Trap Closure Research Articles

Biomechanics on Ultra-Sensitivity of Venus Flytrap's Micronewton Trigger Hairs.

Numerous plants evolve ingeniously microcantilever-based hairs to ultra-sensitively detect out-of-plane quasi-static tactile loads, providing a natural blueprint for upgrading the industrial static mode microcantilever sensors, but how do the biological sensory hairs work mechanically? Here, the action potential-producing trigger hairs of carnivorous Venus flytraps (Dionaea muscipula) are investigated in detail from biomechanical perspective. Under tiny mechanical stimulation, the deformable trigger hair, composed of distal stiff lever and proximal flexible podium, will lead to rapid trap closure and prey capture. The multiple features determining the sensitivity such as conical morphology, multi-scale functional structures, kidney-shaped sensory cells, and combined deformation under tiny mechanical stimulation are comprehensively researched. Based on materials mechanics, finite element simulation, and bio-inspired original artificial sensors, it is verified that the omnidirectional ultra-sensitivity of trigger hair is attributed to the stiff-flexible coupling of material, the double stress concentration, the circular distribution of sensory cells, and the positive local buckling. Also, the balance strategy of slender hair between sensitivity and structural stability (i.e., avoiding disastrous collapse) is detailed revealed. The unique basic biomechanical mechanism underlying trigger hairs is essential for significantly enhancing the performance of the traditional industrial static mode microcantilever sensors, and ensure the stability of arbitrary load perception.

Control of oil and gas formation in the Shahejie Formation by the Li Xian Slope Fracture in the Jizhong Depression

Combining the information on the period of fault activity, hydrocarbon source rock distribution and reservoir distribution within the Lixian slope of the Jizhong Depression, the study was conducted on the controlling role of fractures on hydrocarbon formation. The results of the study show that: 1. the influence of fractures on the formation of traps, (1) the nose-like tectonic zone controls the formation of lithological traps of broken nose traps; (2) traps are formed at the segmentation point of the lower plate of the positive fault Gao Yang fault, which is located at the boundary of the external and external zones; (3) Fault activity controls the formation of trap closure; 2. The influence of fracture on oil and gas transportation, the role of oil and gas in the process of vertical transportation, combined with the location of hydrocarbon source rock development and the activity of the fault, fracture controls the vertical transportation of oil and gas.

DYSCALCULIA, a Venus flytrap mutant without the ability to count action potentials

The Venus flytrap Dionaea muscipula estimates prey nutrient content by counting trigger hair contacts initiating action potentials (APs) and calcium waves traveling all over the trap.1,2,3 A first AP is associated with a subcritical rise in cytosolic calcium concentration, but when the second AP arrives in time, calcium levels pass the threshold required for fast trap closure. Consequently, memory function and decision-making are timed via a calcium clock.3,4 For higher numbers of APs elicited by the struggling prey, the Ca2+ clock connects to the networks governed by the touch hormone jasmonic acid (JA), which initiates slow, hermetic trap sealing and mining of the animal food stock.5 Two distinct phases of trap closure can be distinguished within Dionaea's hunting cycle: (1) very fast trap snapping requiring two APs and crossing of a critical cytosolic Ca2+ level and (2) JA-dependent slow trap sealing and prey processing induced by more than five APs. The Dionaea mutant DYSC is still able to fire touch-induced APs but does not snap close its traps and fails to enter the hunting cycle after prolonged mechanostimulation. Transcriptomic analyses revealed that upon trigger hair touch/AP stimulation, activation of calcium signaling is largely suppressed in DYSC traps. The observation that external JA application restored hunting cycle progression together with the DYSC phenotype and its transcriptional landscape indicates that DYSC cannot properly read, count, and decode touch/AP-induced calcium signals that are key in prey capture and processing.

