Adaptations to increasing hydraulic stress: morphology, hydrodynamics and fitness of two higher aquatic plant species

Sessile organisms often exhibit morphological changes in response to permanent exposure to mechanical stimulation (wind or water movements). The adaptive value of these morphological changes (hydrodynamic performance and consequences on fitness) has not been studied extensively, particularly for higher plants submitted to flow stress. The aim was to determine the adaptive value of morphological patterns observed within two higher aquatic plant species, Berula erecta and Mentha aquatica, growing along a natural flow stress gradient. The hydrodynamic ability of each ramet was investigated through quantitative variables (drag coefficient and E-value). Fitness-related traits based on vegetative growth and clonal multiplication were assessed for each individual. For both species, the drag coefficient and the E-value were explained only to a limited extent by the morphological traits used. B. erecta exhibited a reduction in size and low overall plant drag at higher flow velocities, despite high drag values relative to leaf area, due to a low flexibility. The plants maintained their fitness, at least in part, through biomass reallocation: one tall ramet at low velocity, but shorter individuals with many interconnected stolons when flow velocity increased. For M. aquatica, morphological differences along the velocity gradient did not lead to greater hydrodynamic performance. Plant size increased with increasing velocities, suggesting the indirect effects of current favouring growth in high velocities. The fitness-related traits did not demonstrate lower plant fitness for high velocities. Different developmental constraints linked to plant morphology and trade-offs between major plant functions probably lead to different plant responses to flow stress.     

VARIATION IN ANATOMICAL AND MATERIAL PROPERTIES EXPLAINS DIFFERENCES IN HYDRODYNAMIC PERFORMANCES OF FOLIOSE RED MACROALGAE (RHODOPHYTA)1

Over the last two decades, many studies on functional morphology have suggested that material properties of seaweed tissues may influence their fitness. Because hydrodynamic forces are likely the largest source of mortality for seaweeds in high wave energy environments, tissues with material properties that behave favorably in these environments are likely to be selected for. However, it is very difficult to disentangle the effects of materials properties on seaweed performance because size, shape, and habitat also influence mechanical and hydrodynamic performance. In this study, anatomical and material properties of 16 species of foliose red macroalgae were determined, and their effects on hydrodynamic performance were measured in laboratory experiments holding size and shape constant. We determined that increased blade thickness (primarily caused by the addition of medullary tissue) results in higher flexural stiffness (EI), which inhibits the seaweed’s ability to reconfigure in flowing water and thereby increases drag. However, this increase is concurrent with an increase in the force required to break tissue, possibly offsetting any risk of failure. Additionally, while increased nonpigmented medullary cells may pose a higher metabolic cost to the seaweed, decreased reconfiguration causes thicker tissues to expose more photosynthetic surface area incident to ambient light in flowing water, potentially ameliorating the metabolic cost of producing these cells. Material properties can result in differential performance of morphologically similar species. Future studies on ecomechanics of seaweeds in wave‐swept coastal habitats should consider the interaction of multiple trade‐offs.     

A three‐dimensional numerical model investigation of the impact of submerged macrophytes on flow dynamics in a large fluvial lake

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Computational modeling of shear forces and experimental validation of endothelial cell responses in an orbital well shaker system

Vascular endothelial cells are continuously exposed to hemodynamic shear stress. Intensity and type of shear stress are highly relevant to vascular physiology and pathology. Here, we modeled shear stress distribution in a tissue culture well (R = 17.5 mm, fill volume 2 ml) under orbital translation using computational fluid dynamics with the finite element method. Free surface distribution, wall shear stress, inclination angle, drag force, and oscillatory index on the bottom surface were modeled. Obtained results predict nonuniform shear stress distribution during cycle, with higher oscillatory shear index, higher drag force values, higher circular component, and larger inclination angle of the shear stress at the periphery of the well compared with the center of the well. The oscillatory index, inclination angle, and drag force are new quantitative parameters modeled in this system, which provide a better understanding of the hydrodynamic conditions experienced and reflect the pulsatile character of blood flow in vivo. Validation experiments revealed that endothelial cells at the well periphery aligned under flow and increased Kruppel-like Factor 4 (KLF-4), cyclooxygenase-2 (COX-2) expression and endothelial nitric oxide synthase (eNOS) phosphorylation. In contrast, endothelial cells at the center of the well did not show clear directional alignment, did not induce the expression of KLF-4 and COX-2 nor increased eNOS phosphorylation. In conclusion, this improved computational modeling predicts that the orbital shaker model generates different hydrodynamic conditions at the periphery versus the center of the well eliciting divergent endothelial cell responses. The possibility of generating different hydrodynamic conditions in the same well makes this model highly attractive to study responses of distinct regions of the same endothelial monolayer to different types of shear stresses thereby better reflecting in vivo conditions.     

