Biophysical Examinations of the Bending Stability of Various Stele Types and the Upright Axes of Early “Vascular” Land Plants

Biophysical methods allow quantitative deductions as to the “bending effectivity” of various stele types and the contribution of different tissues to the stability of upright plant axes. Considering the first occurrence of the different stele types in geological history, a strong tendency towards a higher “bending effectivity” can be observed. It can be shown that Rhynia gwynne-vaughanii, Aglaophyton major (Rhynia major) and Asteroxylon mackiei as well as probably the vast majority of early “vascular” land plants were turgor systems, i.e. that the parenchyma (when fully turgescent) is by far the most important contributory factor towards the bending stability of the upright axes.     

The Biomechanics of Tree Fork Design

Two biomechanically different types of tree fork are described: the “compression fork” where the two jointed stems are pressed against each other at the contact face by the action of reaction wood, and the “tension fork” where the two connected stems are bent away from each other by gravity or wind action leading to tensile stresses in the connective zone. It is well known that trees permanently try to improve their own designs by adaptive growth in order to maintain a state of constant mechanical stress at the tree surface. In the case of these two different types of tree fork, adaptive growth also takes different ways in order to avoid high localized stress peaks which could lead to failure of the tree under wind loading. In this paper only the tension fork is assessed with respect to its shape optimization by computer simulation of adaptive growth. It is shown that the tensile fork is shape optimized in a very perfect way in order to avoid any dangerous localized stress peaks (notch stresses) which could lead to failure of the tree.     

Fallenbewegungen fleischfressender Pflanzen

How carnivorous plants outsmart their prey The non‐muscular movements of plants, especially the fast traps of carnivorous plants, might appear as natural “wonders”, but they are all evoked by the interplay of functional morphological structures developed during evolution with well‐described biophysical and chemical processes. Hydraulic “motors”, which are based on water displacement in the respective cells and tissues, entail rather slow motions. Large and fast structures, as e.g., the snap‐traps of the carnivorous Venus flytrap, often depend on the release of stored elastic energy (relaxation) which acts as a speed boost and significantly speeds up the motion. The fast traps presented here and the deformation principles involved, including some mechanical “tricks”, can be rebuild in simple and low‐cost physical models which are especially useful for an application in teaching.     

Molecular study of phytoplasmas associated with pistachio yellows in Iran

A large‐scale survey was conducted on pistachio plants exhibiting foliar symptoms including scorch, little leaf, yellows and reddish in pistachio growing areas in the Qom, Yazd and Qazvin provinces of Iran. Total DNA was extracted from symptomatic and symptomless pistachio and used in nested PCR assays with phytoplasma universal primers. Nested PCR products were obtained for symptomatic plant samples while the symptomless plants yielded no PCR products. Virtual restriction fragment length polymorphism, phylogenetic and DNA homology analyses of partial 16S ribosomal sequences of phytoplasma strains associated with symptomatic plants revealed the presence of phytoplasmas referable to two ribosomal groups; in particular, “Candidatus Phytoplasma solani” and “Ca. P. phoenicium” were identified. The presence of these phytoplasmas in pistachio is of great phytosanitary significance due to its commercial interest.     

SAFETY FACTORS IN VERTICAL STEMS: EVIDENCE FROM EQUISETUM HYEMALE

Predictions from a mechanical model for hollow vertical stems are tested against morphometric and mechanical studies of the vertical stems of Equisetum hyemale. The model predicts 1) that the wall thickness of hollow internodes must be at least 15% of the external radius of shoots, 2) that the elastic modulus of stems is quantitatively related to the ratio of apoplast (cell walls) to symplast (cytoplasm) areas in transverse sections through stems, and that (3) hollow stems are designed to sustain an additional and significant proportion of their own weight. The “safety factors” predicted for a hollow vertical stem are used to examine two adaptationist explanations for hollow stems: 1) “economy in design,” which argues that natural selection will favor a reduction in the metabolic cost in constructing an organ, and 2) “mechanical design,” which argues that stems are designed to maximize their mechanical stability during vertical growth. Evidence from E. hyemale indicates that 1) there is a developmental limit to the maximum allotment of biomass invested in the construction of stems, 2) as stem height increases, morphometric adjustments in internodal wall thickness occur which converge on predicted safety limits, and 3) the elastic modulus of stems changes as a function of the ratio of apoplast to symplast areas seen in transverse sections through shoots. Biomechanical and developmental evidence and the allometry of E. hyemale stems are consistent with the view that stems are designed for safety and are inconsistent with some predictions based on the economy in design.     

