Fig 3 - uploaded by Thomas Speck
Content may be subject to copyright.
Wilting experiments carried out with Caladium bicolor 'Candyland' ; habitus of well-watered plants (day 0); habitus of plants without watering for 4 and 7 d, respectively.
Source publication
Premise of the study:
Cell turgor plays an important role in the mechanical stability of herbaceous plants. This study on petioles of Caladium bicolor 'Candyland' analyzes the correlation between flexural rigidity and cell turgor. The results offer new insights into the underlying form-structure-function relationship and the dependency of mechanic...
Context in source publication
Context 1
... experiments -To obtain petioles showing a wide turgor range in the parenchymatous cells, we set up the plants to wilt under normal laboratory conditions (20 ° C, 50% relative humidity, 07:00-19:00 hours, additional artifi - cial illumination) by removing residual water from the saucer and discontinuing watering. Watered plants and plants not watered for 4 to 15 d were used for the experiments ( Fig. 3 ). Only petioles showing no visible changes in morphology during wilting were selected for testing. ...
Citations
... Turgor pressure significantly influences the mechanical properties of plant tissues, affecting stiffness and elasticity [7]. During water stress, a plant experiences water loss from its cells, resulting in reduced cell turgor pressure [18]. ...
... We conducted a water stress study by placing a 1 g weight on a leaf of a plant (see Figure 3a), and measuring its displacement from its resting position after vibration. Figure 3b shows the overall trend was as expected from the literature [7] where the leaf-stem stiffness decreased with drought stress. Futhermore, the turgor pressure follows daily patterns aligned with the 24-hour day/night cycle, known as the diurnal cycle [1]. ...
... Exploring the mechanical properties of the plant, several studies [7,18,27] have analyzed the bending stiffness of leaves under drought stress, revealing that cell turgor loss contributed to changes in flexural rigidity during water stress conditions. Recent works have specifically explored the frequency patterns of plants under stress, proposing that changes in vibration frequency could serve as indicators of the plant's water status [6,28]. ...
In this paper, we introduce MotionLeaf , a novel mmWave base multi-point vibration frequency measurement system that can estimate plant stress by analyzing the surface vibrations of multiple leaves. MotionLeaf features a novel signal processing pipeline that accurately estimates fine-grained damped vibration frequencies based on noisy micro-displacement measurements from a mmWave radar. Specifically we explore the Interquartile Mean (IQM) of coherent phase differences from neighboring Frequency-Modulated Continuous Wave (FMCW) radar chirps to calculate micro-displacements. Furthermore, we use the measurements from multiple received antennas in the radar to estimate the vibration signals of different leaves via a Blind Source Separation (BSS) method. Experimental results demonstrate that MotionLeaf can accurately measure the frequency of multiple leaves in a plant with average error of 0.0176 Hz, which is less than 50% of that (0.0416 Hz) of the state-of-the-art approach (mmVib). Additionally, the estimated natural vibration frequencies from MotionLeaf are shown to be an excellent feature to detect the water stress in the plant during 7-day drought experiments.
... Previous work in this area explores eigenfrequency [1] or the general reactions to simple manipulation tasks [2]. Interactive perception has also been explored in the context of plants to determine their bending stiffness under different growing conditions [3]. Brüchert et al. describe the oscillations and damping of plant stems in detail [4]. ...
In robotics, when dealing with highly flexible objects like plants, it is often desirable to model their dynamic behaviour for representing and segmenting the surroundings. Plants specifically often tend to exhibit oscillatory motion patterns (e.g. swaying of branches and fluttering of leaves), which are mostly unutilised in state-of-the-art computer vision techniques. In this paper we present a novel approach to motion segmentation based on oscillatory movement of plants, optical flow and frequency based analyses. We combine these individual approaches to form a data processing pipeline producing motion-based segmentation maps highlighting individual plant parts. We test our approach on wheat plants, with the algorithm successfully identifying individual wheat ears that have moved sufficiently as separate clusters, even if unconnected in image space. This highlights the novelty of this approach as well as its advantages over other, more conservative segmentation methods.
... Consequently, herbaceous plants utilize the turgor pressure associated with their internal water content to maintain their rigidity 22,[25][26][27][28][29][30][31][32][33][34] . In herbaceous plants, when the inflow of water exceeds the outflow of water from inside a cell, turgor pressure is generated to equalize the pressure inside and outside the cell. ...
... In herbaceous plants, when the inflow of water exceeds the outflow of water from inside a cell, turgor pressure is generated to equalize the pressure inside and outside the cell. However, when a loss of water occurs as a result of transpiration caused by, for example, stem and branch cutting, or drying, the bending rigidity and the tension force both decrease owing to cross-sectional shrinkage 33 and turgor pressure, respectively; a large deflection occurs instantly 34 . This is thought to be caused not only by a decrease in the bending rigidity of the plant itself because of its drying but also by the loss of the plant's "geometric rigidity", which is maintained by the tension forces associated with turgor pressure. ...