Frequency of trap closure and capture of prey by Dionaea muscipula in the field

Measurements in the field on dry days indicate that when the traps of Dionaea muscipula (Venus’ flytraps) close, they capture prey about 40% of the time at one site and 44% at another. The 60% and 56% of traps that close but do not catch prey reach their maximum closure on average in about 10 minutes, begin reopening in about 7 hours and completely reopen in 22 hours. Traps that have captured prey tighten along their rims, sealing the lobes and forcing the margins outward into a “narrowed” condition that takes 4 to 6 hours to achieve. Reopening of narrowed traps begins, on average, after 9.2 days and they are fully open in 12.8 days. A few traps that capture large prey never reopen. In dry weather closure frequency of traps capable of closure was low, averaging 3.5%/day at one site and 3.1%/day at another. At both sites the capture frequency of traps capable of closing was only 1.4%/day. The low frequency of capture, and high percentage of closures that result in capture, indicate that the low capture frequency is due to a low number potential prey entering and triggering the trap rather than a low efficiency of capturing the prey that enters. Traps that close, but fail to capture prey, have been observed to be triggered by insects, spiders, snails, and even toads that were far too large to be captured. A few captured beetles have been observed to force their way out of trap lobes. Dionaea traps capture prey at all hours of the day. The capture frequencies are variable and are not significantly higher in any specific time period. Both nocturnal and diurnal animals were captured.

Kinematics Governing Mechanotransduction in the Sensory Hair of the Venus flytrap.

Insects fall prey to the Venus flytrap (Dionaea muscipula) when they touch the sensory hairs located on the flytrap lobes, causing sudden trap closure. The mechanical stimulus imparted by the touch produces an electrical response in the sensory cells of the trigger hair. These cells are found in a constriction near the hair base, where a notch appears around the hair’s periphery. There are mechanosensitive ion channels (MSCs) in the sensory cells that open due to a change in membrane tension; however, the kinematics behind this process is unclear. In this study, we investigate how the stimulus acts on the sensory cells by building a multi-scale hair model, using morphometric data obtained from -CT scans. We simulated a single-touch stimulus and evaluated the resulting cell wall stretch. Interestingly, the model showed that high stretch values are diverted away from the notch periphery and, instead, localized in the interior regions of the cell wall. We repeated our simulations for different cell shape variants to elucidate how the morphology influences the location of these high-stretch regions. Our results suggest that there is likely a higher mechanotransduction activity in these ’hotspots’, which may provide new insights into the arrangement and functioning of MSCs in the flytrap.Dataset: 10.3929/ethz-b-000448954

The Venus flytrap trigger hair-specific potassium channel KDM1 can reestablish the K+ gradient required for hapto-electric signaling.

The carnivorous plant Dionaea muscipula harbors multicellular trigger hairs designed to sense mechanical stimuli upon contact with animal prey. At the base of the trigger hair, mechanosensation is transduced into an all-or-nothing action potential (AP) that spreads all over the trap, ultimately leading to trap closure and prey capture. To reveal the molecular basis for the unique functional repertoire of this mechanoresponsive plant structure, we determined the transcriptome of D. muscipula’s trigger hair. Among the genes that were found to be highly specific to the trigger hair, the Shaker-type channel KDM1 was electrophysiologically characterized as a hyperpolarization- and acid-activated K+-selective channel, thus allowing the reuptake of K+ ions into the trigger hair’s sensory cells during the hyperpolarization phase of the AP. During trap development, the increased electrical excitability of the trigger hair is associated with the transcriptional induction of KDM1. Conversely, when KDM1 is blocked by Cs+ in adult traps, the initiation of APs in response to trigger hair deflection is reduced, and trap closure is suppressed. KDM1 thus plays a dominant role in K+ homeostasis in the context of AP and turgor formation underlying the mechanosensation of trigger hair cells and thus D. muscipula’s hapto-electric signaling.

Calcium dynamics during trap closure visualized in transgenic Venus flytrap.

The leaves of the carnivorous plant Venus flytrap, Dionaea muscipula (Dionaea) close rapidly to capture insect prey. The closure response usually requires two successive mechanical stimuli to sensory hairs on the leaf blade within approximately 30 s (refs. 1-4). An unknown biological system in Dionaea is thought to memorize the first stimulus and transduce the signal from the sensory hair to the leaf blade2. Here, we link signal memory to calcium dynamics using transgenic Dionaea expressing a Ca2+ sensor. Stimulation of a sensory hair caused an increase in cytosolic Ca2+ concentration ([Ca2+]cyt) starting in the sensory hair and spreading to the leaf blade. A second stimulus increased [Ca2+]cyt to an even higher level, meeting a threshold that is correlated to the leaf blade closure. Because [Ca2+]cyt gradually decreased after the first stimulus, the [Ca2+]cyt increase induced by the second stimulus was insufficient to meet the putative threshold for movement after about 30 s. The Ca2+ wave triggered by mechanical stimulation moved an order of magnitude faster than that induced by wounding in petioles of Arabidopsis thaliana5 and Dionaea. The capacity for rapid movement has evolved repeatedly in flowering plants. This study opens a path to investigate the role of Ca2+ in plant movement mechanisms and their evolution.