Aboriginal New World epidemiology and medical care,and the impact of Old World disease imports

Various workers, including T. D. Stewart, claim that the aboriginal Americas were relatively disease-free because of the Bering Strait cold-screen, eliminating many pathogens, and the paucity of zoonotic infections because of few domestic animals. Evidence of varying validity suggests that precontact Americans had their own strains of treponemic infections, bacillary and amoebic dysenteries, influenza and viral pneumonia and other respiratory diseases, salmonellosis and perhaps other food poisoning, various arthritides, some endoparasites such as the ascarids, and several geographically circumscribed diseases such as the rickettsial verruca (Carrion's disease) and New World leishmaniasis and trypanosomiasis. Questionably aboriginal are tuberculosis and typhus. Accordingly, virtually all the “crowd-type” ecopathogenic diseases such as smallpox, yellow fever, typhoid, malaria, measles, pertussis, polio, etc., appear to have been absent from the New World, and were only brought in by White conquerors and their Black slaves. My hypothesis is that native American medical care systems—especially in the more culturally advanced areas—were sufficiently sophisticated to deal with native disease entities with reasonable competence. But native medical systems could not cope with the “crowd-type” disease imports that struck Indian and Eskimos as “virgin field” populations. Reanalysis of native population losses through a genocidal combination of disease, war, slavery and attendant cultural disruption by Dobyns, Cook and others strongly suggest that traditional estimates underplayed the death toll by a factor of the general order of ten. This would make for an immediately pre-contact Indian population of some 90–111 million instead of the traditional 8–11 million. Evidence is growing that Indians may have been no more susceptible to new pathogens than are other “virgin soil” populations, and thus their immune systems need not be considered less effective than those in other people. Present-day high mortality rates in Indians of both continents from infectious disease imports may be more socioeconomic than anything else.     

THE EVOLUTION OF COSTLY MATE PREFERENCES II. THE “HANDICAP” PRINCIPLE

We use a general additive quantitative genetic model to study the evolution of costly female mate choice by the “handicap” principle. Two necessary conditions must be satisfied for costly preference to evolve. The conditions are (i) biased mutation pressure on viability and (ii) a direct relationship between the degree of expression of the male mating character and viability. These two conditions explain the success and failure of previous models of the “handicap” principle. Our model also applies to other sources of fitness variation like migration and host-parasite coevolution, which cause effects equivalent to biased mutation.     

The role of temporal sensing in bioelectromagnetic effects

Experiments were conducted to see whether the cellular response to electromagnetic (EM) fields occurs through a detection process involving temporal sensing. L929 cells were exposed to 60 Hz magnetic fields and the enhancement of ornithine decarboxylase (ODC) activity was measured to determine cellular response to the field. In one set of experiments, the field was turned alternately off and on at intervals of 0.1 to 50 s. For these experiments, field coherence was maintained by eliminating the insertion of random time intervals upon switching. Intervals ≥ 1 s produced no enhancement of ODC activity, but fields switched at intervals ≥ 10 s showed ODC activities that were enhanced by a factor of approximately 1.7. These data indicate that it is the interval over which field parameters (e.g., amplitude or frequency) remain constant, rather than the interval over which the field is coherent, that is critical to cellular response to an EMF. In a second set of experiments, designed to determine how long it would take for cells to detect a change in field parameters, the field was interrupted for brief intervals (25–200 ms) once each second throughout exposure. In this situation, the extent of EMF-induced ODC activity depended upon the duration of the interruption. Interruptions ≥ 100 ms were detected by the cell as shown by elimination of field-induced enhancement of ODC. That two time constants (0.1 and 10 s) are involved in cellular EMF detection is consistent with the temporal sensing process associated with bacterial chemotaxis. By analogy with bacterial temporal sensing, cells would continuously sample and average an EM field over intervals of about 0.1 s (the “averaging” time), storing the averaged value in memory. The cell would compare the stored value with the current average, and respond to the EM field only when field parameters remain constant over intervals of approximately 10 s (the “memory” time). Bioelectromagnetics 18:388–395, 1997. © 1997 Wiley-Liss, Inc.     

