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Transport processes in stimulated and non-stimulated leaves of Mimosa pudica - II. Energesis and transmission of seismic stimulations
Abstract
Adenosine diphosphate (ADP), adenosine triphosphate (ATP) and orthophosphate were determined in non-stimulated, stimulated and relaxed pulvini of mature Mimosa pudica L. leaves. Additional determinations were made with leaflets, rhachillae, petiole and the stem in the stimulated condition. Results show that the content of adenine nucleotides is approximately twice as high in the pulvini as in the tissues between the pulvini. Orthophosphate, in contrast, occurs at higher concentrations in the connecting tissues than in the pulvini. ATP content is highest in the primary pulvini (0.8 μmol/mg dry wt.) and lowest in the tertiary pulvini. Stimulation causes consumption of ATP with a simultaneous increase in ADP content; however, the response is different in each type of pulvinus. This difference is best expressed in the ATP:ADP ratio. Stimulation causes the most marked reduction of the ratio (9.5-1.4) in the secondary pulvini which react nyctinastically. Orthophosphate content is reduced by stimulation in all types of pulvini, and is increased during the recovery phase. By using a stylet bundle severed from a feeding aphid by a laser shot as tip for the microelectrode, changes of sieve tube membrane potentials were recorded. The changes of the electropotentials following stimulation show that the sieve tube is the pathway for the transmission of the excitation signal in the form of an action potential.
... Then outward rectifying K + channel would repolarize the membrane (Yan et al. 2009). In higher plants, the APs can travel over short as well as long distances through plasmodesmata and phloem, respectively (Sibaoka 1962(Sibaoka , 1991Fromm and Eschrich 1988b;Fromm and Lautner 2007). ...
... When the tip of leaf pinna in M. pudica is stimulated by cooling, touching, or electrically (Volkov et al. 2010) an AP is evoked and transmitted basipetally with a speed 20-30 mm s -1 , what results in leaflet folding by a sudden loss of turgor pressure in the motor cells of the pulvinus (Fig. 2.6a, Eschrich 1988c, Fromm and. In contrast to D. muscipula, where all the major tissues of trap lobes (sensory cells of trigger hairs, upper, and lower epidermis, mesophyll cells) are excitable with similar resting potentials (150-160 mV, Hodick and Sievers 1988), excitable cells in Mimosa are found in vascular bundles and pulvinus (Sibaoka 1962;Samejima and Sibaoka 1983;Fromm and Eschrich 1988b). In Mimosa, the phloem and pulvinus is surrounded by sclerenchyma and collenchyma sheath to restrict electrical signaling to phloem and lateral propagation (Fleurad-Lessard et al. 1997;Fromm 2006;Fromm and Lautner 2007). ...
... Propagation of electrical signals in plants is costly. In M. pudica, the ATP level is much higher in pulvini than in the tissue between pulvini and stimulation causes consumption of ATP with simultaneous increase in ADP content (Lyubimova et al. 1964;Fromm and Eschrich 1988b). During the 1-3 s required for trap closure in D. muscipula 29% of ATP is lost (Jaffe 1973;Williams and Bennett 1982). ...
Electrical signals are initial response of plant to the external stimuli.
This type of signal may trigger different physiological responses. The most famous
is the rapid leaf movement in carnivorous and sensitive plants. However, a lot of
less visible changes in plant physiology may occur. This chapter focuses on the
effect of action (APs) and variation potentials (VPs) on photosynthesis and respiration.
First, experimental methods and setup for measurements of photosynthesis
and respiration in response to electrical signals are described. Then detailed
information about effect of AP and VP on CO2 metabolism in different plant
species are summarized. Both light and dark reactions of photosynthesis, as well as
rate of respiration, are affected by electrical signals, but the effect is often adverse
(from inhibition to stimulation of photosynthesis). In addition, the stomatal conductance
(gs), an important component of gas exchange, is also differently affected
by electrical signals. Summarizing the data from numerous authors, the hypothesis
about mechanism underlying photosynthetic limitation and stimulation of respiration
is proposed.
... In animal nervous systems, a neuron rapidly transmits a signal to its neighbors via electrical action potentials. Similar self-propagating, transient changes in membrane potential have been detected in many plant species Fromm and Lautner 2007) in addition to classic electrophysiological models such as M. pudica (Fromm and Eschrich 1988;Samejima and Sibaoka 1982;Sibaoka 1962), Venus flytrap (Hodick and Sievers 1988), and green algae with giant cells (Lunevsky et al. 1983). Although the propagation speeds of electrical signals in plants (typically ranging from centimeters to millimeters per second) ) are much slower than those of their animal counterparts (up to tens of meters per second), they still represent one of the fastest signaling events in plants. ...
... Although the propagation speeds of electrical signals in plants (typically ranging from centimeters to millimeters per second) ) are much slower than those of their animal counterparts (up to tens of meters per second), they still represent one of the fastest signaling events in plants. Cells in the vascular system, especially sieve tube elements in the phloem, are thought to be the major pathways of rapid electrical signals (Fromm and Eschrich 1988;Fromm and Lautner 2007;Hedrich et al. 2016;Nguyen et al. 2018;Samejima and Sibaoka 1983). The elongated, cytoplasmically connected cell structures of the vascular system and its network throughout the plant body make the vascular system suitable for long-distance electrical communication, in addition to other systemic signaling mediated by molecular transport or the direct transmission of hydraulic pressure . ...