... The above-mentioned results indicate that the tangent model is the most appropriate model for expressing the relationship between K and D R among the regression models shown in Eqs. (31)(32)(33)(34). However, it should be noted that although the tangent model represents the relation very accurately when D R ≥ 90% , it underestimates the value of the parameter K in the range where 0 ≤ D R ≤ 90%. ...
The bodies of herbaceous plants are slender, thin, and soft. These plants support their bodies through the action of turgor pressure associated with their internal water stores. The purpose of this study was to apply the principles of structural mechanics to clarify the underlying mechanism of rigidity control that is responsible for turgor pressure in plants and the reason behind the self-supporting ability of herbaceous plants. We modeled a plant a horizontally oriented thin-walled cylindrical cantilever with closed ends enclosing a cavity filled with water that is acted on by its own weight and by internal tension generated through turgor pressure. We derived an equation describing the plant’s consequent deflection, introducing a dimensionless parameter to express the decrease in deflection associated with the action of turgor pressure. We found that the mechanical and physical characteristics of herbaceous plants that would appear to be counter-productive from a superficial perspective increase the deflection decreasing effect of turgor pressure.
... At full turgor, external stresses are redistributed across the cell walls which results in stiffening of the tissue as a whole [4]. When deprived of water, E values of parenchyma and collenchyma decrease and show a higher flexibility and lower flexural rigidity of the petiole [29]. The impact of the abovementioned fiber bundles in the plant individual of B. amphioxus now becomes apparent as this species shows higher percentages of leaf dry mass and lignified petiolar tissue than the other analyzed species. ...
Plants are exposed to various external stresses influencing physiology, anatomy, and morphology. Shape, geometry, and size of shoots and leaves are particularly affected. Among the latter, peltate leaves are not very common and so far, only few studies focused on their properties. In this case study, four Begonia species with different leaf shapes and petiole attachment points were analyzed regarding their leaf morphology, anatomy, and biomechanical properties. One to two plants per species were examined. In all four species, the petiole showed differently sized vascular bundles arranged in a peripheral ring and subepidermal collenchyma. These anatomical characteristics, low leaf dry mass, and low amount of lignified tissue in the petiole point toward turgor pressure as crucial for leaf stability. The petiole-lamina transition zone shows a different organization in leaves with a more central (peltate) and lateral petiole insertion. While in non-peltate leaves simple fiber branching is present, peltate leaves show a more complex reticulate fiber arrangement. Tensile and bending tests revealed similar structural Young’s moduli in all species for intercostal areas and venation, but differences in the petiole. The analysis of the leaves highlights the properties of petiole and the petiole-lamina transition zone that are needed to resist external stresses.
... Anoline setae are tapered structures and tapering can reduce the effective bending stiffness (k eff ) of the fibres. Based upon work by Caliaro et al. (2013), Garner et al. (2021b) calculated k eff of anoline setae by multiplying the bending stiffness of a fixed radius cylinder (k) by a tapering ratio (t): ...
The subdigital adhesive pads of Caribbean Anolis lizards are considered to be a key innovation that permits occupation of novel ecological niches. Although previous work has demonstrated that subdigital pad morphology and performance vary with habitat use, such investigations have only considered the macroscale aspects of these structures (e.g. pad area). The morphological agents of attachment, however, are arrays of hair-like fibres (setae) that terminate in an expanded tip (spatula) and have not been examined in a similar manner. Here we examine the setal morphology and setal field configuration of ecologically distinct species of the monophyletic Jamaican Anolis radiation from a functional and ecological perspective. We find that anoles occupying the highest perches possess greater setal densities and smaller spatulae than those exploiting lower perches. This finding is consistent with the concept of contact splitting, whereby subdivision of an adhesive area into smaller and more densely packed fibres results in an increase in adhesive performance. Micromorphological evidence also suggests that the biomechanics of adhesive locomotion may vary between Anolis ecomorphs. Our findings indicate that, in a similar fashion to macroscale features of the subdigital pad, its microstructure may vary in relation to performance and habitat use in Caribbean Anolis.
... Figure 2 illustrates various transverse sections of plant axes with differing cross-sectional geometries and tissue patterns. Based on stained thin sections from previous studies [1,21,[23][24][25], corresponding schematic drawings were created depicting the cross-sectional geometry of the plant axes and the distribution of the tissues involved. These plant examples were selected because their geometric, mechanical and structural properties were available for discussion of the results of the simulations of this study (electronic supplementary material, S1 and table S1.1). ...