The Growth Response of the Stems of Genetically Modified Tobacco Plants (Nicotiana tabacum'Samsun') to Flexural Stimulation

Genetically modified tobacco plants (Nicotiana tabacum‘Samsun’)with antisense cinnamyl alcohol dehydrogenase DNA, produce secondaryxylem of a reduced tensile stiffness. These plants were grownalongside control plants. The stems of the plants were flexedor protected from flexing over a period of several weeks. Thetensile moduli and second moments of areas of the differenttissues inside the stems were measured and used to calculatethe bending stiffness of the plants. In tobacco, the cylinderof xylem was found to be the most important tissue in determiningthe bending stiffness of the plants. The thickness of the xylemtissue cylinder increased when plants were subjected to flexuralstimulation. This increased the bending stiffness of the stems.The response to mechanical stimulation was found to be correlatedwith tissue strain and the genetically modified plants wereable to exactly compensate for the reduced modulus of theirxylem tissue by increasing the thickness of the xylem tissuecylinder more than in control plants.Copyright 1999 Annals ofBotany Company. Tobacco plants, stem bending, xylem tissue, second moment of area, thigmomorphogenesis, mechanical strain.     

Crystal structure of DszC from Rhodococcus sp. XP at 1.79 Å

The dibenzothiophene (DBT) monooxygenase DszC, which is the key initiating enzyme in “4S” metabolic pathway, catalyzes sequential sulphoxidation reaction of DBT to DBT sulfoxide (DBTO), then DBT sulfone (DBTO₂). Here, we report the crystal structure of DszC from Rhodococcus sp. XP at 1.79 Å. Intriguingly, two distinct conformations occur in the flexible lid loops adjacent to the active site (residue 280–295, between α9 and α10). They are named “open”' and “closed” state respectively, and might show the status of the free and ligand‐bound DszC. The molecular docking results suggest that the reduced FMN reacts with an oxygen molecule at C4a position of the isoalloxazine ring, producing the C4a‐(hydro)peroxyflavin intermediate which is stabilized by H391 and S163. H391 may contribute to the formation of the C4a‐(hydro)peroxyflavin by acting as a proton donor to the proximal peroxy oxygen, and it might also be involved in the protonation process of the C4a‐(hydro)xyflavin. Site‐directed mutagenesis study shows that mutations in the residues involved either in catalysis or in flavin or substrate‐binding result in a complete loss of enzyme activity, suggesting that the accurate positions of flavin and substrate are crucial for the enzyme activity. Proteins 2014; 82:1708–1720. © 2014 Wiley Periodicals, Inc.     

