence from vegetative anatomy, reproductive morphology, and palynology does not support a relationship of Oceanopapaver with Cistaceae, Cruciferae, Flacourtiaceae, Papaveraceae, and Tiliaceae, but suggests placement of the genus in Capparaceae. The apparent occurrence of myrosin cells, among other features, effectively excludes all of the aforenoted families except Capparaceae and Cruciferae. However, multicellular non-glandular trichomes, bracteate inflorescences, sepals and petals each occasionally other than four per flower, presence of an androgynophore, numerous stamens, tricolporate and binucleate pollen, the unilocular mature ovary, the stipitate fruit, and the exotegmic seed in Oceanopapaver favour Capparaceae over Cruciferae. Floral histology and vasculature provide no clues about the relationships of Oceanopapaver. A few features are anomalous, most notably the presence of secretory canals and secretory cells in the genus versus their absence in Capparaceae and their rarity in Cruciferae, the trichomic floral nectary in the genus versus the massive, non-trichomic nectaries in these two families, and the straight embryo in the genus versus the more or less curved or folded embryo in the two families. The fleshy endosperm in Oceanopapaver has counterparts in a few Capparaceae, contrary to previous claims that endosperm is absent or scanty in this family. The report of stamen fascicle traces for Oceanopapaver is the first for Capparaceae, but these should be sought elsewhere in the family. Within Capparaceae the genus fits best in Capparoideae compared to Cleomoideae or the nine other very restrictive subfamilies variously proposed for Capparaceae. There is no justification for the monotypic segregate Oceanopapaveraceae. The phylogenetic and functional anatomy of vegetative and reproductive structures is discussed.     

Bordered pits in ray cells and axial parenchyma: the histology of conduction, storage, and strength in living wood cells

Bordered pits occur in walls of living ray cells of numerous species of woody dicotyledons. The occurrence of this feature has been minimally reported because the pits are relatively small and not easily observed in face view. Bordered pits are illustrated in sectional view with light microscopy and with scanning electron microscopy in face view for dicotyledonous and gnetalean woods. Bordered pits are more numerous and often have prominent borders on tangential walls of procumbent ray cells, but also occur on radial walls; they are approximately equally abundant on tangential and horizontal walls of upright cells, suggesting parallels to cell shape in flow pathway design. Axial parenchyma typically has secondary walls thinner than those of ray cells, but bordered pits or large simple pit areas occur on some cross walls of parenchyma strands. There is no apparent correlation between the phylogenetic position of species and the presence of borders in ray cells or axial parenchyma. Bordered pits represent a compromise between maximal mechanical strength and maximal conductive capability. High rates of flow of sugar solutions may occur if starch in ray cells or axial parenchyma is mobilized for sudden osmotic enhancement of the conductive stream or for rapid development of foliage, flowers, or fruits. Measurement of the secondary wall thickness of ray cells may offer simple inferential information about the role that rays play in the mechanical strength of woods. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 153 , 157–168.     

The Deuterator: software for the determination of backbone amide deuterium levels from H/D exchange MS data

Background  

The combination of mass spectrometry and solution phase amide hydrogen/deuterium exchange (H/D exchange) experiments is an effective method for characterizing protein dynamics, and protein-protein or protein-ligand interactions. Despite methodological advancements and improvements in instrumentation and automation, data analysis and display remains a tedious process. The factors that contribute to this bottleneck are the large number of data points produced in a typical experiment, each requiring manual curation and validation, and then calculation of the level of backbone amide exchange. Tools have become available that address some of these issues, but lack sufficient integration, functionality, and accessibility required to address the needs of the H/D exchange community. To date there is no software for the analysis of H/D exchange data that comprehensively addresses these issues.     

Successive cambia in Aizoaceae: products and process

The transverse and longitudinal sections of the stems and roots of 11 genera of Aizoaceae, representing a wide range of growth forms from hard fibrous stems to fibre‐free roots, were studied using light microscopy and scanning electron microscopy. In most of the genera, fibres are the first xylary product of each vascular cambium, followed by vessels in a parenchyma background. Variations on this pattern help to prove that fibres are produced by vascular cambia, except in Ruschia and Stayneria, in which both the lateral meristem and the vascular cambia produce fibres. Cylinders of conjunctive tissue parenchyma that alternate with the vascular cylinders are produced by the lateral meristem. The concept that the lateral meristem gives rise to the vascular cambia and secondary cortex is supported by photographic evidence. Radial divisions occur in the origin of the lateral meristem, and then again as vascular cambia arise from the lateral meristem; these radial divisions account for storeying in fibres and conjunctive tissue. Raylessness characterizes all Aizoaceae studied, with the exception of Tetragonia, which also differs from the remaining genera by having vasicentric axial parenchyma, a scattering of vessels amongst fibres, and the presence of druses instead of raphides. Several vascular cambia are typically formed per year. Several vascular cambia are active simultaneously in a given stem or root. Roots have fewer fibres and more abundant conjunctive tissue parenchyma than stems. Successive cambia result in an ideal dispersion of vascular tissue with respect to water and photosynthate storage and retrieval capabilities of the parenchyma, and to liana stem plans. The distribution and relative abundance of fibres, vessels, secondary phloem, and conjunctive tissue parenchyma relate primarily to habit and are not a good source of systematic data, with the probable exception of Tetragonia. The general pattern of lateral meristem and vascular cambial ontogeny is the same as in other families of the core Caryophyllales, although the patterns of the tissues produced are diverse. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 153 , 141–155.     