The influence of gravity and wind on land plant evolution

Aspects of the engineering theory treating the elastic stability of vertical stems and cantilevered leaves supporting their own weight and additional wind-induced forces (drag) are reviewed in light of biomechanical studies of living and fossil terrestrial plant species. The maximum height to which arborescent species can grow before their stems elastically buckle under their own weight is estimated by means of the Euler-Greenhill formula which states that the critical buckling height scales as the 1/3 power of plant tissue-stiffness normalized with respect to tissue bulk density and as the 2/3 power of stem diameter. Data drawn from living plants indicate that progressively taller plant species employ stiffer and lighter-weight plant tissues as the principal stiffening agent in their vertical stems. The elastic stability of plants subjected to high lateral wind-loadings is governed by the drag torque (the product of the drag force and the height above ground at which this force is applied), which cannot exceed the gravitational bending moment (the product of the weight of aerial organs and the lever arm measured at the base of the plant). Data from living plants indicate that the largest arborescent plant species rely on massive trunks and broad, horizontally expansive root crowns to resist drag torques. The drag on the canopies of these plants is also reduced by highly flexible stems and leaves composed of tissues that twist and bend more easily than tissues used to stiffen older, more proximal stems. A brief review of the fossil record suggests that modifications in stem, leaf, and root morphology and anatomy capable of simultaneously coping with self-weight and wind-induced drag forces evolved by Devonian times, suggesting that natural selection acting on the elastic stability of sporophytes occurred early in the history of terrestrial plants.     

Settlement of the diazotrophic,phytoeffective bacterial strain Pantoea agglomerans on and within winter wheat: An investigation using ELISA and transmission electron microscopy

The aim of this study was to investigate the ability of Pantoea agglomerans, a plant growth-promoting bacterium, to colonize various regions and tissues of the wheat plant (Triticum aestivum L.) by using different inoculation methods and inoculum concentrations. In addition, the enzyme-linked immunosorbent assay (ELISA) and transmission electron microscopy (TEM) were used to determine: (a) the ability of the bacterial cells to grow and survive both on the surface and within internal tissue of the plant and (b) the response of the plant to bacterial infection. After inoculation, cells of the diazotrophic bacterial strain P. agglomerans were found to be located in roots, stems and leaves. Colony development of bacterial cells was only detected within intercellular spaces of the root and on the root surface. However, single bacterial cells were observed in leaves and stems on the surface of the epidermis, in the vicinity to stomatal cells, within intercellular spaces of the mesophyll and within xylem vessels. Inoculated bacterial cells were found to be able to enter host tissues, to multiply in the plant and to maintain a delicate relationship between endophyte and host. The density of bacterial settlement in the plant in all experiments was about 10⁶ to 10⁷ cells per mL root or shoot sap. Establishment was confirmed by a low coefficient of variation of ELISA means at these concentrations.     