Growth and fecundity of fertile Miscanthus × giganteus (“PowerCane”) compared to feral and ornamental Miscanthus sinensis in a common garden experiment: Implications for invasion

Perennial grasses are promising candidates for bioenergy crops, but species that can escape cultivation and establish self‐sustaining naturalized populations (feral) may have the potential to become invasive. Fertile Miscanthus × giganteus, known as “PowerCane,” is a new potential biofuel crop. Its parent species are ornamental, non‐native Miscanthus species that establish feral populations and are sometimes invasive in the USA. As a first step toward assessing the potential for “PowerCane” to become invasive, we documented its growth and fecundity relative to one of its parent species (Miscanthus sinensis) in competition with native and invasive grasses in common garden experiments located in Columbus, Ohio and Ames, Iowa, within the targeted range of biofuel cultivation. We conducted a 2‐year experiment to compare growth and reproduction among three Miscanthus biotypes—”PowerCane,” ornamental M. sinensis, and feral M. sinensis—at two locations. Single Miscanthus plants were subjected to competition with a native grass (Panicum virgatum), a weedy grass (Bromus inermis), or no competition. Response variables were aboveground biomass, number of shoots, basal area, and seed set. In Iowa, all Miscanthus plants died after the first winter, which was unusually cold, so no further results are reported from the Iowa site. In Ohio, we found significant differences among biotypes in growth and fecundity, as well as significant effects of competition. Interactions between these treatments were not significant. “PowerCane” performed as well or better than ornamental or feral M. sinensis in vegetative traits, but had much lower seed production, perhaps due to pollen limitation. In general, ornamental M. sinensis performed somewhat better than feral M. sinensis. Our findings suggest that feral populations of “PowerCane” could become established adjacent to biofuel production areas. Fertile Miscanthus × giganteus should be studied further to assess its potential to spread via seed production in large, sexually compatible populations.     

Development and Growth Form of the Neotropical Liana <Emphasis Type="Italic">Croton nuntians</Emphasis>: The Effect of Light and Mode of Attachment on the Biomechanics of the Stem

The neotropical liana Croton nuntians (Euphorbiaceae) can occur in a variety of different growth habits. Juvenile freestanding plants are mechanically stable without support and resemble morphologically young trees or shrubs, whereas adult plants are climbers. Ontogenetic variation of bending and torsion properties of different growth phases are analyzed by measurements of flexural stiffness, structural bending modulus, torsional stiffness and structural torsional modulus. Mechanical and anatomical data show two fundamentally different patterns for juvenile freestanding and adult climbing plants. In freestanding plants, mechanical properties and the contribution of cortex, wood, and pith to the stem cross-section vary only little during ontogeny as is typical for semi-self-supporting plants. In contrast, climbing plants become significantly more flexible during ontogeny, as is characteristic for lianas. This is accompanied by a transition to the formation of a less dense wood type with large diameter vessels and an increasing contribution of flexible tissues (less dense wood and cortex) to the cross-sectional area and the axial second moment of area of the stems. Depending on the environmental conditions, freestanding plants can differ considerably in their appearance due to differences in branching system or stem taper. Therefore the influence of light quantity, measured as percentage of canopy opening, on the mechanical properties and the stem anatomy was tested. Freestanding plants grown with strong shade are significantly more stiff in bending compared with plants grown with a moderate light environment.     

Effects of seismic stress on the vegetative growth of Glycine max (L.) Merr. cv. Wells II

Abstract. Vegetative plants of soybean [ Glycine max (L.) Merr. cv. Wells II] grown in a greenhouse and agitated periodically on a gyratory shaker had shorter stems, less leaf area, and lower leaf and plant dry weight than did undisturbed greenhouse-grown (GG) plants after 16 d of treatment. Outdoor-grown (OG) plants, which were subjected to additional environmental stresses including ultraviolet radiation, wind loading, and uncontrolled temperature and humidity fluctuations, were smaller and had less dry weight than GG controls, but growth was not inhibited further by gyratory shaking. Periodic shaking of GG soybeans resulted in the same plant and leaf dry weight as for OG soybeans. Response of GG plants to mechanical stress depended on light intensity, with minimum growth reduction occurring under full light (FL) level, and maximum growth reduction occurring under lower light levels (24–45% FL). Reduction in dry weight gain due to mechanical stress corresponded to a decrease in relative growth rate (RGR). Decreases in net assimilation rate and leaf area ratio contributed equally to the lower RGR of shaken plants, indicating that seismic stress inhibits dry weight accumulation by decreasing both the photosynthetic efficiency and the assimilatory surface of soybean.     

