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Mimosa pudica rapidly folds leaves when touched. Motion is created by pulvini, ‘the plant muscles’ that allow plants to produce various complex motions. Plants rely on local control of the turgor pressure to create on-demand motion. In this paper, the mechanics of a cellular material inspired from pulvinus of M. pudica is studied. First, the manufacturing process of a cell-controllable material is described. Its deformation behaviour when pressured is tested, focusing on three pressure patterns of reference. The deformations are modelled based on the minimisation of elastic energy framework. Depending on pressurisation pattern and magnitude, reversible buckling-induced motion may occur.

Mechanoperception, the ability to perceive and respond to mechanical stimuli, is a common and fundamental property of all forms of life. Vascular plants such as Mimosa pudica use this function to protect themselves against herbivory. The mechanical stimulus caused by a landing insect triggers a rapid closing of the leaflets that drives the potential pest away. While this thigmonastic movement is caused by ion fluxes accompanied by a rapid change of volume in the pulvini, the mechanism responsible for the detection of the mechanical stimulus remains poorly understood. Here, we examined the role of mechanosensitive ion channels in the first step of this evolutionarily conserved defense mechanism: the mechanically evoked closing of the leaflet. Our results demonstrate that the key site of mechanosensation in the Mimosa leaflets is the pulvinule, which expresses a stretch-activated chloride-permeable mechanosensitive ion channel. Blocking these channels partially prevents the closure of the leaflets following mechanical stimulation. These results demonstrate a direct relation between the activity of mechanosensitive ion channels and a central defense mechanism of M. pudica., One-sentence summary: Vascular plants use mechanosensitive ion channels to move their leaflets in response to external mechanical stimuli.

International audience; Tryptophan at concentrations higher than 0.1 mM, triggered characteristic early physiological effects such as rapid (within 5 min) dose-dependent membrane hyperpolarization in Mimosa pudica motor cells and modification of the time course of the spontaneous proton efflux monitored in the incubation medium of pulvinar tissues. The rapid modifications of the leaf turgor-mediated movements seen on the primary pulvini of M. pudica following a shock and on Cassia fasciculata leaflets during a transition from light to darkness indicate that tryptophan disturbed the ionic migrations involved in the electrophysiological events and in the osmocontractile reaction of the motor cells. These reactions were specific to tryptophan compared to those induced by serine and 5-hydroxytryptophan. The tryptophan mode of action cannot be linked to a direct modification of the plasma membrane H+-ATPase activity as monitored on purified pulvinar plasma membrane vesicles. The tryptophan metabolism-linked products tryptamine and indole also inhibited the motile reactions, activated in a continuous manner the H+ secretion of pulvinar tissues and showed properties of a protonophore and an ATPase activity inhibitor on plasma membrane vesicles, respectively. The specific behavior of tryptophan in the reaction studies here is discussed in light of the previously reported action of phytohormones.

Two Fabaceae exhibiting rapid osmocontractile pulvinar movements were used in this study because this activity is modified by natural auxin and dramatically by 2,4D. A short chain with a carboxylic group being required for auxinic properties, a critical point to analyze is whether the recently synthesized proherbicide e-(2,4-dichlorophenoxyacetyl)-L-Lys (2-4D-L-Lys) maintains some biological activity despite the increase in length of the chain and the substitution of the carboxyl group by an α-amino acid function. No trace of 2,4D could be detected in the pulvinar tissues treated for 1 h with 2,4D-L-Lys. Complementary approaches (electrophysiology, pH measurements, use of plasma membrane vesicles) suggest that it was less efficient than 2,4D to activate the plasma membrane H+-ATPase (PM-H+-ATPase). However, it modified the various ion-driven reactions of Mimosa pudica and Cassia fasciculata pulvini in a similar way as 2,4D. Additionally, it was much more effective than fusicoccin to inhibit seismonastic movements of M. pudica leaves and, at low concentrations, to promote leaflet opening in dark, indicating that its mode of action is more complex than the only activation of the PM-H+-ATPase. Various substitutions on 2,4D-L-Lys affected its activity in correlation with the molecular descriptor “halogen ratio” of these derivatives. Conjugation with D-Lys also led to a decrease of pulvinar reaction, suggesting that 2,4D-Lys maintains the main signaling properties of 2,4D involved in pulvinar movements providing that the terminal zwitterion is in a suitable orientation. Our data guide future investigations on the effect of 2,4D and 2,4D-L-Lys on the vacuolar pump activity of motor cells.

Potassium pyroantimonate precipitation, transmission electron microscopy, and X-ray microanalysis were used to investigate the subcellular localization of loosely bound calcium in Robinia pseudoacacia pulvinar motor cells during phytochrome-mediated nyctinastic closure. Calcium localization was carried out in pulvini collected in white light 2 h after the beginning of the photoperiod, immediately after a red light or a far-red light pulse applied 2 h after the beginning of the photoperiod and after 15 or 25 min of darkness respectively. Calcium antimonate precipitates were found in all the pulvinar tissues from the epidermis to the vascular bundle, independent of the light treatment. At subcellular level, precipitates were found mainly in the intercellular spaces, the inner surface of the plasma membrane, cytoplasm, colloidal vacuoles, and nuclei. Red light enhanced the nyctinastic closure of leaflets and caused an asymmetric distribution of cytosolic calcium precipitates between the extensor and flexor motor cells. Both the number and area of the cytosolic calcium precipitates drastically increased in the extensor cells compared to the flexor motor cells. Red light had a rapid and transient effect on the distribution of cytosolic calcium precipitates, which occurred during or at the end of the irradiation, before leaflet closure. By contrast, the distribution of cytosolic loosely bound calcium was similar between the extensor and flexor motor cells after irradiation with far-red light. Our results demonstrate that red light causes specific calcium mobilization in pulvinar motor cells and suggest the involvement of cytoplasmic Ca2+ as a second messenger for phytochrome during nyctinastic closure.

A remarkable feature of Mimosa pudica is its ability to deform in response to certain external stimuli. Here, a two-dimensional transient bio-chemo-electro-mechanical model of the rapid movement of the main pulvinus of Mimosa pudica is developed. Based on the laws of mass and momentum conservation, poroelasticity, and representative volume elements, a novel fluid pressure equation is proposed to characterize the cell elasticity. Experiments were conducted to measure the time and amplitude of the rapid movement. After examinations with the published experiments, it is confirmed that the model can predict well the ionic concentrations, petiole bending angle, and membrane potential. The simulation analysis of the biophysical properties provides insights to biomechanics: the hydrostatic pressure in the lowest extensor decreases from 0.35 to 0.05 MPa at t = 0.00 to 3.00 s; fluid pressure increases from 0.00 to 0.11 MPa at t = 0.00 to 0.14 s; and the peak bending angle increases from 57.0° to 70.9° when the reflection coefficient is assigned as 0.10 to 0.20 in the model. The results highlight the biochemical actuation mechanism of the Mimosa pudica movement, and they confirm the importance of ionic and water transports for causing changes in osmotic and hydrostatic pressures. Nanyang Technological University The authors gratefully acknowledge the financial support from Nanyang Technological University through NTU Research Scholarship. The authors thank Mr. Neo De Sheng for the help on data collation.