Functional-morphological analyses of the delicate snap-traps of the aquatic carnivorous waterwheel plant (Aldrovanda vesiculosa) with 2D and 3D imaging techniques.

The endangered aquatic carnivorous waterwheel plant (Aldrovanda vesiculosa) catches prey with 3-5-mm-long underwater snap-traps. Trapping lasts 10-20 ms, which is 10-fold faster than in its famous sister, the terrestrial Venus flytrap (Dionaea muscipula). After successful capture, the trap narrows further and forms a 'stomach' for the digestion of prey, the so-called 'sickle-shaped cavity'. To date, knowledge is very scarce regarding the deformation process during narrowing and consequent functional morphology of the trap. We performed comparative analyses of virtual 3D histology using computed tomography (CT) and conventional 2D histology. For 3D histology we established a contrasting agent-based preparation protocol tailored for delicate underwater plant tissues. Our analyses reveal new structural insights into the adaptive architecture of the complex A. vesiculosa snap-trap. In particular, we discuss in detail the arrangement of sensitive trigger hairs inside the trap and present actual 3D representations of traps with prey. In addition, we provide trap volume calculations at different narrowing stages. Furthermore, the motile zone close to the trap midrib, which is thought to promote not only the fast trap closure by hydraulics but also the subsequent trap narrowing and trap reopening, is described and discussed for the first time in its entirety. Our research contributes to the understanding of a complex, fast and reversible underwater plant movement and supplements preparation protocols for CT analyses of other non-lignified and sensitive plant structures.

A single touch can provide sufficient mechanical stimulation to trigger Venus flytrap closure.

The carnivorous Venus flytrap catches prey by an ingenious snapping mechanism. Based on work over nearly 200 years, it has become generally accepted that two touches of the trap's sensory hairs within 30 s, each one generating an action potential, are required to trigger closure of the trap. We developed an electromechanical model, which, however, suggests that under certain circumstances one touch is sufficient to generate two action potentials. Using a force-sensing microrobotic system, we precisely quantified the sensory-hair deflection parameters necessary to trigger trap closure and correlated them with the elicited action potentials in vivo. Our results confirm the model's predictions, suggesting that the Venus flytrap may be adapted to a wider range of prey movements than previously assumed.

Prey capture analyses in the carnivorous aquatic waterwheel plant (Aldrovanda vesiculosa L., Droseraceae)

We investigated the predator-prey interactions between an Australian ecotype of the carnivorous waterwheel plant (Aldrovanda vesiculosa, Droseraceae) and its potential natural prey, the water flea Daphnia longicephala (Daphniidae), which also occurs in Australia. A. vesiculosa develops snap-traps, which close within ~10–100 ms after mechanical triggering by zooplankton prey. Prey capture attempts (PCAs) were recorded via high-speed cinematography in the laboratory. From 14 recorded PCAs, nine were successful for the plant (the prey was caught), and five were unsuccessful (prey could escape), resulting in a capture rate of ~64%. The prey animals’ locomotion behaviour (antenna beat frequency and movement type) in trap vicinity or inside the open traps is very variable. Traps were mainly triggered with the second antennae. During trap closure, the animals moved only very little actively. A flight response in reaction to an initiated trap closure was not observed. However, several animals could escape, either by having a “lucky” starting position already outside the triggered trap, by freeing themselves after trap closure, or by being pressed out by the closing trap lobes. According to our observations in the successful PCAs, we hypothesize that the convex curvature of the two trap lobes (as seen from the outside) and the infolded trap rims are structural means supporting the capture and retention of prey. Our results are discussed in a broader biological context and promising aspects for future studies are proposed.