... Investigations of C. bicolor petioles (figure 2c,d) have revealed that their mechanical properties exhibit a high value of E/ G ≈ 64, resulting in a twist-to-bend ratio of approximately 40 [1] (electronic supplementary material, S1 and table S1.1). The almost circular petioles have in the periphery a median of 66 individual collenchyma strands, which are elliptical in cross-section [23]. By contrast, figure 7b shows that, according to our calculations, 45 collenchyma strands already merge. ...
During the evolution of land plants many body plans have been developed. Differences in the cross-sectional geometry and tissue pattern of plant axes influence their flexural rigidity, torsional rigidity and the ratio of both of these rigidities, the so-called twist-to-bend ratio. For comparison, we have designed artificial cross-sections with various cross-sectional geometries and patterns of vascular bundles, collenchyma or sclerenchyma strands, but fixed percentages for these tissues. Our mathematical model allows the calculation of the twist-to-bend ratio by taking both cross-sectional geometry and tissue pattern into account. Each artificial cross-section was placed into a rigidity chart to provide information about its twist-to-bend ratio. In these charts, artificial cross-sections with the same geometry did not form clusters, whereas those with similar tissue patterns formed clusters characterized by vascular bundles, collenchyma or sclerenchyma arranged as one central strand, as a peripheral closed ring or as distributed individual strands. Generally, flexural rigidity increased the more the bundles or fibre strands were placed at the periphery. Torsional rigidity decreased the more the bundles or strands were separated and the less that they were arranged along a peripheral ring. The calculated twist-to-bend ratios ranged between 0.85 (ellipse with central vascular bundles) and 196 (triangle with individual peripheral sclerenchyma strands).
... In the peel parenchyma cells, the influence of the water content mainly depends on cell wall properties and turgor pressure. Freeze-drying results in dehydration of the entire cell (and cell wall) by sublimating the frozen water from the vacuole, the protoplast and the cell wall matrix [3,24,[36][37][38]. The pressure loss of the individual cells and the contraction stresses are results of the water loss in the tissue. ...
This study analyzes the impact behavior of lemon peel (Citrus x limon) and investigates its functional morphology compared with the anatomy of pomelo peel (Citrus maxima). Both fruit peels consist mainly of parenchyma structured by a density gradient. In order to characterize the lemon peel, both energy dissipation and transmitted force are determined by conducting drop weight tests at different impact strengths (0.15–0.74 J). Fresh and freeze-dried samples were used to investigate the influence on the mechanics of peel tissue’s water content. The samples of lemon peel dissipate significantly more kinetic energy in the freeze-dried state than in the fresh state. Fresh lemon samples experience a higher impulse than freeze-dried samples at the same momentum. Drop weight tests results show that fresh lemon samples have a significantly longer impact duration and lower transmitted force than freeze-dried samples. With higher impact energy (0.74 J) the impact behavior becomes more plastic, and a greater fraction of the kinetic energy is dissipated. Lemon peel has pronounced energy dissipation properties, even though the peel is relatively thin and lemon fruits are comparably light. The cell arrangement of citrus peel tissue can serve as a model for bio-inspired, functional graded materials in technical foams with high energy dissipation.
... Petioles possess various tapering modes (Langer et al., 2021a). Caliaro et al. (2013), showed highly significant differences (P<0.01) when calculating the bending elastic modulus of petioles of Caladium bicolor with the equation considering the tapering mode compared with the equation for untapered cylindrical beams with constant circular cross-section using the mean radius of each petiole (n=54). Because of these significant differences, the tapering mode α will be considered in our calculations of the bending elastic modulus E and the torsional modulus G. ...
... where r l is the radius in lateral direction and r a the radius und adaxial-abaxial direction. According to Caliaro et al. (2013), the tapering mode α was calculated as follows: ...
Plants are exposed to various environmental stresses. To mechano-stimulation, such as wind and touch, leaves immediately respond by bending and twisting or acclimate over a longer time period by thigmomorphogenetic changes of mechanical and geometrical properties. We selected the peltate leaves of Pilea peperomioides for a comparative analysis of mechano-induced effects on morphology, anatomy and biomechanics of petiole and transition zone. The plants were cultivated for six weeks in a phytochamber divided into four treatment groups: control (no stimulus), touch stimulus (brushing every 30 s), wind stimulus (constant air flow of 4.6 ms -1), and a combination of touch and wind stimuli. Comparing the treatment groups, neither the petiole nor the transition zone show significant thigmomorphogenetic acclimations. However, comparing the petiole and the transition zone, the elastic modulus (E), the torsional modulus (G), the E/G ratio and the axial rigidity (EA) differed significantly, whereas no significant difference was found for the torsional rigidity (GK). The twist-to-bend ratios (EI/GK) of all petioles ranged between 4.33 and 5.99, and of all transition zones between 0.67 and 0.78. Based on the twist-to-bend ratios, we hypothesise that bending loads are accommodated by the petiole, while torsional loads are shared between the transition zone and petiole.