PHYLOGENETIC AFFINITIES OF “CHANTRANSIA” STAGES IN MEMBERS OF THE BATRACHOSPERMALES AND THOREALES (RHODOPHYTA)1

This study evaluated the phylogenetic relationship among samples of “Chantransia” stage of the Batrachospermales and Thoreales from several regions of the world based on sequences of two genes—the plastid‐encoded RUBISCO LSU gene (rbcL) and the nuclear SSU ribosomal DNA gene (SSU rDNA). All sequences of “Chantransia macrospora” were shown to belong to Batrachospermum macrosporum based on both molecular markers, confirming evidence from previous studies. In contrast, nine species are now associated with “Chantransia pygmaea,” including seven species of the Batrachospermales and two of the Thoreales. Therefore, the presence of “C. macrospora” in a stream can be considered reliable evidence that it belongs to B. macrosporum, whereas the occurrence of “C. pygmaea” does not allow the recognition of any particular species, since it is associated with at least nine species. Affinities of “Chantransia” stages to particular taxa were congruent for 70.5% of the samples comparing the rbcL and SSU analyses, which were associated with the same or closely related species for both markers. Sequence divergences have been reported in the “Chantransia” stage in comparison to the respective gametophyte, and this matter deserves further attention.     

Associational resistance,gall-fly preferences,and a stem dimorphism in Solidago altissima

In most populations of Solidago altissima, a small proportion of plants have a growth pattern in which the stem bends early in the season so that the apex is pointing downward (i.e., a “candy-cane” stem) then straightens up again later in the season. The majority of plants, however, do not show this pattern. Instead their stems remain erect from emergence through flowering and senescence. It has recently been shown that the candy-cane stems are a result of a ducking strategy that reduces the risk of attack by apex-attacking herbivores. With such a resistance advantage, it is unclear why the candy-cane morphology is always in the minority, and why the erect morphology persists at all in S. altissima populations. In this study, we tested the hypothesis that the advantage of ducking is inversely frequency dependent and thus will not be an effective resistance strategy when ducking plants are in the majority. In a series of trials, we introduced gall flies (Eurosta solidaginis) into enclosures with relatively low (15%) and relatively high (85%) frequencies of candy-cane versus erect stems. Candy-cane stems were more resistant than erect stems regardless of relative frequency; thus, the hypothesis was rejected. Overall, attack rates were lower for both stem types in the high candy-cane frequency groups than in the low candy-cane frequency groups. This frequency-dependent attack rate suggests that erect-stemmed plants gain “associational resistance” by having a majority of candy-cane neighbors, while candy-cane plants suffer from “associational susceptibility” when surrounded by erect-stemmed neighbors.     

Identification of key microhabitats for fish assemblages in tropical Brazilian savanna streams

The habitat use by stream fish can provide an understanding of this important component of species niches, and the changes in the availability of certain structures of instream habitats have a strong influence on the occurrence and abundance of fish species. In this study, we identified the interaction networks between fish and microhabitats in 19 streams of three watersheds from the Brazilian savanna, known as the “Cerrado”. We also investigated whether the connectance between fish species and microhabitats depends on either the species abundance or availability of microhabitats and verified whether the use of stream microhabitats vary among watersheds. The data for the fish were obtained using standardized fish collections and underwater (snorkeling) observations to record the association of fish species with 11 stream microhabitats. We used the incidence data to calculate the connectance of species with different microhabitats, a Spearman correlation analysis to test the dependence of the connectance to the species abundance and microhabitat availability, and an Analysis of Similarity to test whether the use of stream microhabitats by fish can vary among watersheds. In all of the watersheds, the tetras of the family Characidae used the largest number of microhabitats. The most‐used microhabitats by the fish watersheds were the lateral surface, column surface, and unconsolidated substrate, which were differentially used by the fish in each watershed, indicating the variable importance of microhabitats. Despite this observation, the fish occurred more frequently in the lateral microhabitats. When the data for all of the streams were combined, the species connectance was correlated with the species abundance. We also discuss the consequences of the elimination of certain bottom structures in the context of siltation, which is the main issue in the studied region. The results of our study allowed the detection of key microhabitat structures and can be used for the aquatic ecosystems restoration. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Contributions to the Biomechanics of Plants.; II. Stability Against Local Buckling in Hollow Plant Stems*