Dionaea traps selectively allow small animals to escape

Dionaea muscipula selectively allows small animals to escape using a system of interlocking features that complement each other very efficiently. Ants of the species Lasius neglectus (length 3.5 mm) ran through open traps, pausing on the alluring glands along the rim of the trap moving their mouthparts over them. Analysis of videos revealed the ants primarily passed along the trap rim, over the alluring glands, but sometimes ran down to the leaf base through the trigger hairs occasionally brushing by a hair without triggering the trap, because they did not deliver the two stimuli needed to trigger trap closure. Traps observed for four weeks were estimated from sampled observations to have had a total of about 15,000 trap visits by ants during this time period. Six ants were captured during four weeks indicating a risk of capture of about 0.04%. During this same period ten prey other than ants were captured. Visits for prey other than ants was mostly nocturnal and so low that no visits were observed during the observation period. Compared with the large number of ant visits all other prey visits were orders of magnitude fewer. The selective system that allows small animals to escape includes: 1) Attraction of the ants away from the trigger hairs by alluring glands. 2) Clear visibility of the trigger hairs to a 3.5 mm ant. 3) The requirement of two stimuli for triggering trap closure. 4) The escape allowed for small animals by openings between the marginal bristles during the slower phase of trap closure that follows the rapid snap of the trap. Since ants are known to compose about one third of the captures by Dionaea in its native habitat, selection against the capture of small ants not worth the energy expenditure by the plant is an adaptive mechanism.

Photosynthetic cyclic electron transport provides ATP for homeostasis during trap closure in Dionaea muscipula.

The processes connected with prey capture and the early consumption of prey by carnivorous Dionaea muscipula require high amounts of energy. The aim of the present study was to identify processes involved in flytrap energy provision and ATP homeostasis under these conditions. We determined photosynthetic CO2 uptake and chlorophyll fluorescence as well as the dynamics of ATP contents in the snap traps upon closure with and without prey. The results indicate that upon prey capture, a transient switch from linear to cyclic electron transport mediates a support of ATP homeostasis. Beyond 4 h after prey capture, prey resources contribute to the traps' ATP pool and, 24 h after prey capture, export of prey-derived resources to other plant organs may become preferential and causes a decline in ATP contents. Apparently, the energy demand of the flytrap for prey digestion and nutrient mining builds on both internal and prey-derived resources.

Taste for protein: Chemical signal from prey stimulates enzyme secretion through jasmonate signalling in the carnivorous plant Venus flytrap

Hunting cycle of the carnivorous plant Venus flytrap (Dionaea muscipula Ellis) is comprised of mechanism for rapid trap closure followed by slow hermetical sealing and activation of gene expression responsible for digestion of prey and nutrient uptake. In the present study, we focus on the late phase of Venus's flytrap hunting cycle when mechanical stimulation of the prey ceases and is replaced by chemical cues. We used two nitrogen-rich compounds (chitin and protein) in addition to mechanostimulation to investigate the electrical and jasmonate signalling responsible for induction of enzyme activities. Chemical stimulation by BSA protein and chitin did not induce any additional spontaneous action potentials (APs). However, chemical stimulation by protein induced the highest levels of jasmonic acid (JA) and its isoleucine conjugate (JA-Ile) as well as the expression of studied gene encoding a cysteine protease (dionain). Although chitin is probably the first chemical agent which is in direct contact with digestive glands, presence of protein in the secured trap mimics the presence of insect prey best.

Eye region surface temperature dynamics during acute stress relate to baseline glucocorticoids independently of environmental conditions

Reactions to acute stressors are critical for survival. Yet, the challenges of assessing underlying physiological processes in the field limit our understanding of how variation in the acute stress response relates to fitness in free-living animals. Glucocorticoid secretion during acute stress can be measured from blood plasma concentrations, but each blood sample can only provide information for one point in time. Also, the number of samples that can be extracted from an individual in the field is usually limited to avoid compromising welfare. This restricts capacity for repeated assessment, and therefore temporal resolution of findings within- and between-acute stress responses - both of which are important for determining links between acute stress and fitness. Acute stress induces additional body surface temperature changes that can be measured non-invasively, and at high frequencies using thermal imaging, offering opportunities to overcome these limitations. But, this method's usefulness in the field depends on the extent that environmental conditions affect the body surface temperature response, which remains poorly understood. We assessed the relative importance of individual physiology (baseline glucocorticoid concentrations) and environmental conditions (air temperature and relative humidity) in determining the eye region surface temperature (Teye) response to acute stress, in wild blue tits (Cyanistes caeruleus) during trapping, handling and blood sampling. When controlling for between-individual baseline variation, Teye initially dropped rapidly below, and then recovered above baseline, before declining more slowly until the end of the test, 160 s after trap closure. One measure of the amplitude of this response – the size of the initial drop in Teye – was dependent on environmental conditions, but not baseline corticosterone. Whereas, two properties defining response dynamics – the timing of the initial drop, and the slope of the subsequent recovery – were related to baseline corticosterone concentrations, independently of environmental conditions. This suggests inferring the acute stress response using thermal imaging of Teye will be practical under fluctuating environmental conditions in the field.