Biological characterization of the skin of shortfin mako shark Isurus oxyrinchus and preliminary study of the hydrodynamic behaviour through computational fluid dynamics

This study characterized the morphology, density and orientation of the dermal denticles along the body of a shortfin mako shark Isurus oxyrinchus and identified the hydrodynamic parameters of its body through a computational fluid‐dynamics model. The study showed a great variability in the morphology, size, shape, orientation and density of dermal denticles along the body of I. oxyrinchus. There was a significant higher density in dorsal and ventral areas of the body and their highest angular deviations were found in the lower part of the mouth and in the areas between the pre‐caudal pit and the second dorsal and pelvic fins. A detailed three‐dimensional geometry from a scanned body of a shark was carried out to evaluate the hydrodynamic properties such as drag coefficient, lift coefficient and superficial (skin) friction coefficient of the skin together with flow velocity field, according to different roughness coefficients simulating the effect of the dermal denticles. This preliminary approach contributed to detailed information of the denticle interactions. As the height of the denticles was increased, flow velocity and the effect of lift decreased whereas drag increased. The highest peaks of skin friction coefficient were observed around the pectoral fins.     

Penetration into rice tissues by brown planthopper and fine structure of the salivary sheaths

The fine structure of the salivary sheaths in plant tissues can provide important information on homopteran probing and ingestion behaviors. Salivary sheaths secreted by the brown planthopper (BPH), Nilaparvata lugens (Stål) (Homoptera: Delphacidae), and their tissue pathway were investigated using light, scanning electron, and transmission electron microscopy. About half of the salivary flanges on the surface of the food substrate were connected with internal salivary sheaths. Only 43% of the salivary sheaths showed side branches. Many sculpture‐like protuberances and small cavities had been formed on the outer surface of the salivary sheath, but the sheath lumen circumferences were sealed. Brown planthoppers showed a preference for probing and leaving salivary sheaths in the susceptible rice variety TN1 rather than in the resistant variety B5 during the first 2 days of the experiments. The salivary sheaths in rice tissues reached the inner tissue layer of the leaf sheaths and stems, but were mostly observed to end in the first and second layer of the leaf sheaths. Brown planthoppers also preferred to probe into the thick segment of the outer leaf sheath. After ingestion by the insect, the cytoplasm in both phloem and companion cells degraded and the main organelles were lost. Numerous small vesicles were found in most of the phloem cells, but cell walls remained intact. Large numbers of symbiont‐like structures were observed inside the salivary sheath lumen. These results indicated that BPH has complicated feeding behaviors, which warrants further investigation.     

Sieve element specific labeling with an anti-idiotypic monoclonal antibody mimic of the phytotoxin dothistromin

A monoclonal antibody, 12C9, an anti-idiotypic mimic of dothistromin, a toxin produced by Dothistroma pini, was found to label the cell wall of sieve elements in a number of different plant tissues and species. The antibody labeled apple leaf tissue, tobacco leaf mid vein, leaf and meristem, and Coprosma robusta leaf mid vein. Labeling was restricted to cell walls of sieve elements and did not label the companion cells or the lumen of the cells. The antibody labeled over a wide range of dilutions. This antibody could be used to differentiate sieve elements from other types of phloem. It could also be used to co-localize sieve elements and microorganisms such as phytoplasmas stained with DAPI.     

Biomechanics of the columnar cactus Pachycereus pringlei

We report the longitudinal variations in stiffness and bulk density of tissue samples drawn from along the length of two Pachycereus pringlei plants measuring 3.69 and 5.9 m in height to determine how different tissues contribute to the mechanical stability of these massive vertical organs. Each of the two stems was cut into segments of uniform length and subsequently dissected to obtain and mechanically test portions of xylem strands, stem ribs, and a limited number of pith and cortex samples. In each case, morphometric measurements were taken to determine the geometric contribution each tissue likely made to the ability of whole stems to resist bending forces. The stiffness of each xylem strand increased basipetally toward the base of each plant where stiffness sharply decreased, reaching a magnitude comparable to that of strands 1 m beneath the stem apex. The xylem was anisotropic in behavior, i.e., its stiffness measured in the radial and in the tangential directions differed significantly. Despite the abrupt decrease in xylem strand stiffness at the stem base, the contribution made by this tissue to resist bending forces increased exponentially from the tip to the base of each plant due to the accumulation of wood. A basipetal increase in the stiffness of the pith (and, to limited extent, that of the cortex) was also observed. In contrast, the stiffness of stem rib tissues varied little as a function of stem length. These tissues were stiffer than the xylem in the corresponding portions of the stem along the upper two-fifths of the length of either plant. Tissue stiffness and bulk density were not significantly correlated within or across tissue types. However, a weak inverse relationship was observed for these properties in the case of the xylem and stem rib tissues. We present a simple formula that predicts when stem ribs rather than the xylem strands serve as the principal stiffening agents in stems. This formula successfully predicted the observed aspect ratio of the stem ribs (the average quotient of the radial and tangential dimensions of rib transections), and thus provided circumstantial evidence that the ribs are important for mechanical stability for the distal and younger regions of the stems examined.     