Current concepts of plant membrane transport are based on the assumption that water and solutes move across membranes via separate pathways. According to this view, coupling between the fluxes is more or less exclusively constituted via the osmotic force that solutes exert on water transport. This view is questioned here, and experimental evidence for a cotransport of water and solutes is reviewed. The overview starts with ion channels that provide pathways for both ion and water transport, as exemplified for maxi K+ channels from cytoplasmic droplets of Chara corallina. Aquaporins are usually considered to be selective for water (just allowing for slippage of some other small, neutral molecules). Recently, however, a “dual function” aquaporin has been characterized from Arabidopsis thaliana (AtPIP2.1) that translocates water and at the same time conducts cations, preferentially Na+. By analogy with mammalian physiology, other candidates for solute-water flux coupling are cation-chloride cotransporters of the CCC type, and transporters of sugars and amino acids. The last part is dedicated to possible physiological functions that could rely on solute-water cotransport. Among these are the generation of root pressure, refilling of embolized xylem vessels, fast turgor-driven movements of leaves, cell elongation (growth), osmoregulation and adjustment of buoyancy in marine algae. This review will hopefully initiate further research in the field.

The orientation of plant organs perpendicular to the plain of the sun’s rays, which is called ortho- or dia-heliotropism, maximizes light absorbance, whereas the orientation parallel to the sun’s rays, which is called para-heliotropism, minimizes light absorbance. Heliotropic movements occur by asymmetric volume changes at both sides of the moving organ via reversible turgor-mediated alterations in the pulvinus shape or cell elongation. The pulvinus found at the base of the leaf or the leaflet petiole is a vascular tissue surrounded by a cylinder-like cortex of thin-walled elastic parenchyma cells. The daily alterations in sun position and light intensity and on the other hand the absolute dependence of plants on light led to the evolution of heliotropic responses in plants to optimize sunlight utilization under unfavorable conditions. Heliotropic movements also occur in plants and organs lacking pulvini by a differential and irreversible cell growth on two opposite sides of the organ or Anemone rivularis..

In grapevine, climate changes lead to increased berry potassium (K+ ) contents that result in must with low acidity. Consequently, wines are becoming 'flat' to the taste, with poor organoleptic properties and low potential aging, resulting in significant economic loss. Precise investigation into the molecular determinants controlling berry K+ accumulation during its development are only now emerging. Here, we report functional characterization by electrophysiology of a new grapevine Shaker-type K+ channel, VvK3.1. The analysis of VvK3.1 expression patterns was performed by qPCR and in situ hybridization. We found that VvK3.1 belongs to the AKT2 channel phylogenetic branch and is a weakly rectifying channel, mediating both inward and outward K+ currents. We showed that VvK3.1 is highly expressed in the phloem and in a unique structure located at the two ends of the petiole, identified as a pulvinus. From the onset of fruit ripening, all data support the role of the VvK3.1 channel in the massive K+ fluxes from the phloem cell cytosol to the berry apoplast during berry K+ loading. Moreover, the high amount of VvK3.1 transcripts detected in the pulvinus strongly suggests a role for this Shaker in the swelling and shrinking of motor cells involved in paraheliotropic leaf movements.

There is an amazing array of leaf movements among plants, elicited by a wide variety of environmental signals. Leaf movements may occur over developmental time scales, involving growth processes, or over the scale of milliseconds involving rapid depolarization of membranes and ion fluxes. This chapter covers primarily leaf movements in response to light, although mechanical stimuli, temperature, and water are also discussed. The focus on phototropism, heliotropism, and thermonasty is due to the large effects these movements have on rates of photosynthesis. Heliotropism, whether it is due to differential growth on opposite sides of a plant stem, or turgor changes within a motor organ such as a pulvinus, has direct and large effects on light interception. Diaheliotropic, paraheliotropic, or a combination of the two movements may act to increase photosynthesis by increasing light interception, or optimize resource use efficiency by modulating incident light at intermediate levels. Paraheliotropic and wilting movements are major adaptive mechanisms in response to water deficits, high light, high temperatures, or a combination of these stresses. Thermonastic movements have been shown to play a major role in reducing damage to the photosynthetic machinery during low temperature periods, or conversely in high temperature periods. Despite the mounting number of case studies, a comprehensive understanding of the signal cascades and regulatory genetic pathways controlling rapid, reversible leaf movements has yet to be accomplished. An understanding of the phylogeographic distribution of rapid leaf movements is also lacking. The presence of rapid leaf movements in a number of commercially important crop species suggests that incorporation and modification of these properties may have potential to improve both productivity and stress resistance in cultivated species.

Mimosa Pudica (also known as Pokok Semalu) is an action plant with unique biological cell mechanism that has great potential to be explored for next generation biomechatronics devices. The motion principle of each petiole movement occurs by an organ of motion, called pulvinus. The behavior analysis of the Mimosa Pudica plant main pulvinus and petiole against external stimulations has been investigated. The response of the plant cell was observed by optical and scanning electron microscopes (SEM). External stimulation tests on Mimosa Pudica plant such as mechanical, electrical and light stimulations were conducted. Optical microscopy and SEM observations revealed the existence of red cells in the tertiary pulvinus. Mechanical stimulation results had shown a response time of approximately 2 seconds and a recovery time of 10 to 12 minutes for the leaves and 20 minutes for the petiole. Bending force of the petiole of Mimosa Pudica was also measured. The torque generated by the bending of petiole was found to increase exponentially as the pulvinus diameter increased. A torque of 30.91 g mm was generated from the bending of a petiole with 1.5 mm pulvinus diameter. The lifting potential of the Mimosa Pudica was tested using loadings with increments of 0.42 gram. The plant responded to electrical stimulation of 1.3 Ampere and displayed side effect. The light sensitivity region of Mimosa Pudica was obtained through light stimulation using a full spectrum daylight bulb, and ranges from 50 to 300 lux. Signal transmission to neighbouring structures was observed when the leaf was stimulated with threatening stimulus, with the signal speed achieving 0.8 cm/s. Movement mechanism of Mimosa Pudica is believed to be triggered by signal through receptor cells. It was found that the torque generated during petiole lifting is relatively higher than that during petiole bending.