Excitation and emission wavelength dependence of fluorescence spectra in whole cells of the cyanobacterium Synechocystis sp. PPC6803: Influence on the estimation of Photosystem II maximal quantum efficiency

The fluorescence emission spectrum of Synechocystis sp. PPC6803 cells, at room temperature, displays: i) significant bandshape variations when collected under open (F0) and closed (FM) Photosystem II reaction centre conditions; ii) a marked dependence on the excitation wavelength both under F0 and FM conditions, due to the enhancement of phycobilisomes (PBS) emission upon their direct excitation. As a consequence: iii) the ratio of the variable and maximal fluorescence (FV/FM), that is a commonly employed indicator of the maximal photochemical quantum efficiency of PSII (Φpc, PSII), displays a significant dependency on both the excitation and the emission (detection) wavelength; iv) the FV/FM excitation/emission wavelength dependency is due, primarily, to the overlap of PSII emission with that of supercomplexes showing negligible changes in quantum yield upon trap closure, i.e. PSI and a PBS fraction which is incapable to transfer the excitation energy efficiently to core complexes. v) The contribution to the cellular emission and the relative absorption-cross section of PSII, PSI and uncoupled PBS are extracted using a spectral decomposition strategy. It is concluded that vi) Φpc, PSII is generally underestimated from the FV/FM measurements in this organism and, the degree of the estimation bias, which can exceed 50%, depends on the measurement conditions. Spectral modelling based on the decomposed emission/cross-section profiles were extended to other processes typically monitored from steady-state fluorescence measurements, in the presence of an actinic illumination, in particular non-photochemical quenching. It is suggested that vii) the quenching extent is generally underestimated in analogy to FV/FM but that viii) the location of quenching sites can be discriminated based on the combined excitation/emission spectral analysis.

Curvature-Induced Instabilities of Shells.

Induced by proteins within the cell membrane or by differential growth, heating, or swelling, spontaneous curvatures can drastically affect the morphology of thin bodies and induce mechanical instabilities. Yet, the interaction of spontaneous curvature and geometric frustration in curved shells remains poorly understood. Via a combination of precision experiments on elastomeric spherical shells, simulations, and theory, we show how a spontaneous curvature induces a rotational symmetry-breaking buckling as well as a snapping instability reminiscent of the Venus fly trap closure mechanism. The instabilities, and their dependence on geometry, are rationalized by reducing the spontaneous curvature to an effective mechanical load. This formulation reveals a combined pressurelike term in the bulk and a torquelike term in the boundary, allowing scaling predictions for the instabilities that are in excellent agreement with experiments and simulations. Moreover, the effective pressure analogy suggests a curvature-induced subcritical buckling in closed shells. We determine the critical buckling curvature via a linear stability analysis that accounts for the combination of residual membrane and bending stresses. The prominent role of geometry in our findings suggests the applicability of the results over a wide range of scales.

Venus Flytrap: How an Excitable, Carnivorous Plant Works.

The carnivorous plant Dionaea possesses very sensitive mechanoreceptors. Upon contact with prey an action potential is triggered which, via an electrical network - comparable to the nervous system of vertebrates - rapidly closes its bivalved trap. The 'hunting cycle' comprises a constitutively activated mechanism for the rapid capture of prey, followed by a well-orchestrated sequence of activation of genes responsible for tight trap closure, digestion of the prey, and uptake of nutrients. Decisions on the step-by-step activation are based on 'counting' the number of stimulations of sensory organs. These remarkable animal-like skills in the carnivore are achieved not by taking over genes from its prey but by modifying and rearranging the functions of genes that are ubiquitous in plants.