Plant movements are generally slow, but some plant species have evolved the ability to move very rapidly at speeds comparable to those of animals. Whereas movement in animals relies on the contraction machinery of muscles, many plant movements use turgor pressure as the primary driving force together with secondarily generated elastic forces. The movement of stomata is the best-characterized model system for studying turgor-driven movement, and many gene products responsible for this movement, especially those related to ion transport, have been identified. Similar gene products were recently shown to function in the daily sleep movements of pulvini, the motor organs for macroscopic leaf movements. However, it is difficult to explain the mechanisms behind rapid multicellular movements as a simple extension of the mechanisms used for unicellular or slow movements. For example, water transport through plant tissues imposes a limit on the speed of plant movements, which becomes more severe as the size of the moving part increases. Rapidly moving traps in carnivorous plants overcome this limitation with the aid of the mechanical behaviors of their three-dimensional structures. In addition to a mechanism for rapid deformation, rapid multicellular movements also require a molecular system for rapid cell-cell communication, along with a mechanosensing system that initiates the response. Electrical activities similar to animal action potentials are found in many plant species, representing promising candidates for the rapid cell–cell signaling behind rapid movements, but the molecular entities of these electrical signals remain obscure. Here we review the current understanding of rapid plant movements with the aim of encouraging further biological studies into this fascinating, challenging topic.
... These studies reported that excitable cells in petioles were parenchyma cells in the protoxylem and parenchyma or companion cells in the phloem [42,43]. Using an aphid stylet as a passage to the sieve tube in the petiole, the transmission of the action potential was also confirmed in the sieve tube [44]. These vascular excitable cells should contribute to the propagation of the action potential in M. pudica [42][43][44]. ...
... Using an aphid stylet as a passage to the sieve tube in the petiole, the transmission of the action potential was also confirmed in the sieve tube [44]. These vascular excitable cells should contribute to the propagation of the action potential in M. pudica [42][43][44]. Samejima and Sibaoka [24] attempted to understand the relationship between the generation of the action potential and the ion composition (ion strength) in the extracellular fluid in which the target tissues were immersed. They found that the amplitudes of the action potentials recorded from excitable protoxylem cells in the petioles were affected by external Cl − concentration [24]. ...
As sessile organisms, plants do not possess the nerves and muscles that facilitate movement in most animals. However, several plant species can move quickly in response to various stimuli (e.g., touch). One such plant species, Mimosa pudica L., possesses the motor organ pulvinus at the junction of the leaflet-rachilla, rachilla-petiole, and petiole-stem, and upon mechanical stimulation, this organ immediately closes the leaflets and moves the petiole. Previous electrophysiological studies have demonstrated that a long-distance and rapid electrical signal propagates through M. pudica in response to mechanical stimulation. Furthermore, the spatial and temporal patterns of the action potential in the pulvinar motor cells were found to be closely correlated with rapid movements. In this review, we summarize findings from past research and discuss the mechanisms underlying long-distance signal transduction in M. pudica. We also propose a model in which the action potential, followed by water flux (i.e., a loss of turgor pressure) in the pulvinar motor cells is a critical step to enable rapid movement.
... Moreover, an AP controlling the leaf movements also triggers phloem unloading of sucrose (132). It appears that with the transmission of excitation through the phloem the flow of assimilates stops, sucrose enters the apoplast and the excited cells shrink (129,(132)(133). As a matter of fact, the temporal loss of photoassimilates seems to control all movements of Mimosa (nyctinasty, thigmonasty, gravitropism), since they all depend on turgor changes. ...
... With intracellular impalements, the difficulties may also begin when the exact positioning of a measuring electrode is important while working on an intact plant. This problem was solved by Wright and Fisher who used aphid's stylets to penetrate the phloem exclusively (253); the procedure was so suitable that it was used by the others, as well (132)(133)(134). Equally prosperous is the method of placing the measuring electrode into substomatal cavities of the open stomata nearby an AP-conductive tissue (219,244,252). ...
For many years the physiological significance of electrical signalling in plants has been neglected, even though the very first action potentials (APs) were recorded in insectivorous plants in 1873 (1). Still many aspects of plant excitability are not sufficiently well elaborated. However, nowadays it is common knowledge that in animals as well as in plants: (i) ion fluxes through plasma membrane provide AP biophysical bases; (ii) AP transmission is electrotonic, without a decrement and is followed by a refractory period; (iii) there is an “all-or-nothing” principle fulfilled, with an exponential dependency of threshold stimulus strength on stimulus duration; (iv) APs are initiated and propagated by excitable tissues to control a plethora of responses indispensable for growth, nutrient winning, reproduction, and defence against biotic and abiotic challenges. AP can be viewed as a burst of electrical activity that is dependent on a depolarizing current. In plants the depolarization phase of AP consists of Cl⁻- and Ca²⁺-fluxes. The following phase-a repolarization-relies in turn on K⁺ fluxes and active H⁺ flows that both drive membrane potential back to more negative values. Thus, the AP mechanism is electrochemically governed by the selective properties of the plasma membrane with ion selective conduits as key players. A more detailed understanding of how these membrane proteins work hand in hand during excitation and signal transduction is eagerly awaited. The existence of ion channels was first hypothesized by Alan Hodgkin and Andrew Huxley (2-8), and next confirmed with a patch-clamp technique by Erwin Neher and Bert Sakmann (9). These experiments though conducted on neurons and muscles, respectively, prompted plant electrophysiology as well. Since then substantial evidence for APs in a wide array of plants has been emerging and consequently growing in number.