Early prediction of compound absorption by cells is of considerable importance in the building of an integrated scheme describing the impact of a compound on intracellular biological processes. In this scope, we study the structure-activity relationships of several benzoic acid-related phenolics which are involved in many plant biological phenomena (growth, flowering, allelopathy, defense processes). Using the partial least squares (PLS) regression method, the impact of molecular descriptors that have been shown to play an important role concerning the uptake of pharmacologically active compounds by animal cells was analyzed in terms of the modification of membrane potential, variations in proton flux, and inhibition of the osmocontractile reaction of pulvinar cells of Mimosa pudica leaves. The hydrogen bond donors (HBD) and hydrogen bond acceptors (HBA), polar surface area (PSA), halogen ratio (Hal ratio), number of rotatable bonds (FRB), molar volume (MV), molecular weight (MW), and molar refractivity (MR) were considered in addition to two physicochemical properties (logD and the amount of non-dissociated form in relation to pKa). HBD + HBA and PSA predominantly impacted the three biological processes compared to the other descriptors. The coefficient of determination in the quantitative structure-activity relationship (QSAR) models indicated that a major part of the observed seismonasty inhibition and proton flux modification can be explained by the impact of these descriptors, whereas this was not the case for membrane potential variations. These results indicate that the transmembrane transport of the compounds is a predominant component. An increasing number of implicated descriptors as the biological processes become more complex may reflect their impacts on an increasing number of sites in the cell. The determination of the most efficient effectors may lead to a practical use to improve drugs in the control of microbial attacks on plants.

The effect of different spectral ranges of light on the modification of transport processes in isolated parts of Phaseolus coccineus pulvini was analysed in a bath medium by determining the Ca2+ and K+ contents. After 1 h incubation of separated fragments of the extensor and flexor in solutions containing deionized water, medium, or medium with verapamil or nifedipine, the investigated material was irradiated with monochromatic light of different wavelengths. The concentration of Ca2+, K+ and the pH value were determined in the medium. The obtained results suggest the occurrence of a specific coupling between the concentration of Ca2+ and K+ dependend on the wavelength of the applied light and part of the pulvinus. Certain spectral ranges of light brought about opposite effects on ion transport in opposite parts of the pulvinus. Changes in the pH of mediums containing isolated parts of the pulvini part to different effects of blue, red, and far-red light on the activity of H+-pumps located in the motor cells. The use of verapamil and nifedipine, specific Ca2+-channel blockers, made it possible to demonstrate the significant effect of Ca2+ on the activity and functioning of K+ -channels. The two types of inhibitors decreased the influx of Ca2+ and K+ to motor cells of the pulvini, however they did not limit the efflux of ions to the medium. The obtained results suggest that Ca2+ ions take part in transduction of the light signal. It seems probable that the action of blue light is also mediated by part of the Ca2+ ions.

Some plant species both track and avoid the sun through turgor changes of the pulvinus tissue at the base of their leaves, maximizing light reception in dim conditions and minimizing cellular damage due to excessive light. Pulvinar response is known to be affected by both diurnally varying environmental factors and circadian patterns. Differential expression of the proteins between light and darkness are not well-known. In this study we used two-dimensional gel electrophoresis and mass spectrometry to separate and identify proteins in the soybean leaf pulvinus that were differentially expressed in the light compared to a dark control. Out of 165 protein spots previously identified (data not shown) 11 were found to have decreased expression in the light and 7 had increased light expression. The proteins that were more highly expressed in the light were mostly stress response proteins, while the under-expressed proteins were categorized as energy proteins. While the higher levels of expression of stress response proteins in the light align with other studies, the under-expressed light proteins require further examination to rule out artefactual results. These findings can provide a better understanding of the circadian pattern of protein expression in the legume pulvinus proteome.

The bending movement of the pulvinus of Mimosa pudica is caused by a rapid change in volume of the abaxial motor cells, in response to various environmental stimuli. We investigated the relationship between the actin cytoskeleton and changes in the level of calcium during rapid contractile movement of the motor cells that was induced by electrical stimulation. The bending of the pulvinus was retarded by treatments with actin-affecting reagents and calcium channel inhibitors. The actin filaments in the motor cells were fragmented in response to electrical stimulation. Further investigations were performed using protoplasts from the motor cells of M. pudica pulvini. Calcium-channel inhibitors and EGTA had an inhibitory effect on contractile movement of the protoplasts. The level of calcium increased and became concentrated in the tannin vacuole after electrical stimulation. Ruthenium Red inhibited the increase in the level of calcium in the tannin vacuole and the contractile movement of the protoplasts. However, treatment with latrunculin A abolished the inhibitory effect of Ruthenium Red. Phalloidin inhibited the contractile movement and the increase in the level of calcium in the protoplasts. Our study demonstrates that depolymerization of the actin cytoskeleton in pulvinus motor cells in response to electrical signals results in increased levels of calcium.

Special red cells were found on the adaxial surface of tertiary pulvini of Mimosa pudica and experiments performed to determine the origin and function of these cells. Using anatomical (light, scanning electron and transmission electron microscopy) and electrophysiological techniques, we have demonstrated that these red cells are real mechanoreceptor cells. They can generate receptor potential following mechanical stimuli and they are in connection with excitable motor cells (through plasmodesmata). We also provide evidence that these red cells are derived from stomatal subsidiary cells and not guard cells. As histochemical studies show red cells contain tannin, which is important in development of action potentials and movements of plants. These cells could be one of unidentified mechanoreceptors of mimosa.

Rhythmic up-down movements were studied in the lateral leaflets ofDesmodium gyrans (L.F.) DC. These were recorded with a video-computer system, whereby the digital video signals from a CCD camera were processed with special software. Under control conditions (24°C and 0.1 nM cm-2 s-1 of stable, dim light), the average period of lateral leaflet movement was 3.5 min. In the presence of light stimuli (for 2 min), those leaflets always moved toward the light, regardless of where it was applied to any axial part of the pulvinus. The strongest effect was manifested by a reduced amplitude of movement and, thus, a shortened period, which could be up to ~43% less under moderate light intensity (5 nM cm-2 s-2). Oscillations regained their original regularity over ~10 cycles after the light stimulus was removed. In addition, these oscillations temporarily disappeared after long exposure (~10 min) under moderate light, or when the leaflets were quickly exposed to a higher intensity (~12 nM cm-2s-1). Therefore, we have now demonstrated that light can affect physiological parameters that are involved in the control of oscillations.