Spontaneous action potentials and circumnutation in Helianthus annuus

Action potentials (APs) in plants are involved in fast leaf or trap closure as well as elongation, respiration, photosynthesis, and fertilization regulation. Here, spontaneous APs (SAPs) in relation to endogenous stem movement named circumnutation (CN) have been investigated in Helianthus annuus in different light conditions in freely circumnutating and immobilized plants. Extracellular electrical measurements and time-lapse photography were carried out simultaneously. The parameters of CN (trajectory length, period, and direction) and the number and transmission direction of SAPs were analysed. In continuous light (25–40 μmol m−2 s−1), all plants circumnutating vigorously in a regular elliptical manner and no SAPs were observed. In light/dark conditions, the plants circumnutated in a daily pattern, most SAPs were observed in the dark and freely circumnutated sunflowers had two times more SAPs (10 SAPs/24 h/plant) than the immobilized plants (5 SAPs/24 h/plant). In continuous very low light (5 μmol m−2 s−1), the plants circumnutated weakly and irregularly and SAPs appeared without the circadian pattern. 3–5 SAPs/24/plant occurred in the freely circumnutating and immobilized plants. In light/dark and continuous very low light conditions, an ultradian rhythm of SAPs was observed and the mean spacing between SAPs was approx. 121–271 min in the freely circumnutating and immobilized plants. Under all light conditions, more SAPs were transmitted basipetally than acropetally. One-hour lasting series of 3–4 min spaced SAPs locally propagated were observed as well in very low light. Basipetal and acropetal SAPs passing along the stem motor region accompany irregularity, changes in the CN trajectory direction, and stem torsion. These results demonstrate that APs and CN changes play a role in plant adaptation to light conditions and that there is an ultradian rhythm of SAPs beside ultradian CN rhythm.

Triggering a false alarm: wounding mimics prey capture in the carnivorous Venus flytrap (Dionaea muscipula).

In the carnivorous plant Venus flytrap (Dionaea muscipula), the sequence of events after prey capture resembles the well-known plant defence signalling pathway in response to pathogen or herbivore attack. Here, we used wounding to mimic prey capture to show the similarities and differences between botanical carnivory and plant defence mechanisms. We monitored movement, electrical signalling, jasmonate accumulation and digestive enzyme secretion in local and distal (systemic) traps in response to prey capture, the mechanical stimulation of trigger hairs and wounding. The Venus flytrap cannot discriminate between wounding and mechanical trigger hair stimulation. Both induced the same action potentials, rapid trap closure, hermetic trap sealing, the accumulation of jasmonic acid (JA) and its isoleucine conjugate (JA-Ile), and the secretion of proteases (aspartic and cysteine proteases), phosphatases and type I chitinase. The jasmonate accumulation and enzyme secretion were confined to the local traps, to which the stimulus was applied, which correlates with the propagation of electrical signals and the absence of a systemic response in the Venus flytrap. In contrast to plant defence mechanisms, the absence of a systemic response in carnivorous plant may represent a resource-saving strategy. During prey capture, it could be quite expensive to produce digestive enzymes in the traps on the plant without prey.

Resting electrical network activity in traps of the aquatic carnivorous plants of the genera Aldrovanda and Utricularia.

In this study the MEA (multielectrode array) system was used to record electrical responses of intact and halved traps, and other trap-free tissues of two aquatic carnivorous plants, Aldrovanda vesiculosa and Utricularia reflexa. They exhibit rapid trap movements and their traps contain numerous glands. Spontaneous generation of spikes with quite uniform shape, propagating across the recording area, has been observed for all types of sample. In the analysis of the electrical network, higher richer synchronous activity was observed relative to other plant species and organs previously described in the literature: indeed, the time intervals between the synchronized clusters (the inter-spike intervals) create organized patterns and the propagation times vary non-linearly with the distance due to this synchronization. Interestingly, more complex electrical activity was found in traps than in trap-free organs, supporting the hypothesis that the nature of the electrical activity may reflect the anatomical and functional complexity of different organs. Finally, the electrical activity of functionally different traps of Aldrovanda (snapping traps) and Utricularia (suction traps) was compared and some differences in the features of signal propagation were found. According to these results, a possible use of the MEA system for the study of different trap closure mechanisms is proposed.