... The movements of M. pudica are not only triggered by touch but also follow the diurnal cycles with the pulvini folding in absence of light [65]. Touch related movements involve the primary and tertiary pulvini while the sleep movements involve all the pulvini [71]. The three types of pulvini allow two different typologies of planar deformation: upward or downward. ...
... The three types of pulvini allow two different typologies of planar deformation: upward or downward. The primary and secondary pulvini deform downward while tertiary pulvini deform upward [ 65,66,71]. This planarity has been confirmed for the tertiary pulvinus by observation of the cellular layout. ...
While plants are primarily sessile at the organismal level, they do exhibit a vast array of movements at the organ or sub-organ level. These movements can occur for reasons as diverse as seed dispersal, nutrition, protection or pollination. Their advanced mechanisms generate a myriad of movement typologies, many of which are not fully understood. In recent years, there has been a renewal of interest in understanding the mechanical behavior of plants from an engineering perspective, with an interest in developing novel applications by up-sizing these mechanisms from the micro- to the macro-scale. This literature review identifies the main strategies used by plants to create and amplify movements and anatomize the most recent mechanical understanding of compliant engineering mechanics. The paper ultimately demonstrates that plant movements, rooted in compliance and multi-functionality, can effectively inspire better kinematic/adaptive structures and materials. In plants, the actuators and the deployment structures are fused into a single system. The understanding of those natural movements therefore starts with an exploration of mechanisms at the origins of movements. Plant movements, whether slow or fast, active or passive, reversible or irreversible, are presented and detailed for their mechanical significance. With a focus on displacement amplification, the most recent promising strategies for actuation and adaptive systems are examined with respect to the mechanical principles of shape morphing plant tissues.
Available on https://hal-enpc.archives-ouvertes.fr/hal-01618277
... K + is an essential monovalent cation for plant growth and development and a key ion for regulating osmotic balance in cells [19,42]. Using energy-dispersive X-ray microanalysis, the content of K + and Cl − in the primary pulvinus tissues of M. pudica were analyzed, and the results showed that the concentration of K + in the apoplast of external extensor cells decreased significantly, while changes in the Cl − content were less striking in the pulvinus [6,85]. The accumulation of ions in the apoplast seems to be initiated by the decrease in water potential triggered by an apoplastic accumulation of unloaded sucrose [32]. ...
Leaf movement is a manifestation of plant response to the changing internal and external environment, aiming to optimize plant growth and development. Leaf movement is usually driven by a specialized motor organ, the pulvinus, and this movement is associated with different changes in volume and expansion on the two sides of the pulvinus. Blue light, auxin, GA, H+-ATPase, K+, Cl−, Ca2+, actin, and aquaporin collectively influence the changes in water flux in the tissue of the extensor and flexor of the pulvinus to establish a turgor pressure difference, thereby controlling leaf movement. However, how these factors regulate the multicellular motility of the pulvinus tissues in a species remains obscure. In addition, model plants such as Medicago truncatula, Mimosa pudica, and Samanea saman have been used to study pulvinus-driven leaf movement, showing a similarity in their pulvinus movement mechanisms. In this review, we summarize past research findings from the three model plants, and using Medicago truncatula as an example, suggest that genes regulating pulvinus movement are also involved in regulating plant growth and development. We also propose a model in which the variation of ion flux and water flux are critical steps to pulvinus movement and highlight questions for future research.
... Pulvinus-driven leaf folding can occur gradually over the course of hours under the influence of a circadian rhythm, or rapidly as a thigmonastic response to touch, shaking, or wounding of a plant. Active pulvinus bending is associated with efflux of K + and Cl À ions from parenchyma cells, 2 offloading of sugar from vascular elements, 3 and consumption of ATP, 4 indicating that pulvinus motion is associated with active transport of ions and other osmolites to which water is attracted. 5 While multiple theoretical models of pulvinus physiology provide insight into the biochemical mechanisms that power active movement of fluid between parenchyma cell groups, 6-9 relatively little is known regarding the mechanisms by which volumetric changes at the cellular level are translated into physiologically useful motion at the organ scale. ...
Leaf movement in vascular plants is executed by joint-like structures called pulvini. Many structural features of pulvini have been described at subcellular, cellular, and tissue scales of organization; however, how the characteristic hierarchical architecture of plant tissue influences pulvinus-mediated actuation remains poorly understood. To investigate the influence of multiscale structure on turgor-driven pulvinus movements, we visualized Mimosa pudica pulvinus morphology and anatomy at multiple hierarchical scales of organization and used osmotic perturbations to experimentally swell pulvini in incremental states of dissection. We observed directional cellulose microfibril reinforcement, oblong, spindle-shaped primary pit fields, and longitudinally slightly compressed cell geometries in the parenchyma of M. pudica. Consistent with these observations, isolated parenchyma tissues displayed highly anisotropic swelling behaviors indicating a high degree of mechanical anisotropy. Swelling behaviors at higher scales of pulvinus organization were also influenced by the presence of the pulvinus epidermis, which displayed oblong epidermal cells oriented transverse to the pulvinus long axis. Our findings indicate that structural specializations spanning multiple hierarchical scales of organization guide hydraulic deformation of pulvini, suggesting that multiscale mechanics are crucial to the translation of cell-level turgor variations into organ-scale pulvinus motion in vivo.