Functional Imaging of Plants: A Nuclear Magnetic Resonance Study of a Cucumber Plant

Functional magnetic resonance imaging was used to study transients of biophysical parameters in a cucumber plant in response to environmental changes. Detailed flow imaging experiments showed the location of xylem and phloem in the stem and the response of the following flow characteristics to the imposed environmental changes: the total amount of water, the amount of stationary and flowing water, the linear velocity of the flowing water, and the volume flow. The total measured volume flow through the plant stem was in good agreement with the independently measured water uptake by the roots. A separate analysis of the flow characteristics for two vascular bundles revealed that changes in volume flow of the xylem sap were accounted for by a change in linear-flow velocities in the xylem vessels. Multiple-spin echo experiments revealed two water fractions for different tissues in the plant stem; the spin-spin relaxation time of the larger fraction of parenchyma tissue in the center of the stem and the vascular tissue was down by 17% in the period after cooling the roots of the plant. This could point to an increased water permeability of the tonoplast membrane of the observed cells in this period of quick recovery from severe water loss.     

Trubs,but no trianas: filled and empty regions of angiosperm stem length‐diameter‐mechanics space

Discrete plant habit categories such as ‘tree’, ‘shrub’, and ‘liana’ belie continuous variation in nature. To study the evolution of this continuous variation, we gathered data on stem length, diameter and tissue mechanical stiffness across a highly morphologically diverse highland xerophytic scrub on a lava flow in central Mexico. With stem allometric and mechanical data from 1216 segments from 50 species, we examined relationships between stem length–diameter proportions and tissue mechanical stiffness using linear mixed‐effects models. Rather than a series of discrete clouds in stem length–diameter–tissue stiffness space, corresponding to traditional habit categories, the plants of this xerophytic scrub formed a single continuous one. Within this cloud, self‐supporting plants had stems that became predictably longer and tissues that became stiffer for a given diameter increase, and there was no paucity of intermediates between trees and shrubs (‘trubs’). Non self‐supporting plants had a steeper stem length–diameter slope and their tissues did not increase in stiffness with stem size. The area between self‐ and non self‐supporting plants was sparsely occupied as stem size increased. We predict that this ‘empty’ space between lianas and trees is developmentally accessible but of low fitness, meaning that there should be few ‘trianas’ in nature. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179 , 361–373.     

Reazioni delle piante di Ricinus communis a incisioni sperimentali

Summary

The author has produced wounds in the stem of Ricinus communis, studing the regeneration and cicatrization processes.

The rapidity of the surface cicatrization is in relation with the water loss of the waunded cells.

Both in the stems woumded let free and in those in which an extra tissue has been introduced, the cicatrization processes tacke place. They only take place with different velocity. The healing process lead to the reconstruction of the cortical and the conducting tissues.

The whole reconstruction of the stele may occur, when the flow of the assimilated stuffs is slowed. Sothat it is probable that the regeneration depends more upon the tissue nutrition tham on a specifical properti of the tissues.     

Tissue specific protochlorophyll(ide) forms in dark-forced shoots of grapevine (<Emphasis Type="Italic">Vitis vinifera</Emphasis>L.)