Changes in thylakoid membrane thickness associated with the reorganization of photosystem II light harvesting complexes during photoprotective energy dissipation

Using freeze-fracture electron microscopy we have recently shown that non-photochemical quenching (NPQ), a mechanism of photoprotective energy dissipation in higher plant chloroplasts, involves a reorganization of the pigment-protein complexes within the stacked grana thylakoids.¹ Photosystem II light harvesting complexes (LHCII) are reorganized in response to the amplitude of the light driven transmembrane proton gradient (ΔpH) leading to their dissociation from photosystem II reaction centers and their aggregation within the membrane.¹ This reorganization of the PSII-LHCII macrostructure was found to be enhanced by the formation of zeaxanthin and was associated with changes in the mobility of the pigment-protein complexes therein.¹ We suspected that the structural changes we observed were linked to the ΔpH-induced changes in thylakoid membrane thickness that were first observed by Murikami and Packer.^2,3 Here using thin-section electron microscopy we show that the changes in thylakoid membrane thickness do not correlate with ΔpH per se but rather the amplitude of NPQ and is thus affected by the de-epoxidation of the LHCII bound xanthophyll violaxanthin to zeaxanthin. We thus suggest that the change in thylakoid membrane thickness occurring during NPQ reflects the conformational change within LHCII proteins brought about by their protonation and aggregation within the membrane.Key words: nonphotochemical quenching, photoprotection, LHCII, photosystem II, thylakoid membrane     

Challenges to understand plant responses to wind

Understanding plant response to wind is complicated as this factor entails not only mechanical stress, but also affects leaf microclimate. In a recent study, we found that plant responses to mechanical stress (MS) may be different and even in the opposite direction to those of wind. MS-treated Plantago major plants produced thinner more elongated leaves while those in wind did the opposite. The latter can be associated with the drying effect of wind as is further supported by data on petiole anatomy presented here. These results indicate that plant responses to wind will depend on the extent of water stress. It should also be recognized that the responses to wind may differ between different parts of a plant and between plant species. Physiological research on wind responses should thus focus on the signal sensing and transduction of both the mechanical and drought signals associated with wind, and consider both plant size and architecture.Key words: biomechanics, leaf anatomy, phenotypic plasticity, plant architecture, signal transduction thigmomorphogenesis, windWind is one of the most ubiquitous environmental stresses, and can strongly affect development, growth and reproductive yield in terrestrial plants.^1–3 In spite of more than two centuries of research,⁴ plant responses to wind and their underlying mechanisms remain poorly understood. This is because plant responses to mechanical movement themselves are complicated and also because wind entails not only mechanical effects, but also changes in leaf gas and heat exchange.^5–7 Much research on wind has focused primarily on its mechanical effect. Notably, several studies that determine plant responses to mechanical treatments such as flexing, implicitly extrapolate their results to wind effects.^8–10 Our recent study¹¹ showed that this may lead to errors as responses to wind and mechanical stimuli (in our case brushing) can be different and even in the opposite direction. In this paper, we first separately discuss plant responses to mechanical stimuli, and other wind-associated effects, and then discuss future challenges for the understanding of plant responses to wind.It is often believed that responses to mechanical stress (thigmomorphogenesis) entail the production of thicker and stronger plant structures that resist larger forces. This may be true for continuous unidirectional forces such as gravity, however for variable external forces (such as wind loading or periodic flooding) avoiding such mechanical stress by flexible and easily reconfigurable structures can be an alternative strategy.^12–14 How plants adapt or acclimate to such variable external forces depends on the intensity and frequency of stress and also on plant structures. Reduced height growth is the most common response to mechanical stimuli.^15,16 This is partly because such short stature increases the ability of plants to both resist forces (e.g., real-locating biomass for radial growth rather than elongation growth), and because small plants experience smaller drag forces (Fig. 1). Some plant species show a resistance strategy in response to mechanical stress by increasing stem thickness^1,10 and tissue strength.⁷ But other species show an avoidance strategy by a reduction in stem or petiole thickness and flexural rigidity in response to MS.^11,15–18 These different strategies might be associated with plant size and structure. Stems of larger plants such as trees and tall herbs are restricted in the ability to bend as they carry heavy loads^7,10,19 (Fig. 1). Conversely short plants are less restricted in this respect and may also be prone to trampling for which stress-avoidance would be the only viable strategy.^18,20 Systematic understanding of these various responses to mechanical stress remains to be achieved.Open in a separate windowFigure 1A graphical representation of how wind effects can be considered to entail both a drying and a mechanical effect. Adaptation or acclimation to the latter can be through a force resistance strategy or a force avoidance strategy, the benefit of which may depend on the size and architecture of plants as well as the location of a given structure within a plant.Wind often enhances water stress by reducing leaf boundary layers and reduces plant temperature by transpiration cooling. The latter effect may be minor,¹¹ but the former could significantly affect plant development. Anten et al. (2010) compared phenotypic traits and growth of Plantago major that was grown under mechanical stimuli by brushing (MS) and wind in the factorial design. Both MS and wind treatments reduced growth and influenced allocation in a similar manner. MS plants, however, had more slender petioles and narrower leaf blades while wind exposed plants exhibited the opposite response having shorter and relatively thicker petioles and more round-shaped leaf blades. MS plants appeared to exhibit stress avoidance strategy while such responses could be compensated or overridden by water stress in wind exposure.¹¹ A further analysis of leaf petiole anatomy (Fig. 2) supports this view. The vascular fraction in the petiole cross-section was increased by wind but not by MS, suggesting that higher water transport was required under wind. Our results suggest that drying effect of wind can at least to some extent override its mechanical effect.Open in a separate windowFigure 2Representative images of petiole cross-sections of Plantago major grown in 45 days in continuous wind and/or mechanical stimuli (A–D). Petiole cross-section area (E) and vascular bundle fraction in the cross-section of petiole (F). mean + SD (n = 12) are shown. Significance levels of ANOVA; ***p < 0.001, **p < 0.01, *p < 0.05, ns p > 0.05.Physiological knowledge on plant mechanoreception and signal transduction has been greatly increased during the last decades. Plants sense mechanical stimuli through membrane strain with stretch activated channels²¹ and/or through some linker molecules connecting the cell wall, plasma membrane and cytoskeleton.^4,22,23 This leads to a ubiquitous increase in intracellular Ca²⁺ concentration. The increased Ca²⁺ concentration is sensed by touch induced genes (TCHs),^24,25 which activates downstream transduction machineries including a range of signaling molecules and phytohormones, consequently altering physiological and developmental processes.²⁶ Extending this knowledge to understand plant phenotypic responses to wind however remains a challenge. As responses to wind have been found to differ among parts of a plant (e.g., terminal vs. basal stem) and also across species, physiological studies should be extended to the whole-plant as integrated system rather than focusing on specific tissue level. Furthermore to understand the general mechanism across species, it is required to study different species from different environmental conditions. Advances in bioinformatics, molecular and physiological research will facilitate cross-disciplinary studies to disentangle the complicated responses of plants to wind.     