... Pulvinus-driven leaf folding can occur gradually over the course of hours under the influence of 27 a circadian rhythm, or rapidly as a thigmonastic response to touch, shaking, or wounding of a 28 plant. Active pulvinus bending is associated with efflux of K + and Clions from parenchyma cells 29 (Kumon and Suda, 1984), offloading of sugar from vascular elements (Fromm and Eschrich, 30 1988a), and consumption of ATP (Fromm and Eschrich, 1988b), indicating that pulvinus motion 31 is associated with active transport of ions and other osmolites to which water is attracted 32 (Scorza and Dornelas, 2011). 33 ...
Mechanistic studies of animal and plant motion often focus on the fundamental units of biological actuation: individual motor cells. Recent advances spanning the fields of muscle physiology and biomimetic actuation, however, reveal that important mechanical behaviors also arise at higher levels of organization, driven by the interplay of motor cells with connective tissue networks that guide and control en masse deformation. Here we illustrate how a paradigm of cell-driven actuation augmented by a mechanically crucial extracellular matrix is equally applicable to plant pulvini; motor organs evolutionarily distinct from but mechanically analogous to animal muscles. Using pulvini from the sensitive plant Mimosa pudica , we visualized anatomical sources of mechanical anisotropy at three hierarchical scales of pulvinus organization, built hydraulic physical models of observed morphologies, and analyzed 3D changes in the shapes of osmotically pressurized pulvini. We find that extracellular guidance controls the direction and extent of turgor-induced pulvinus deformation, an effect that ultimately influences the magnitude, speed, and energetic cost of pulvinus-driven motion. We discuss the relevance of these findings to ongoing work in the fields of muscle physiology and soft robotics, and we situate pulvini within a conceptual framework for understanding the design of biological motor organs generally.
... Studies with 14 C labelled acrylamide (Kalinin et al. 1970), application of blocks (surgical and chemical) (Kalinin et al. 1970), microelectrodes (Eschrich et al. 1988) and studies of the electrochemical gradient of ions in conducting boundless (Opritov and Retivin 1982;Retivin and Opritov 1986) pointed to phloem cells as the most predestinated to generate and transmit excitation. Fromm and Bauer (1994), applying cut off aphid stylets, inserted through them microelectrodes precisely into sieve tubes of Zea mays and Mimosa pudica (Fromm and Eschrich 1988b). Examination of transmission routes of APs by this method allowed them to find that transmission of bioelectrical potentials takes place along the symplasmic route of phloem, though it does not exclude the participation of other plant tissues. ...
Plants are subject to stimuli from the environment on which they strongly depend and in contrast to animals, they are unable to escape harmful influences. Therefore, being able to receive stimuli they have developed adequate responses to them. Such a reaction can occur in the area of a stimulus action or cover the whole plant or its parts. In the latter case, it is a systemic reaction. The plant reaction is expressed by various intensity, rate and kind of response. It is interesting to know the character of the signal informing about a stimulus, the routes of its propagation and the transmission mechanism. Three conceptions of excitation are distinguished: 1) propagation of chemical agents formed at the site of a stimulus action with the flow of the phloem sap or through the atmosphere (in the case of volatile substances) to other plant parts, 2) a very fast transmission by the xylem in the wave of hydraulic pressure formed after a plant damage. From combining the "hydraulic" and "chemical" hypothesis a con-ception of hydraulic dispersion has been formulated which assumes that chemical substances synthetized after an injury can be transferred very fast with the wave of hydraulic pressure changes in the whole plant, 3) a stimulus evokes the action potential (AP), and its transmission along the whole plant, plant organ or specialized tissue, by local circuits from cell to cell. Strong, damaging stimuli can evoke variation potentials (VPs), the character of which differs from APs. It is postulated that transmission of VP occurs by a hydraulic dispersion and electrical changes seem to be secondary phenomena.
... Pharmacological and cytological studies indicate that fragmentation of the actin cytoskeleton [16,17], dephosphorylation of its tyrosine residues [17,18], and changes in Ca 2+ level [10,19] in pulvinar motor cells participate in the movement. The seismonastic reaction can be propagated over a distance by an electrical action potential [20], which is likely transmitted through the protoxylem [20,21] and the phloem [22]. Chemical substance(s) also contribute to the long-range transmission of the movement [23] and several candidate substances were identified by chemical analysis and bioassays [24,25]. ...
The sensitive plant Mimosa pudica has long attracted the interest of researchers due to its spectacular leaf movements in response to touch or other external stimuli. Although various aspects of this seismonastic movement have been elucidated by histological, physiological, biochemical, and behavioral approaches, the lack of reverse genetic tools has hampered the investigation of molecular mechanisms involved in these processes. To overcome this obstacle, we developed an efficient genetic transformation method for M. pudica mediated by Agrobacterium tumefaciens (Agrobacterium). We found that the cotyledonary node explant is suitable for Agrobacterium-mediated transformation because of its high frequency of shoot formation, which was most efficiently induced on medium containing 0.5 µg/ml of a synthetic cytokinin, 6-benzylaminopurine (BAP). Transformation efficiency of cotyledonary node cells was improved from almost 0 to 30.8 positive signals arising from the intron-sGFP reporter gene by using Agrobacterium carrying a super-binary vector pSB111 and stabilizing the pH of the co-cultivation medium with 2-(N-morpholino)ethanesulfonic acid (MES) buffer. Furthermore, treatment of the explants with the detergent Silwet L-77 prior to co-cultivation led to a two-fold increase in the number of transformed shoot buds. Rooting of the regenerated shoots was efficiently induced by cultivation on irrigated vermiculite. The entire procedure for generating transgenic plants achieved a transformation frequency of 18.8%, which is comparable to frequencies obtained for other recalcitrant legumes, such as soybean (Glycine max) and pea (Pisum sativum). The transgene was stably integrated into the host genome and was inherited across generations, without affecting the seismonastic or nyctinastic movements of the plants. This transformation method thus provides an effective genetic tool for studying genes involved in M. pudica movements.