Cuttings of grapevine (Vitis vinifera L. cv. Chardonnay) were dark-forced at least three weeks. Pigment contents, 77 K fluorescence emission, excitation spectra of the leaves, petioles, stems, transmission electron micrographs of the etioplasts from leaves, the chlorenchyma tissues of the stems were analysed. The dark-grown leaves, stems contained 8 to 10, 3 to 5 μg/g fresh weight protochlorophyllide, its esters, respectively. HPLC analysis showed that the molar ratio of the unesterified, esterified pigments was 7:3 in the shoot developed in darkness. The dark-forced leaves contained carotenoids identified as: neoxanthin, violaxanthin, antheraxanthin, lutein, β-carotene. Detailed analyses of the fluorescence spectra proved that all tissues of the dark-forced shoots had protochlorophyllide or protochlorophyll forms with emission maxima at 628, 636, 644, 655, 669 nm. The 628, 636 nm emitting forms were present in all parts of the dark-forced shoot, but dominated in the stems, which may indicate an organ specificity of the etioplast development. Variations in the distribution of the pigment forms were even found in the different tissues of the stem. The subepidermal layers were more abundant in the 655 nm form than the parenchyma cells of the inner part of the cortex, the pith. In the latter cells, the plastid differentiation stopped in intermediary stages between proplastids, etioplasts. The plastids in the subepidermal layers had developed prolamellar body structures, which were similar to those of etiolated leaves. The results highlight the importance of organ-, tissue specificity of plastid differentiation for chlorophyll biosynthesis, greening of different plant organs. This revised version was published online in June 2006 with corrections to the Cover Date.     

Optimizing the medium perfusion rate in bone tissue engineering bioreactors

There is a critical need to increase the size of bone grafts that can be cultured in vitro for use in regenerative medicine. Perfusion bioreactors have been used to improve the nutrient and gas transfer capabilities and reduce the size limitations inherent to static culture, as well as to modulate cellular responses by hydrodynamic shear. Our aim was to understand the effects of medium flow velocity on cellular phenotype and the formation of bone‐like tissues in three‐dimensional engineered constructs. We utilized custom‐designed perfusion bioreactors to culture bone constructs for 5 weeks using a wide range of superficial flow velocities (80, 400, 800, 1,200, and 1,800 µm/s), corresponding to estimated initial shear stresses ranging from 0.6 to 20 mPa. Increasing the flow velocity significantly affected cell morphology, cell–cell interactions, matrix production and composition, and the expression of osteogenic genes. Within the range studied, the flow velocities ranging from 400 to 800 µm/s yielded the best overall osteogenic responses. Using mathematical models, we determined that even at the lowest flow velocity (80 µm/s) the oxygen provided was sufficient to maintain viability of the cells within the construct. Yet it was clear that this flow velocity did not adequately support the development of bone‐like tissue. The complexity of the cellular responses found at different flow velocities underscores the need to use a range of evaluation parameters to determine the quality of engineered bone. Bioeng. 2011; 108:1159–1170. © 2010 Wiley Periodicals, Inc.     

Insights into carotenoid dynamics in non‐foliar photosynthetic tissues of avocado

Leaves are the main photosynthetically active tissues in most plants. However, stems and fruits are also important for the overall carbon balance of the plant because of their contribution to fixation of the CO₂ released by respiration. Photosynthesis could not be possible without a complete set of photoprotection mechanisms, which include the ubiquitous violaxanthin (V) cycle and the taxonomically restricted lutein epoxide (Lx) cycle. In this work, we characterise carotenoid stoichiometry in photosynthetic stems and fruits of avocado in comparison with that of leaves and specifically whether Lx is present in these tissues and also whether it is involved in a light‐driven cycle. Avocado was selected as model species to study whether both cycles were functional in non‐foliar photosynthetic structures (stems and fruits). An unusual pigment composition was observed in avocado fruit, with a high content of cis‐V and cis‐Lx, suggesting a different photosynthetic function. In stems, both xanthophylls de‐epoxidated upon illumination, but only V recovered in the dark, indicating the existence of a possible ‘truncated’ Lx cycle. Lx in fruits was de‐epoxidated only when its pool was higher than a threshold of 30 mmol mol^?1 chlorophyll, indicating a high non‐photoconvertible pool of Lx. We conclude that, at least in stems, the dynamic regulation of photosynthetic activity could also depend on the Lx cycle.     