“Osmotic Motors” – the best-documented explanation for plant leaf movements – frequently reside in specialized motor leaf organs, pulvini. The movements result from dissimilar volume and turgor changes in two oppositely positioned parts of the pulvinus. This Osmotic Motor is powered by a plasma membrane proton ATPase, which drives KCl fluxes and, consequently, water, across the pulvinus into swelling cells and out of shrinking cells. Light signals and signals from the endogenous biological clock converge on the channels through which these fluxes occur. These channels and their regulatory pathways in the pulvinus are the topic of this review.

Heat stress hurts rice, and floral organs are mostly sensitive to heat stress. We aimed to unravel molecular responses to heat stress in rice floral organs using Illumina/Solexa sequencing technology for addressing the increasing concern of globle warming. At meiophase of the pollen mother cell (pulvinus flat), the plants were stressed for 3 d at 38 C, and RNA was extracted from the stressed pistil and stamen for RNA-Seq sequencing to build the heat stress transcriptom library. A total of 7178 defferentially expressed genes (DEGs) between the normal and heat stress libraries were significant, 61% up-regulated and 39% down-regulated. The 7178 DEGs were significantly classified to 34 gene ontology (GO) categories, and 11 of the GO categories were significantly enriched. The GO:0016787 for hydrolase activity of molecular function was mostly enriched with the least probability, and included 11 DEGs named Hy1 - Hy11. Expression levels of five DEGs, Hy4 - Hy6 and Hy9 - Hy10 for starch and sucrose metablism via pectinase, increased 12 - 14 times in response to the heat stress. Further investigation of the five DEGs for pectin metabolism and association with reported heat responsive genes may help develop a molecular strategy to remedy heat damage in rice.

Daily periodic plant leaf movements, known since antiquity, are dramatic manifestations of “osmotic motors” regulated by the endogenous biological clock and by light, perceived by phytochrome and, possibly, by phototropins . Both the reversible movements and their regulation usually occur in specialized motor leaf organs, pulvini. The movements result from opposing volume changes in two oppositely positioned parts of the pulvinus . Water fluxes into the motor cells in the swelling part and out of the motor cells in the concomitantly shrinking part are powered by ion fluxes into and out of these cells, and all of these fluxes occur through tightly regulated membranal proteins: pumps, carriers, and ion and water channels. This chapter attempts to piece together those findings and insights about this mechanism which have accumulated during the past two and a half decades.

This study was conducted to unravel a mechanism for the gravitropic curvature response in oat (Avena sativa) shoot pulvini. For this purpose, we examined the downward movement of starch-filled chloroplast gravisensors, differential changes in inositol 1,4,5-trisphosphate (IP(3)) levels, transport of indole-3-acetic acid (IAA) and gravitropic curvature. Upon gravistimulation, the ratio for IAA levels in lower halves versus those in upper halves (L/U) increased from 1.0 at 0 h and reached a maximum value of 1.45 at 8 h. When shoots were grown in the dark for 10 d, to deplete starch in the chloroplast, the gravity-induced L/U of IAA was reduced to 1.0. N-naphthylphthalamic acid (NPA) and 2,3,5-triiodobenzoic acid (TIBA), both auxin transport inhibitors, significantly reduced the amount of gravitropic curvature and gravity-induced lateral IAA transport, but did not reduce the gravity-induced late change in the L/U ratio of IP(3) levels. U73122, a specific phospholipase C (PLC) inhibitor, decreased gravity-induced curvature. Because U73122 reduced the ratio of L/U of IAA imposed by gravistimulation, it is clear that IAA transport is correlated with changes in IP(3) levels upon gravistimulation. These results indicate that gravistimulation-induced differential lateral IAA transport may result from the onset of graviperception in the chloroplast gravisensors coupled with gravity-induced asymmetric changes in IP(3) levels in oat shoot pulvini.

The maize (Zea mays L.) pulvinus was used as a model system to study the signalling events that lead to differential growth in response to gravistimulation in plants. The pulvinus functions to return tipped plants to vertical via differential elongation of the cells on its lower side. By performing immunokinase assays using total soluble protein extracts and an antibody against mammalian ERK1, a mitogen-activated protein kinase (MAPK)-like activity was assayed in pulvini halves harvested at various time points after tipping. We detected a reproducible alternation of higher levels of activity occurring between the upper and lower halves of the pulvinus between 75 and 180 min after tipping, with a sustained increase in the upper half occurring at the end of the time-course. This timing roughly corresponds to the presentation time for maize (i.e. the amount of time that the plant needs to be tipped before it is committed to bend), which occurs between 2 and 4 h. Treatment of maize stem explants with an inhibitor of MAPK activation, U0126, led to a reduction in the activity of this kinase, as well as an almost 65% reduction in bending as measured at 20 h. Rinsing out of the inhibitor resulted in recovery of both bending and kinase activity. It is possible that changes in MAPK activity in the gravistimulated pulvinus are part of a signalling cascade that may help to distinguish between minor perturbations in plant orientation and more significant and long-term changes, and may also help to determine the direction of bending.

The laminar pulvinus of bean (Phaseolus vulgaris L.) is a highly specialized organ for reorienting the lamina, and exhibits positive phototropic curvature. Structural and ultrastructural features of the pulvinus were studied to determine their possible role in its phototropic response. The vascular tissue forms a flexible, relatively inextensible central core enclosed by a starch sheath and surrounded by a multi-layered motor tissue. Phototropic curvature is a result of opposite anisotropic changes in volume of the cells in the exposed and opposite sectors of the motor tissue. Radial inflexibility of the epidermis and axial plasticity constrain these changes to the pulvinar axis. Anisotropic changes in volume of motor cells reduce the osmotic work involved. Motor cells exhibit features that are associated with high synthetic activity: thick cytoplasm with numerous ribosomes, polysomes, RER and SER, well-developed mitochondria and a large nucleus. Numerous, well-developed chloroplasts, with little starch, are increasingly abundant toward the periphery. The intercellular system is limited and partially filled with matrix. Stomata are absent and the motor tissue lacks vascularization. These features support the suggestion that the primary role of the chloroplasts in the photonastic response is photophosphorylation and photosynthetic electron transport (Koller et al., 1995[339]).