... Leaflets collapse in seconds, and not in tens of minutes, as in rhythmic movements. This peculiar quick movement is thought to result from a abrupt sucrose unloading from phloem addicted to the extensor apoplast, rising the osmotic drive for water efflux from cells 22 and/or ultrafiltration of water out of the cells due to sudden squeezing achievement exerted by activated cytoskeletal elements. 23 The very fast movement of the leaves of Venus fly trap, occurring in an 100 ms range -is another case of different process: according to Forterre 24 the osmotic motor performs a relatively trivial function: only that of shifting the setting point of the elastically unsteady leaf, already inherently hanging for snapping. ...
Some studies showed that anesthetics reduce the response of physical stimuli in Mimosa pudica and in Venus Flytrap (Dionaea muscipula), peculiar plants that have the ability to respond to touch stimuli. In this research we tested the effects of ketamine, lidocaine, diethyl ether, and amlodipine on the movements of Mimosa pudica and Venus Flytrap. With a literature review, we tried to bring elements to theorize about the interaction of these substances with these plants. The angular displacement in Mimosa´s petiole and in Dionaea leaves is what was measured to compare the drugs group with control groups.
Living structures constantly interact with the biotic and abiotic environment by sensing and responding via specialized functional parts. In other words, biological bodies embody highly functional machines and actuators. What are the signatures of engineering mechanisms in biology? In this review, we connect the dots in the literature to seek engineering principles in plant structures. We identify three thematic motifs-bilayer actuator, slender-bodied functional surface, and self-similarity-and provide an overview of their structure-function relationships. Unlike human-engineered machines and actuators, biological counterparts may appear suboptimal in design, loosely complying with physical theories or engineering principles. We postulate what factors may influence the evolution of functional morphology and anatomy to dissect and comprehend better the why behind the biological forms.
Pulvini are plant motor organs that fulfill two conflicting mechanical roles. At rest, pulvini function as rigid beams that support the cantilevered weight of leafy appendages. During thigmonastic (touch-induced) or nyctinastic (“sleep”-induced) plant movements, however, pulvini function as flexible joints capable of active bending. I hypothesized that the ability to alternate between these roles emerges from the interaction of two structural features of pulvini: anisotropically reinforced parenchyma cells comprising the body of the pulvinus, and a longitudinally stiff but flexurally pliant vascular bundle running through the pulvinus core. To investigate how these two components might interact within biological pulvini, I built a set of pulvinus-inspired physical models with varying combinations of these elements present. I compared the abilities of the models to 1.) resist imposed bending deformation (i.e., act as rigid beams) and 2.) exhibit bending deformation when asymmetrically pressurized (i.e., act as actively deformable joints). Pulvinus models displayed the greatest ability to resist bending deformation when both an anisotropically reinforced parenchyma and a vasculature-like core were present. Disruption of either element reduced hydrostatic fluid pressures developed within the models, resulting in a decreased ability to resist externally applied forces. When differentially pressurized to induce active bending, the degree of bending achieved varied widely between models with and without adequately reinforced parenchyma elements. Bending, however, was not influenced by the presence of a vasculature-like core. These findings suggest that biological pulvini achieve their dual functionality by pairing anisotropically reinforced parenchyma tissues with a longitudinally stiff but flexurally pliant vascular core. Together, these elements compose a hydrostatic skeleton within the pulvinus that strongly resists external deformation when pressurized, but that bends easily when the balance of fluid pressures within it is altered. These results illustrate the emergent nature of pulvinus motor abilities and highlight structural specialization as an important aspect of pulvinus physiology.
In contrast to chemical messengers, electrical signals such as action potentials and variation potentials can transmit information much faster over long distances. Electrical signals can be triggered by various abiotic stress factors and are propagated via plasmodesmata over short distances and within the phloem over long distances. Thus, in addition to assimilate transport from sources to sinks, the phloem serves as a communication highway for various types of information. Key factors for systemic signaling in the phloem are peptides, RNAs, hormones, and electrical signals. In recent years, there has been increasing evidence that rapid communication by means of electrical signals is essential for various plant physiological processes. Thus, this chapter focuses on electrical signaling and various associated physiological effects, such as regulation of leaf movements, assimilate transport, photosynthesis, and gas exchange, as well as plant water status.Key wordsAction potential Aphid technique Assimilate transport Gas exchange Long-distance signaling Variation potential
Minerals and organic materials present in soil are responsible for regulatory activity of cell organelles. Micronutrients such as zinc, boron, copper, iron, manganese, molybdenum and chlorine are readily absorbed and found in lower concentrations in plant tissues. Micronutrients reduce ion toxicity, preserve water balance, improve mineral uptake and assimilation, modify various gas exchange traits and reduce oxidative stress in plants. Plants contain sufficient micronutrients that possess greater tolerance capacity towards abiotic stress. The response of micronutrient application to various abiotic stresses depends on the crop, growth stage and concentration of the nutrient solution. This chapter explains the significance of micronutrients in crop production and their ability against the abiotic stress in plants.