Hollow plant stems are, compared to solid ones, endangered by a particular kind of mechanical damage: local buckling. In upright stems centric forces due to the weight of the plant itself are not critical. Bending, however, as caused by wind forces causes transverse stresses that lead to local buckling, long before the critical tension or compression stresses are reached. A new numerical method is proposed to treat local buckling of hollow plant stems caused by bending forces. The results emphasize the importance of transverse reinforcements in the nodes and/or the nodal thickenings for the stability of hollow structures.     

Cryobehavior of the plasma membrane in protoplasts isolated from cold-acclimated Arabidopsis leaves is related to surface area regulation

Extracellular freezing in plants results in dehydration and mechanical stresses upon the plasma membrane. Plants that acquire enhanced freezing tolerance after cold acclimation can withstand these two physical stresses. To understand the tolerance to freeze-induced physical stresses, the cryobehavior of the plasma membrane was observed using protoplasts isolated from cold-acclimated Arabidopsis thaliana leaves with the combination of a lipophilic fluorescent dye FM 1-43 and cryomicroscopy. We found that many vesicular structures appeared in the cytoplasmic region near the plasma membrane just after extracellular freezing occurred. These structures, referred to as freeze-induced vesicular structures (FIVs), then developed horizontally near the plasma membrane during freezing. There was a strong correlation between the increase in individual FIV size and the decrease in the surface area of the protoplasts during freezing. Some FIVs fused with their neighbors as the temperature decreased. Occasionally, FIVs fused with the plasma membrane, which may be necessary to relax the stress upon the plasma membrane during freezing. Vesicular structures resembling FIVs were also induced when protoplasts were mechanically pressed between a coverslip and slide glass. Fewer FIVs formed when protoplasts were subjected to hyperosmotic solution, suggesting that FIV formation is associated with mechanical stress rather than dehydration. Collectively, these results suggest that cold-acclimated plant cells may balance membrane tension in the plasma membrane by regulating the surface area. This enables plant cells to withstand the direct mechanical stress imposed by extracellular freezing.     

Rapid detection of “Candidatus Phytoplasma mali” by recombinase polymerase amplification assays

Isothermal recombinase polymerase amplification (RPA) assays for the specific detection of “Candidatus Phytoplasma mali (Ca. P. mali),” the causal agent of apple proliferation, were developed. The assays amplify a fragment of the imp gene and amplimers were detected either by fluorescence in real‐time mode (TwistAmp^®exo assay) using a fluorophore‐labelled probe or by direct visualization employing a lateral flow device (TwistAmp^®nfo assay/Milenia^®HybriDetect). The RPA assays specifically amplified DNA from “Ca. P. mali” strains, and cross‐reactivity with other phytoplasmas or plant DNA was not observed. The limit of detection was determined with a cloned imp standard, and positive results were obtained down to 10 copies with both RPA assay formats. In comparison with a TaqMan real‐time PCR assay based on the same target gene, the RPA assays were equally sensitive, but results were obtained faster. Simplified nucleic acid extraction procedures from plant tissue with Tris‐ and CTAB‐based buffers revealed that crude Tris–DNA extracts were a suitable source for RPA tests while larger concentrations of CTAB were inhibitory. This is the first report of RPA‐based assays for the detection of “Ca. P. mali”. The assays are suitable for high‐throughput screening of plant material and point‐of‐care diagnostic and can be potentially combined with a simplified DNA extraction procedure.