Certain plant species respond to light, dark, and other environmental factors by leaf movement. Leguminous plants both track and avoid the sun through turgor changes of the pulvinus tissue at the base of leaves. Mechanisms leading to pulvinar turgor flux, particularly knowledge of the proteins involved, are not well-known. In this study we used two-dimensional gel electrophoresis and liquid chromatography-tandom mass spectrometry to separate and identify the proteins located in the soybean pulvinus. A total of 183 spots were separated and 195 proteins from 165 spots were identified and functionally analyzed using single enrichment analysis for gene ontology terms. The most significant terms were related to proton transport. Comparison with guard cell proteomes revealed similar significant processes but a greater number of pulvinus proteins are required for comparable analysis. To our knowledge, this is a novel report on the analysis of proteins found in soybean pulvinus. These findings provide a better understanding of the proteins required for turgor change in the pulvinus.

Mimosa pudica is a plant that rapidly shrinks its body in response to external stimuli. M. pudica does not perform merely simple movements, but exhibits a variety of movements that quickly change depending on the type of stimuli. Previous studies have investigated the motile mechanism of the plants from a biochemical perspective. However, an interdisciplinary study on the structural characteristics of M. pudica should be accompanied by biophysical research to explain the principles underlying such movements. In this study, the structural characteristics and seismonastic reactions of M. pudica were experimentally investigated using advanced bio-imaging techniques. The results show that the key factors for the flexible movements by the pulvinus are the following: bendable xylem bundle, expandable/shrinkable epidermis, tiny wrinkles for surface modification and a xylem vessel network for efficient water transport. This study provides new insight for better understanding the M. pudica motile mechanism through structural modification.

The intermittent influx of K+ into motor cells in motor organs (pulvini) is essential to the rhythmic movement of leaves and leaflets in various plants, but in contrast to the K+ influx channels in guard cells, those in pulvinar motor cells have not yet been characterized. We analyzed these channels in the plasma membrane of pulvinar cell protoplasts of the nyctinastic legume Samanea saman using the patch-clamp technique. Inward, hyperpolarization-activated currents were separated into two types: time dependent and instantaneous. These were attributed, respectively, to K+-selective and distinctly voltage-dependent KH channels and to cation-selective voltage-independent leak channels. The pulvinar KH channels were inhibited by external acidification (pH 7.8–5), in contrast to their acidification-promoted counterparts in guard cells. The inhibitory pH effect was resolved into a reversible decline of the maximum conductance and an irreversible shift of the voltage dependence of KH channel gating. The leak appeared acidification insensitive. External Cs (10 mm in 200 mmexternal K+) blocked both current types almost completely, but external tetraethylammonium (10 mm in 200 mm external K+) did not. Although these results do not link these two channel types unequivocally, both likely serve as K+ influx pathways into swelling pulvinar motor cells. Our results emphasize the importance of studying multiple model systems.

Plants sense positional changes relative to the gravity vector. To date, the signaling processes by which the perception of a gravistimulus is linked to the initiation of differential growth are poorly defined. We have investigated the role of inositol 1,4,5-trisphosphate (InsP3) in the gravitropic response of oat (Avena sativa) shoot pulvini. Within 15 s of gravistimulation, InsP3 levels increased 3-fold over vertical controls in upper and lower pulvinus halves and fluctuated in both pulvinus halves over the first minutes. Between 10 and 30 min of gravistimulation, InsP3 levels in the lower pulvinus half increased 3-fold over the upper. Changes in InsP3 were confined to the pulvinus and were not detected in internodal tissue, highlighting the importance of the pulvinus for both graviperception and response. Inhibition of phospholipase C blocked the long-term increase in InsP3, and reduced gravitropic bending by 65%. Short-term changes in InsP3 were unimpaired by the inhibitor. Gravitropic bending of oat plants is inhibited at 4°C; however, the plants retain the information of a positional change and respond at room temperature. Both short- and long-term changes in InsP3 were present at 4°C. We propose a role for InsP3 in the establishment of tissue polarity during the gravitropic response of oat pulvini. InsP3 may be involved in the retention of cold-perceived gravistimulation by providing positional information in the pulvini prior to the redistribution of auxin.

The skotonastic and phototropic responses of primary leaves of bean (Phaseolusvulgaris L.) were studied, using one primary leaf as an untreated control for its treated twin. A sudden, drastic step-down in photon fluence rate, FFR, resulted in the typical skotonastic down folding. The magnitude and kinetics of this responsewere independent of the preceding FFR as well as of the initial laminar elevation (attransition). The skotonastic response was eventually followed by increase in laminarelevation, as part of a progressive adaptation to the new (very low) FFR. The pulvinus exhibited positive and reversible phototropic curvature in response to adaxial and lateral exposure to high FFR. Adaxial exposure at different stages of its adaptation to low FFR resulted in very similar positive phototropic responses (rate and magnitude). At saturation, abaxial exposure of the pulvinus to equivalent FFR resulted in full reversal, to the same level as exposure of both sectors to low FFR, coinciding with the level of the...

Summary The pulvinus of bean ( Phaseolus vulgaris L) responds to unilateral photo-excitation by phototropic curvature. Osmotically active solutes and water are transported from its exposed to the opposite sector of its motor tissue, resulting in differential changes in turgor pressure in these sectors and generation of a trans-pulvinar torque. A null-point approach was used to non-invasively study these dynamic changes in the terminal leaflet of bean. A variable torque was applied perpendicular to the midrib, to restrain laminar movement by precisely and continuously counteracting the generated torque. This equilibrium prevented curvature of the pulvinus and the associated opposite axial changes in volume in the opposite sectors of its motor tissue. The laminar torques measured were used to estimate stresses (changes in turgor pressure) generated within the motor tissue. These stress values were used to derive the corresponding changes in osmotic pressures and in solute concentration. Skotonastically downfolded leaflets were excited with white light to study their combined dynamic response to photonastic and phototropic excitation. Photonastically unfolded (horizontal) leaflets were excited with blue and red light, alone and in combination, to determine the spectral dependence of the dynamic pulvinar responses tophototropic excitation by itself.