As plants are living forms that cannot communicate their condition (stress, requirements) as animals, they have been studied to find chemical or physical signals that could help understand the plant requirements for several purposes such as substances and food production. Different research supports electrical signals (ES) related to different stress conditions in plants as damage or drought. Some others have identified and classified these signals generated by stress condition using diverse Artificial intelligence (AI) techniques. Finally, some other researches have used electricity as a stimulator obtaining a response as chemical compounds production, gene expression and growth-promoting. In a few words, ES from plants can be interpreted, which could also be sent back to plants. Based on the bibliographic revision in this work, it is proposed that experiments and research, where the ES serves to activate chemical and physiological mechanisms or as elicitor, are required to consider the electrical signals as a possible communication pathway with plants.
Plants possess a systemic signaling system whereby local stimuli can lead to rapid, plant-wide responses. In addition to the redistribution of chemical messengers that range from RNAs and peptides to hormones and metabolites, a communication system acting through the transmission of electrical, Ca2+, reactive oxygen species and potentially even hydraulic signals has also been discovered. This latter system can propagate signals across many cells each second and researchers are now beginning to uncover the molecular machineries behind this rapid communications network. Thus, elements such as the reactive oxygen species producing NAPDH oxidases and ion channels of the two pore channel, glutamate receptor-like and cyclic nucleotide gated families are all required for the rapid propagation of these signals. Upon arrival at their distant targets, these changes trigger responses ranging from the production of hormones, to changes in the levels of primary metabolites and shifts in patterns of gene expression. These systemic responses occur within seconds to minutes of perception of the initial, local signal, allowing for the rapid deployment of plant-wide responses. For example, an insect starting to chew on just a single leaf triggers preemptive antiherbivore defenses throughout the plant well before it has a chance to move on to the next leaf on its menu.
The sessile nature of plants has provided for unique adaptations to their surrounding environments. Over their evolutionary course, plants have survived by changing their functional or structural properties. Animals, being mobile, can change their circumstances to an extent, but plants do not have brains, nervous systems, or muscles. Plants are not, however, static; they are able to respond to a variety of environmental stimuli. They perform various macroscopic and microscopic movements in response to intrinsic and extrinsic stimuli.
In the previous report (Komor 1983 in Prog Bot 45:68-75) it was emphasized that phloem transport is inevitably related to membrane transport processes. However, the mechanism of longitudinal assimilate movement in sieve tubes is still explained either on the basis of Münch’s (1930) pressure-flow theory, or on the basis of various theoretical calculations which neglect the fact that sieve elements are living cells of a system which is everywhere and completely surrounded by a plasma membrane (Rand and Cooke 1978).
In higher plants at least three different types of electrical long-distance signaling exist: action potential (AP), variation potential (VP), and system potential (SP), all of which have their own characteristics concerning their generation, duration, amplitude, velocity, and propagation. Whereas both AP and VP are due to a transient depolarization of the plasma membrane, the SP is based on hyperpolarization. For more than 100 years the AP is known and described for some specialized plants such as the Venus flytrap. Meanwhile, all three types of electrical signaling have been shown for many common plants, monocots as well as dicots, indicating that the capability to generate long-distance electrical signals is not the exception but a general physiological feature of plants. In spite of this, positive proofs for the involvement of these kinds of electrical signaling in the induction of many different plant responses to (a)biotic stresses or in developmental processes still wait to be established.
Leaf movements of many plant species are mediated by curvatures of pulvini, located at the base of petioles and laminae. In pulvini, the central vascular core is surrounded by parenchymous cortex cells. The curvatures of pulvini are brought about by the coordinated and simultaneous swelling and shrinking of the cortex cells (the motor cells) in two opposing halves of the pulvinus. Motor cells that are expanded axially in the horizontal day (open, unfolded) position of leaves or leaflets are designated extensor cells, those that are contracted axially in the respective position flexor cells. Depending on whether the leaves (pulvini) move to their vertical night position (closed, folded position) downwards (e.g., secondary pulvini of Phaseolus and Samanea), or upwards (e.g., secondary pulvini of Cassia), the extensor cells are located in the lower (abaxial) or upper (adaxial) half of the pulvinus.
This review explores the relationship between electrical long-distance signaling and the potential consequences for physiological processes in plants. Electrical signals such as action potentials (APs) and variation potentials (VPs) can be generated by spontaneous changes in temperature, light, touch, soil water content, by electrical as well as chemical stimulation or by wounding. An AP is evoked when the stimulus is sufficiently great to depolarize the membrane to below a certain threshold, while VPs are mostly induced by wounding, which induces a hydraulic wave transmitted through the xylem, thereby causing a local electrical response in the neighboring symplastic cells. Once generated, the signal can be transmitted over short distances from cell-to-cell through plasmodesmata, and after having reached the phloem it can also be propagated over long distances along the sieve tube plasma membrane. Such electrical messages may have a large impact on distant cells, as numerous well-documented physiological effects of long-distance electrical signaling have been shown. Electrical signals, for instance, affect phloem transport as well as photosynthesis, respiration, nutrient uptake, and gene expression. © 2012 Springer-Verlag Berlin Heidelberg. All rights are reserved.