Reconfiguration as a Prerequisite for Survival in Highly Unstable Flow-Dominated Habitats

Unstable and mechanically demanding habitats like wind-exposed open fields or the wave-swept intertidal require rapid adaptive processes to ensure survival. The mechanism of passive reconfiguration was analyzed in two plant models exposed to irregular flow of water or air, two species of the brown seaweed Durvillaea and the giant reed Arundo donax. Irrespective of the surrounding media and the subsequent Reynolds numbers (Re ~ 10⁵ - 10⁷), reconfiguration seems to be the key strategy for streamlining to avoid overcritical drag-induced loads. This passive mechanism is also discussed in the context of the requirement of a maximized surface area for light interception, so that morphological adaptations to rapid reconfiguration represent at least a bifactorial optimization. Both tested plant models exhibited the same principles in streamlining. At a specific threshold value, the proportionality between drag forces and flow velocity can be reduced from the second power close to an almost linear relation. This empirically derived relation could be characterized by a figure of merit or Vogel number (B). A value close to B = -1, resulting in a linear increase of drag force with velocity, was found at higher velocities for both the seaweeds and the giant reed, as well as for a variety of plants described in the literature. It is therefore concluded that the ability to reduce velocity-dependent drag force to a linear relation is a potentially important adaptation for plants to survive in unstable flow-dominated habitats.     

Attachment strength of an adhesive nuisance mussel,limnoperna fortunei,against water flow

The attachment strength of the freshwater mussel Limnoperna fortunei against water flow was studied. Newton's expression successfully described the hydrodynamic drag force acting on the mussel with a drag coefficient value of 1.03. The drag‐resistant force (defined as hydrodynamic drag force at mussel detachment) was smaller than the detachment force measured using a tensile load test. A fairly good correlation was obtained between the drag‐resistant force and the number of secreted threads. The drag‐resistant force divided by the number of threads increased with shell size, suggesting that byssal thread strength increased with mussel growth. For the mussel specimens obtained from a water transmission pipe, thread width increased with shell size. However, thread width was not dependent on current velocity. There was no correlation between the number of secreted threads and shell length, which indicated that the number of secreted threads did not change with mussel size. Therefore, the water velocity needed to detach mussels increases with shell size of the mussel when the number of secreted threads is constant. The increases in the water velocity to detach mussels with larger shells suggests that the mussel becomes more resistant to water flow as it grows. It is estimated that a flow velocity of around lms^‐1 is critical for attachment/detachment of a juvenile mussel with a shell length of a few millimeters and one hundred byssal threads.     

Variation in basal sprouting in co-occurring shrubs: implications for stand dynamics

Abstract. Sources of basal sprouting for five shrub species representing five plant families common to the Tamaulipan biotic province were quantified, following four intensities of top removal. Among undisturbed shrubs, Celtis pallida and Zanthoxylum fagara were somewhat arborescent, with one or two dominant primary stems per plant. Aloysia gratissima, Ziziphus obtusifolia and Schaefferia cuneifolia were fruticose in architecture, with more and smaller stems. Following top removal, each species exhibited a distinct regenerative hierarchy whereby shoot production following disturbance was primarily from structures immediately subtending the removed tissues, even though more distal tissues had the capacity for shoot production. Thus, removal of stems to a 5 cm residual increased the contribution of primary stems from stem bases, whereas stem removal to ground line typically induced regeneration from root crowns. Schaefferia, Zanthoxylum and Ziziphus were capable of producing shoots from root tissue, yet regeneration from roots was not stimulated until tissues were removed to below root crowns. Field observations indicate that most woody species in the subtropical thorn woodlands of southern Texas, USA, are highly persistent in the face of natural and anthropogenic disturbance, owing to their ability to regenerate vegetatively. Alternative sources of stem replacement contribute to the high resilience of these shrubs following disturbance and may help explain or predict patterns of secondary succession and plant persistence following various intensities of disturbance.