Leaflet movements in the mimosa-family tree Samanea saman stem from coordinated volume changes of cells in the leaf motor organs in the adaxial and abaxial motor cells (“flexors” and “extensors”). Shrinking, initiated by dissimilar light signals in extensors and in flexors, depends in both cell types on K+efflux via depolarization-dependent potassium (KD) channels. To compare between flexor and extensor KDchannels and to test for a possible interaction of these channels with the Ca2+-mobilizing phosphoinositide cascade evoked in these motor cells by the “shrinking signals,” we probed the channels with varying (5 nm–3 mm) cytosolic free-Ca2+ concentration ([Ca2+]cyt) in patch-clamped inside-out excised membrane patches. Ca2+ was not required for KD channel activation. [Ca2+]cytof 600 nm decreased the mean number of open KD channels in flexors, as monitored at −30 mV. Detailed analysis revealed that in flexors millimolar [Ca2+]cyt decreased the maximum number of open channels, but simultaneously increased KD channel opening probability by negatively shifting the half-maximum-activation voltage by 40 to 50 mV. Thus, the promoting and the inhibitory effects at millimolar [Ca2+]cyt practically cancelled-out. In contrast to flexors, none of the gating parameters of the extensor KD channels were affected by [Ca2+]cyt. Irrespective of [Ca2+]cyt, the steady-state gating of extensor KD channels was slightly but significantly more voltage sensitive than that of flexors. The unitary conductances of flexor and extensor KD channels were similar and decreased by approximately 20% at millimolar [Ca2+]cyt. It is intriguing that the extensor KD channels were significantly less K+selective than those in flexors.

The rhythmic leaflet movements of the plant Desmodium gyrans (L.f.) DC slow down in the presence of a static magnetic field. The leaflet positions were digitally retrieved from sequential CCD camera images of the moving leaflets. The experiments were performed under constant light (ca. 500 lux) and temperature (about 20 °C) conditions. The period of the leaflet was then around 5 min. Leaflets moving up and down in a magnetic field of approximately 50 mT flux density increased the period by about 10% due to a slower motion in the “up” position. Since during this position a rapid change of the extracellular potentials of the pulvinus occurs, it is proposed that the effects are mediated via the electric processes in the pulvinus tissue.

The leaves of Desmodium gyrans (L.F.) DC show circadian movements in the terminal and ultradian movements of the lateral leaflets. The movements are due to swelling and shrinking of motor cells in special organs. The anatomy of these pulvini is described for the lateral leaflets. Data from electrophysiological recordings using microelectrodes inserted into the lateral pulvini, together with treatments that affect the proton pumps and ion channels, have been used to develop a physiological model of the ultradian leaflet movement. It explains the oscillations in the motor cells as being due to a change between a pump state and depolarization. During the pump state, ions are taken up, causing water influx and swelling of the motor cells. Depolarization causes loss of ions and water efflux (the motor cells shrink). The roles of calcium and the phosphatidyl inositol signal chain are discussed on the basis of experiments using chemical agents that affect these processes. Since calcium oscillations are known to occur in organisms in both time and space, an attempt has been made to simulate the situation in Desmodium pulvini by a model of specially coupled oscillators. Effects of different other treatments of the lateral pulvini are discussed. Oscillations in the minute range seem to be more common and some might be related to turgor regulation and ion uptake comparable to the situation in Desmodium. The ultradian control of the lateral pulvini and the circadian control of the terminal pulvini are apparently based on different mechanisms.

Mature motor cells of Mimosa pudica that exhibit large and rapid turgor variations in response to external stimuli are characterized by two distinct types of vacuoles, one containing large amounts of tannins (tannin vacuole) and one without tannins (colloidal or aqueous vacuole). In these highly specialized cells we measured the abundance of two tonoplast proteins, a putative water-channel protein (aquaporin belonging to the [gamma]-TIPs [tonoplast intrinsic proteins]) and the catalytic A-subunit of H+-ATPase, using either high-pressure freezing or chemical fixation and immunolocalization. [gamma]-TIP aquaporin was detected almost exclusively in the tonoplast of the colloidal vacuole, and the H+-ATPase was also mainly localized in the membrane of the same vacuole. Cortex cells of young pulvini cannot change shape rapidly. Development of the pulvinus into a motor organ was accompanied by a more than 3-fold increase per length unit of membrane in the abundance of both aquaporin and H+-ATPase cross-reacting protein. These results indicate that facilitated water fluxes across the vacuolar membrane and energization of the vacuole play a central role in these motor cells.

In addition to circadian changes in the membrane potential and leaf movement, light applied to the pulvinus causes changes in both the membrane potential and the pulvinar movement in Phaseolus vulgar is L. Even after a short pulse of light, a transient depolarization of the membrane occurs and leaf movement is observed. Decreases of turgor pressure of the motor cells are always preceded by the depolarization. The direction of the leaf movement can be explained by the decrease of turgor pressure in the motor cells on the irradiated side of the pulvinus. Using the Okazaki Large Spectrograph at the National Institute for Basic Biology, we determined the action spectrum of the membrane depolarization induced by light pulses (30 s) in motor cells of Phaseolus. The pulvinus was left exposed to air during measurement of the membrane potential with microelectrodes. The action spectrum obtained was in the range of 300 to 730 nm. It had the highest peak at 460 nm with lower peaks at 380 nm and 420 nm. Almost no sensitivity was observed at wavelengths shorter than 360 nm and longer than 520 nm. Red and far-red light had no effect on the depolarization of the motor cell. The features of the action spectrum are almost the same as those of the Blue-Type response in plants.

The photonastic upward movement and scotonastic downward movement of the primary leaf of Phaseolus coccineus L. depends on ion fluxes across the plasma membrane of extensor and flexor cells of the laminar pulvinus. Extensor protoplasts cultured in 0.4 M mannitol, 10 mM KCI, 1 mM CaCl 2 , and 5 mM MES-KOH buffer pH 6 were found to swell upon switching on white light at the end of a 15 h dark period and to shrink upon switching off the light at the end of the following 9 h light period, behaviour consistent with that expected in the cells of intact plants. Light-induced swelling requires Ca 2+ in the surrounding medium. Both the Ca 2+ channel blocker verapamil and La 3+ inhibited this reaction, whereas TMB-8, an inhibitor of intracellular Ca 2+ transport, had no effect. When the Ca 2+ ionophore A 23187, the Ca 2+ channel agonist Bay K-8644, or thapsigargin, an inhibitor of Ca 2+ -ATPases at endo-membranes, was added to the medium, extensor protoplasts swelled in the dark. These results suggest that in extensor protoplasts light opens Ca 2+ channels in the plasma membrane and that the influx of extracellular Ca 2+ results in an increased cytoplasmic Ca 2+ concentration which is sufficient to mimic the light-on signal in activating or deactivating the ion transporters required for swelling. Dark-induced shrinking occurred in Ca 2+ -free medium. It was not inhibited by verapamil, but was by TMB-8. Both neomycin and Li + , substances which are known to inhibit the phosphoinositide pathway of transmembrane signalling, inhibited dark-induced shrinking. Myo-inositol nullified the Li + inhibition of dark-induced shrinking. Neither A 23187 nor Bay K-8644 induced shrinking in the light, but were able to nullify the inhibitory effect of TMB-8 on dark-induced shrinking. These results suggest that, in extensor protoplasts, the shrinking signal 'light off' is transduced through phosphoinositide hydrolysis and Ca 2+ release from internal stores. In addition to the inositol 1,4,5-trisphosphate (IP 3 )-induced increase of the cytoplasmic Ca 2+ concentration, further events depending on the light-off signal appear to be required for shrinking.