Electrical signalling along the phloem has been studied in a number of species like maize, willow and Mimosa. It appears that sieve tubes with their large sieve pores are used to transmit information over long distances, while plasmodesmata serve as a means for the propagation of electrical signals over short distances between cells. By using the aphid technique the phloem pathway has been shown to transmit action potentials with a velocity up to 10 cm s-1. With regard to the ion fluxes which create the conditions necessary for the generation of an action potential, we found that calcium influx as well as potassium and chloride efflux are involved. Some of their corresponding ion channels were identified. AKT2/3-like channels, expressed in the phloem and capable of mediating both uptake and release of K+ in response to changes in membrane potential, were identified in several species such as Arabidopsis, maize and broad bean. Concerning physiological functions of electrical signalling, evidence was found for a link between the signals and photosynthetic response in Mimosa, apart from the regulation of rapid leaf movements. In addition, electrical signals in maize play a role in the regulation of phloem transport as well as in root-to-shoot communication of entire plants.
Action potentials generated spontaneously (SAPs) and evoked by electrical stimulation (APs) in tomato plants (Solanum lycopersicum L.) cv. Micro-Tom ABA-deficient mutants (sitiens—MTsit) and its wild type (MTwt) were characterized by continuous monitoring of electrical activity for 66 h and by application of an electrical stimulation supplied extracellularly. MTsit generated SAPs which spread along the stem, including petioles and roots with an amplitude of 44.6 ± 4.4 mV, half-time (t½) of 33.1 ± 2.9 s and velocity of 5.4 ± 1.0 cm min−1. Amplitude and velocity were 43 and 108 % higher in MTsit than in MTwt, respectively. The largest number of SAPs was registered in the early morning in both genotypes. MTsit was less responsive to electrical stimuli. The excitation threshold and the refractory period were greater in MTsit than in MTwt. After current application, APs were generated in the MTwt with 21.2 ± 2.4 mV amplitude and propagated with 5.6 ± 0.5 cm min−1 velocity. Lower intensity stimuli did not trigger APs in these plants. In MTsit APs were measured with amplitude of 26.8 ± 4.8 mV and propagated with velocity of 8.5 ± 0.1 cm min−1.
Plants possess most of the chemistry of the neuromotoric system in animals, i.e. neurotransmitter such as acetylcholine, cellular messengers like calmodulin, cellular motors, e.g. actin and myosin, voltage-gated ion channels and sensors for touch, light, gravity and temperature. Although this nerve-like cellular equipment has not reached the same great complexity as is the case in nerves, a simple neural network has been formed within the phloem, enabling it to communicate successfully over long distances. The reason why plants have developed pathways for electrical signal transmission most probably lies in the necessity to respond rapidly to environmental stress factors. Different environmental stimuli evoke specific responses in living cells which ave the capacity to transmit a signal to the responding region. In contrast to chemical signals such as hormones, electrical signals are able to rapidly transmit information over long distances. Most of the plant action potentials studied so far have a velocity in the range of 0.01 0.2 m s?1. However, in soybean, action potentials reached conduction rates of up to 30 m s?1, similar to the speed of action potentials in nerves (Volkov et al. 2000). As regards the origin of the neuronal system in plants, it appears unlikely that it was adopted from animals. In our search for the common evolutionary roots of action potentials in plants and animals, we need to look at unicellular ancestors which do not need to transmit signals over long distances. The function of electrical transmission has most probably evolved at a later evolutionary stage. The assumption is that in the course of evolution the development of plants and animals branched off into different directions. Since cellular excitability was found to exist in primitive organisms, it is obvious that both plants and animals inherited their basic neuronal capabilities from their bacterial ancestors (Simons 1992). Szmelcman and Adler (1976) observed changes in membrane potential during bacterial chemotaxis. Even the sensitivity to mechanical touch is known to be an early evolutionary achievement. Martinac et al. (1987) detected pressure-sensitive ion channels in Escherichia coli, suggesting that these channels have an osmotic function. For the early evolution of action potentials, an osmotic function can also be assumed in unicellular alga such as Acetabularia (Mummert and Gradmann 1976). A mechanosensitive ion channel was also found in the yeast plasma membrane (Gustin et al. 1988), providing convincing evidence that plants inherited mechanical sensitivity from bacterial ancestors in the course of millions of years of evolution. The characean algae, which include Chara and Nitella, are also known to be the ancestors of higher plants. Action potentials were observed in the internodal cells of Nitella in 1898 by Hrmann, who used extracellular electrodes long before they were observed in isolated nerve cells by Adrian and Bronk (1928). Characean internodal cells respond to electrical stimulation in a manner similar to the contraction response displayed by skeletal muscles following electrical stimulation by nerve cells. In characean cells, electrical stimulation causes the cessation of protoplasmic streaming which is incited by the same interactions between actin and myosin that cause contraction in muscles (Hrmann 1898). In the course of evolution, once plants had gained and settled on dry land, their excitability and neuronal capability were used to develop numerous survival tactics. For instance, one important step was the development of fast-moving stomatal guard cells in response to environmental changes, while another was the electrical communication system which uses the phloem to transmit information over long distances within the plant body (Fromm and Lautner 2005).