Distinctive tracheid microstructure in stems of Victoria and Euryale (Nymphaeaceae)

Scanning electron microscopy (SEM) photographs of thick sections from liquid‐preserved stems of Victoria cruziana and Euryale ferox show accretions of coarse fibrils on pit membranes of tracheids. The first‐deposited fibrils are randomly orientated; on top of them (facing the tracheid lumina) are axially orientated coarse fibrils. The two systems are interconnected. Axially orientated fibrils were more extensively observed in Euryale than in Victoria and tips of fibrils in Euryale extend over the pit apertures onto secondary wall surfaces. Tracheid–parenchyma interfaces bear rudimentary coarse fibrils on the tracheid side. End walls of Victoria tracheids have highly porose pit membranes, thinner and less complex than those of the lateral intertracheid walls. The structures reported in Victoria and Euryale are consistent with those concurrently reported for stems of other Nymphaeaceae. Although also present in Cabombaceae, the coarse fibrils are otherwise not reported for stems of angiosperms and are not yet reported in roots of any species. Pit membrane remnants in perforation plates of various woody dicotyledons represent a nonhomologous phenomenon. The accretions of coarse fibrils in stem tracheids of Nymphaeaceae do not appear to enhance conduction, although they do contain porosities interconnecting tracheids. Removal of pit membrane remnants from perforation plates of primitive dicotyledon woods by hydrolysis does, on the contrary, suggest conduction enhancement. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 52–57.     

Evidence for effect of random genetic drift on G+C content after lateral transfer of fucose pathway genes to Escherichia coli K-12

The cps cluster of Escherichia coli K-12 comprises genes involved in synthesis of capsular polysaccharide colanic acid. Part of the E. coli K-12 cps region has been cloned and sequenced and compared to its Salmonella enterica LT2 counterpart. The cps genes from the two organisms are homologous; in the case of the LT2 genes, with G+C content of 0.61 and codons characteristic of high G+C species, it seems clear that they have been acquired relatively recently by lateral transfer from a high G+C species. The K-12 form of these cps genes is closely related to those of LT2 so must derive from the same high G+C species, but it appears to have transferred much earlier such that random genetic drift has brought P3 (the corrected G+C content of codon base 3) down from 0.77 to 0.64, more than halfway to the E. coli average of 0.57. We estimate, using an equation developed by Sueoka, that the lateral transfer to E. coli took place approximately 45 million years ago. This is the first report we are aware of demonstrating the expected adjustment of P3 after lateral transfer between species with different G+C content DNA.