A theoretical model based on the water redistribution mechanism is proposed to predict the volumetric strain of motor cells in Mimosa pudica during the seismonastic movement. The model describes the water and ion movements following the opening of ion channels triggered by stimulation. The cellular strain is related to the angular velocity of the plant movement, and both their predictions are in good agreement with experimental data, thus validating the water redistribution mechanism. The results reveal that an increase in ion diffusivity across the cell membrane of

Leaf movements in Mimosa pudica, are in response to thermal stress, touch, and light or darkness, appear to be regulated by electrical, hydrodynamical, and chemical signal transduction. The pulvinus of the M. pudica shows elastic properties. We have found that the movements of the petiole, or pinnules, are accompanied by a change of the pulvinus morphing structures. After brief flaming of a pinna, the volume of the lower part of the pulvinus decreases and the volume of the upper part increases due to the redistribution of electrolytes between these parts of the pulvinus; as a result of these changes the petiole falls. During the relaxation of the petiole, the process goes in the opposite direction. Ion and water channel blockers, uncouplers as well as anesthetic agents diethyl ether or chloroform decrease the speed of alert wave propagation along the plant. Brief flaming of a pinna induces bidirectional propagation of electrical signal in pulvini. Transduction of electrical signals along a pulvinus induces generation of an action potential in perpendicular direction between extensor and flexor sides of a pulvinus. Inhibition of signal transduction and mechanical responses in M. pudica by volatile anesthetic agents chloroform or by blockers of voltage gated ion channels shows that the generation and propagation of electrical signals is a primary effect responsible for turgor change and propagation of an excitation. There is an electrical coupling in a pulvinus similar to the electrical synapse in the animal nerves.

2,4-dichlorophenoxyacetic (2,4-D) applied to excised leaves of Cassia fasciculata modified the dark-induced (scotonasty) and light-induced (photonasty) leaflet movements, showing that this compound acts on rapid turgor variation and the concomitant ion migrations, in particular K+. 2,4-D inhibited the scotonastic closure in a dose-dependent manner from 10−8 M to 10−5 M and promoted the photonastic opening in the same range of concentrations. The compound acted rapidly since a treatment as short as 5 min gave an obvious effect on the motile reaction; however, a lag period of 45–60 min was needed to observe its effect. Although 2,4-D is a weak acid, its greatest physiological efficiency was obtained with pH values close to neutrality. The physiological results are discussed in relation to the chemical properties and the characteristics of transport of the molecule.

Pulvinar motor cells ofPhaseolus vulgaris L display transient depolarization of the membrane potential and a turgor pressure decrease when exposed to a pulse of blue light. To analyze the mechanism of the transient depolarization, the effects of some factors such as anoxia, metabolic inhibitors and specific inhibitors of H+-ATPase have been examined. The findings have led to the conclusion that blue light inactivates the electrogenic H+-pumping ATPase in the plasma membrane of the motor cells. This inactivation seems to suppress ion uptake and decrease the turgor pressure of the motor cells.

Summary The light-driven responses of the terminal leaflet of bean were analyzed spectrally and functionally. Laminar elevation increases rapidly in response to continuous overhead exposure of its pulvinus to blue light. This response is enhanced in its early stages by simultaneous exposure to red light. The pulvinus responds similarly to continuous overhead unmixed red, or far-red light, albeit at much lower rates. The response to overhead red, alone, or during enhancement of the response to blue, was not affected by simultaneous far-red. However, the response to blue alone, or enhanced by mixture with red, was partially inhibited by simultaneous exposure to far-red. The results suggest that the response to blue resulted mostly from a blue-absorbing pigment system, but may involve some absorption by phytochrome, while responses to red or far-red, with and without blue, may be mediated by high-irradiance responses of phytochrome. Functional differences between the responses to red and blue become apparent when the abaxial (lower), or lateral sectors of the pulvinus are exposed to them, separately and in combination. These differences suggest that red controls the photonastic unfolding of the pulvinus, whereas blue controls its phototropic responses. These responses co-exist in the same tissue, but are separate and additive.

Gravitropic curvature of pulvini of wheat and oat stem segments gradually declined with decreasing atmospheric O₂ concentration and was almost completely blocked under anoxia, whereas that of rice stem segments was enhanced under hypoxia and anoxia. Anoxia substantially increased the ethanol content in pulvini of gravistimulated stem segments in rice, wheat and oat, but the ethanol content showed no marked difference between rice pulvini and wheat and oat pulvini. The concentrations of exogenous ethanol and acetaldehyde required to inhibit the gravitropic curvature of pulvini were significantly higher in rice segments than in wheat and oat segments. However, in all three species, the concentrations of ethanol and acetaldehyde required to completely inhibit curvature were several-fold higher than the endogenous levels that accumulated in pulvini gravistimulated in N₂. The pulvini of rice segments gravistimulated in N₂ did not contain much more ATP than those of wheat or oat segments gravistimulated in N₂. When applied unilaterally to the pulvini of vertically oriented stem segments incubated in N₂, indole-3-acetic acid induced bending in rice stem segments but not in wheat and oat stem segments. Transference of graviresponsive pulvini of rice, as well as those of wheat and oat, from aerobic conditions to anaerobic conditions led to cessation of gravitropic curvature within several minutes, but subsequently only gravitropic curvature of anoxic rice pulvini was completely recovered within 2 h. A large portion of this recovery was blocked by cordycepin, a transcription inhibitor. These results suggested that anoxia-induced expression of any gene or genes enables rice pulvini to respond to gravistimulation under anaerobic conditions, and that such a gene or genes might be unrelated to ethanol fermentation and ATP production in anaerobic conditions.