... The tapering mode α is a dimensionless parameter that describes the shape of a slender structure (Figure 2), which is, in our case, the petiole. Calculations of the tapering mode were based on the formulae published by Caliaro et al. (2013). First, we calculated the equivalent radius to account for non-perfectly circular cross-sections: ...
... We calculated the torsional rigidity GK by using the torsion constant K, which is valid for crosssections of any geometry, unlike the polar second moment of area J, which is valid only for circular cross-sections. Based on Equations (9) and (10) and the approach of Caliaro et al. (2013), we calculated the elastic modulus E and torsional modulus G taking into consideration the tapering mode: ...
... However, in formula (19), the tapering mode α is not taken into account. Since we found tapered petioles in all the species studied, the tapering mode α was included in the flexural rigidity EI, similar to the approach given by Caliaro et al. (2013) for the elastic modulus E in Equation (11). The first term is the conventional equation for calculating the elastic modulus in twopoint bending tests, with the assumption of a constant axial second moment of area I. ...
From a mechanical viewpoint, petioles of foliage leaves are subject to contradictory mechanical requirements. High flexural rigidity guarantees support of the lamina and low torsional rigidity ensures streamlining of the leaves in wind. This mechanical trade-off between flexural and torsional rigidity is described by the twist-to-bend ratio. The safety factor describes the maximum load capacity. We selected four herbaceous species with different body plans (monocotyledonous, dicotyledonous) and spatial configurations of petiole and lamina (2-dimensional, 3-dimensional) and carried out morphological-anatomical studies, two-point bending tests and torsional tests on the petioles to analyze the influence of geometry, size and shape on their twist-to-bend ratio and safety factor. The monocotyledons studied had significantly higher twist-to-bend ratios (23.7 and 39.2) than the dicotyledons (11.5 and 13.3). High twist-to-bend ratios can be geometry-based, which is true for the U-profile of Hosta x tardiana with a ratio of axial second moment of area to torsion constant of over 1.0. High twist-to-bend ratios can also be material-based, as found for the petioles of Caladium bicolor with a ratio of bending elastic modulus and torsional modulus of 64. The safety factors range between 1.7 and 2.9, meaning that each petiole can support about double to triple the leaf’s weight.
... The percentage values inherent to the fibre reinforcements are computed with respect to the optimal number of fibre strands. namely, *49 sclerenchyma strands and **24 collenchyma strands (see Figs. 4,5). This because, as the distance between the fibre strands becomes smaller, the gradient of φ between two fibre strands is increased and, therefore, the value of φ in the inner part of the cross-section is raised. ...
... Together, they form a doubly secured mechanical system that is sensitive to drought stress. The decrease of flexural rigidity and, thus, the wilting of the leaf stalk are the result of a turgor-loss-induced decrease of the elastic moduli of both the collenchyma fibres and the parenchyma cells 5 . As a withered leaf stalk cannot be restored to its healthy positioning, even with sufficient water support, the evolution of a redundant mechanical system to maintain the flexural rigidity of the plant, in particular, is of great advantage for selection. ...
During biological evolution, plants have developed a wide variety of body plans and concepts that enable them to adapt to changing environmental conditions. The trade-off between flexural and torsional rigidity is an important example of sometimes conflicting mechanical requirements, the adaptation to which can be quantified by the dimensionless twist-to-bend ratio. Our study considers the triangular flower stalk of Carex pendula , which shows the highest twist-to-bend ratios ever measured for herbaceous plant axes. For an in-depth understanding of this peak value, we have developed geometric models reflecting the 2D setting of triangular cross-sections comprised of a parenchymatous matrix with vascular bundles surrounded by an epidermis. We analysed the mathematical models (using finite elements) to measure the effect of either reinforcements of the epidermal tissue or fibre reinforcements such as collenchyma and sclerenchyma on the twist-to-bend ratio. The change from an epidermis to a covering tissue of corky periderm increases both the flexural and the torsional rigidity and decreases the twist-to-bend ratio. Furthermore, additional individual fibre reinforcement strands located in the periphery of the cross-section and embedded in a parenchymatous ground tissue lead to a strong increase of the flexural and a weaker increase of the torsional rigidity and thus resulted in a marked increase of the twist-to-bend ratio. Within the developed model, a reinforcement by 49 sclerenchyma fibre strands or 24 collenchyma fibre strands is optimal in order to achieve high twist-to-bend ratios. Dependent on the mechanical quality of the fibres, the twist-to-bend ratio of collenchyma-reinforced axes is noticeably smaller, with collenchyma having an elastic modulus that is approximately 20 times smaller than that of sclerenchyma. Based on our mathematical models, we can thus draw conclusions regarding the influence of mechanical requirements on the development of plant axis geometry, in particular the placement of reinforcements.