The pulvinus, located at the base of soybean leaflets, is both the light perception and motor organ for heliotropic leaf movements. Our objective was to investigate the role of plasma membrane H+/ATPase and TEA-sensitive K+ channels in mediating pulvinar response to light. The plasma membrane H+/ATPase activator, fusicoccin, plasma membrane H+/ATPase inhibitors, vanadate and erythrosin-B, and the K+ channel blocker TEA were introduced to the intact pulvinus through the transpiration stream. The pulvinus was illuminated by a vertical light beam of 1,400 .mol m-2 s-1 to stimulate leaf movement. Leaf orientation was measured every 5 min for 60 min of illumination. All compounds tested inhibited pulvinar bending, but concentration and uptake time required for inhibition varied: 12.5 F.M fusicoccin reduced leaf movement after 3 hr uptake, 2 mM vanadate reduced leaf movement after 6 hr uptake, 100 F.M erythrosin-B reduced leaf movement after 3 hr uptake, and 15 mM TEA reduced leaf movement after 6 hr uptake. In all cases final leaf angle was reduced by higher concentrations and/or increased time for uptake of the chemical into the pulvinus. Results support the hypothesis that the proximal mechanism of heliotropic movement is similar to that of nyctinastic movements. Paraheliotropism, orientation of the leaf lamina parallel

Immunocytochemical techniques were employed to study the spatial distribution of the plasma membrane H+-ATPase within various cell types of the young reactive primary pulvinus ofMimosa pudica L. These cells were interconnected by large numbers of plasmodesmata, being concentrated within pit-fields. Although we could routinely detect evidence of the H+-ATPase along the plasma membrane, immunolabelling was rarely, if ever, observed along the plasma membranes of the plasmodesmata. This finding is discussed with respect to the likely specialized supramolecular structure of the plasmodesma.

Blue/UV-A light regulates numerous physiological processes in plants. Several steps between the photo-excitation of the pigment involved and the physiological response are still unknown. Under irradiation by a laser beam (360 nm), a modification of the cell organization was observed in protoplasts isolated from motor cells of Mimosa pudica pulvini. Concomitantly with this macroscopic cell reaction, an early intracellular event was a transient increase in the cytoplasmic free calcium measured by cytofluorometric determination on indo-1-loaded protoplasts. This Ca 2+ mobilization was not significantly modified when protoplasts were incubated in a nominally calcium-free medium and was not inhibited by calcium antagonists (LaCl 3 and nifedipine) arguing thus for a mobilization from internal cellular stores.

Brassinosteroid (BR)-induced rice (Oriza sativa L.) lamina joint (RLJ) inclination and its relationship to indole-3-acetic acid (IAA) and ethylene were investigated using BR isolated from beeswax. The effect of BR on RLJ inclination was time- and concentration-dependent. Etiolated lamina were more sensitive to BR than green lamina. The BR-induced inclination was accompanied by increased lamina fresh weight, total water content, free-water content, proton extrusion and ethylene production, and decreased bound-water content. Lamina dry weight was not changed. The inclination was due to greater expansion of the adaxial cells relative to the dorsal cells in the lamina joint. This response was caused by BR and/or BR-induced signal(s) that were transported from the leaf sheath to the leaf blade. Both BR-induced RLJ inclination and ethylene production were inhibited by cobalt chloride (CoCl2), an inhibitor of ACC oxidase. BR-induced inclination was much higher than that of IAA, and was inhibited by high concentration of 2,3,5-triiodobenzoic acid (TIBA), an inhibitor of IAA transport. A synergistic effect was observed between BR and IAA. These results suggest that the effects of BR on RLJ inclination and pulvinus cell expansion may be resulted from BR-increased water potential and proton extrusion in the lamina. The BR-induced RLJ inclination may involve the action of ethylene but may be independent of IAA.

The circadian leaf movement of Phaseolus coccineus L. is mediated by ion fluxes across the plasma membrane of the pulvinar motor cells. H+‐ATPases and K+ channels of the plasma membrane are key molecules which produce the responses to external and internal signals by directing the flow of ionic osmotica for the swelling and shrinking of the pulvinar motor cells. We investigated the involvement of these molecules in the circadian rhythmicity of the Phaseolus pulvinus by testing the phase‐shifting effects and /or the period‐changing effects of inhibitors of the plasma membrane H+‐ATPase, of other treatments which reduce the H+ transport across the plasma membrane, and of the K+ channel blocker TEA on the leaf movement rhythm. Four hour pulses of vanadate (0.4 mM) and erythrosin B (8 pM), of low temperature (3–6 °C, down from an otherwise constant 23 °C) and of TEA (4 mM) shift the phase of the leaf movement rhythm. The phase response curves are similar in shape and resemble those for cyanide and az...

The circadian movement of the lamina of the primary leaf of Phaseolus coccineus is mediated by circadian volume changes of the extensor and flexor cells in the upper and lower half of the laminar pulvinus. Isolated protoplasts from the extensor, flexor, and flank cells of the pulvinus showed a circadian volume rhythm with a period longer than 24 h. In the case of the flexor protoplasts, we found a period length of 28 h, which is similar to that of the pulvinar cells in situ. In the extensor protoplasts, the volume rhythm was synchronized with 14-h light/10-h dark cycles. The larger volume was correlated with the early hours in the light period and the smaller volume with the dark period, as would be expected from the behavior of the extensor cells in situ.

Summary Movements of the terminal and lateral leaflets in the trifoliate leaf of pinto bean (Phaseolus vulgaris L.) cv. Bulgarian, in response to directional light, were studied by kinetic analysis. The pulvinule responds to unilateral light by contraction of the sector that intercepts the light and concomitant expansion of the opposite sector. The rate of the resulting laminar reorientation depends on the excitation of the photo-receptors in the pulvinule, which changes with angle of the incident light and as pulvinar topology changes in response to light. This dependence provides feed-back control of the eventual steady-state of the response. The pulvinule perceives directional light from all sides, but only as unilateral signals, and integrates these signals in its response. Phototropic responses of the pulvinule are modified by its asymmetry, which differs in the terminal and lateral leaflets. The asymmetry is expressed by axial torsion, superimposed on the positive phototropic curvature. The resulting laminar reorientations reflect this asymmetry. Laminar reorientation in directional light is a passive result of the pulvinar response and may combine changes in azimuth and axial rotation with changes in elevation.

When treated with various calcium-active agents, the volume changes in the tannin vacuoles of the abaxial (lower) motor cells in the sensitiveMimosa pudica L. correspond to the movement of the primary pulvinus. The calcium pump inhibitors, sodium metavanadate and erythrosin B, significantly inhibited the rate of recovery in both the in vivo and in vitro examinations, while the calcium channel blocker, verapamil, inhibited the closing response. Bay-K 8644 enhanced the in vivo effect and induced the in vitro effect, therefore appearing to be an agonist of the voltage regulated calcium channels in the tannin vacuoles. These observations support the hypothesis that calcium channels in the tannin vacuole membrane underly the thigmonastic response and pumps in the tannin vacuole membrane are involved in the mechanisms underlying recovery.