If biology throughout the nineteenth and twentieth centuries was dominated by the metaphor of the machine, the metaphor underlying twenty first century biology is that of the network or web. A rapid proliferation of molecular data coupled with increased computational power has revealed that gene regulation, protein interaction, the topology of metabolism and signal-transduction in and between cells, tissues, organs and organisms can all be described as robust, resilient and modular networks. Such small-world networks are characterised by rapid signal propagation, a capacity for computation and for synchronisation between the same, or different, hierarchic levels. Organelles, cells, tissues, organisms and ecosystems are not mere aggregations of components, but are hierarchies of interacting systems or modules, each possessing a degree of autonomy, and each a degree of interdependence. Into this metaphor of the network has emerged the discipline of integrative plant electrophysiology, called by its adherents, plant neurobiology. This field aims to understand how plants perceive, recall and process experience, coordinating behavioural responses via integrated information networks that include molecular, chemical and electrical levels of signalling. Integrative plant electrophysiology rejects the long standing view of plants as passive insensate automata that react to the environment with mechanical simplicity. The controversial use of the word ‘neurobiology’ as applied to plants signifies that long-distance electrical signals, such as action potentials, convey meaningful information from the site of initiation to a distant site, where the signal is interpreted and evaluated, and an adaptive behavioural response is mounted. Such inter-module communication is ‘nervous’ in the sense that it is adaptive, thereby implying capacities for memory, learning, anticipating the future and for generating novel responses. By itself a touch stimulus is meaningless, and by itself a behaviour (e.g. Mimosa leaf folding) is meaningless. Meaning lies in the network of processes that associate and integrate these events. Communication processes within, and between plants and associated organisms, can therefore be considered as biosemiotic, involving as they do the interpretation and evaluation of stimuli. This review traces historical aspects of the development of integrative plant electrophysiology and the methods that inform it, with a special emphasis on the work of Indian biophysicist Sir J. C. Bose (1858–1937), who, in an impressive body of published research, proposed that plants and animals share essentially similar fundamental physiological mechanisms. The first scientist to appreciate that responses in plants (e.g. leaf folding in the sensitive plant Mimosa) constitute behaviour reliant on integrative electrical signals; Bose argued further that all plants co-ordinate their movements and integrate their responses to the world through electrical signalling. Despite their sessile habits, plants are to be regarded as sensate, active, intelligent explorers of the world. Bose identified a fundamental physiological motif that interlinked measurable pulsations or oscillations in cellular electric potentials with oscillations in cell turgor pressure, cellular contractility and growth. All plants respond to the world and to other living things through adaptations of this pulsatile motif, an electromechanical pulse that underlies electro-osmotically enacted behaviour. J.C. Bose’s conclusions that all plants possess a nervous system, a form of intelligence, and a capacity for remembering and learning, were poorly received by prominent electrophysiologists of his time. Experiments devoted to plant responsiveness, inter-organism communication, kin-recognition, foraging, intelligence and learning as mediated by electrical signalling, are now published and debated in the mainstream literature as aspects of integrative plant electrophysiology.
p>We provide a brief definition and history of signals, pointing out how differences in body plan between plants and animals require fundamentally different signaling mechanisms, and then list the diversity of chemical and physical signals along with their pathways of transmission, providing details on molecular signals and focusing on the phloem and xylem as being the main conduits for (rapid) systemic signaling. The two major electrical (action potentials and variation potentials) as well as hydraulic signals are then described. The latter part of the chapter deals with methods of analysis of molecular signals, including accessing the phloem and identifying the array of gene products transported therein. A description is provided of the modern methods used in metabolomics and phenotyping to analyze the metabolic consequences of signal action. Conventional techniques for analyzing electrical and hydraulic signals and their ionic components using electrodes are then furnished. Finally we describe novel techniques developed recently in the animal field using fluorescence to monitor real-time changes in membrane potential, which could be adapted for plants to open up new vistas in our understanding of electrical signals in plants.</p
Translocation of photoassimilates from the source leaves to the heterotrophic parts of the plant demands three different functions executed by the phloem system. The photosynthate is collected in the source leaves (phloem loading), translocated from source to sink (phloem transport), and delivered in the sink tissues (phloem unloading). It is expected that anatomy and physiology of the particular phloem sections reflect the specific tasks to be carried out. Investigations over the past 10 years revealed a diversity of anatomical settings in sources and sinks which seem to correspond with a multiplicity of mechanisms. Several reviews and opinion papers were recently devoted to the phloem sections engaged in loading (Delrot 1987; Van Bel 1987, 1989, 1992; Gamalei 1989, 1990, 1991; Turgeon 1989; Turgeon and Beebe 1991; Van Bel and Gamalei 1991) and unloading (Murray 1987; Turgeon 1989; Patrick 1990; Oparka 1990; Wolswinkel 1990). The functioning of the transport phloem has gained much less attention, although some silent conceptual progress has been made over the past decade. Only aspects such as the photosynthate unloading from the transport phloem (Patrick 1990) and the relation between transport phloem and solute transfer through rays (Van Bel 1990) have been reviewed recently.
Long-distance communication between organs by physical and chemical signals along the phloem is an established phenomenon. For instance, action potentials effecting on distant ion channels in Mimosa pudica are well-known long-distance messengers (Lüttge et al. 2002). Propagation of electric signals may be mainly associated with the phloem pathway (e.g. Sibaoka 1969; Fromm and Eschrich 1988; Rhodes et al. 1996). In response to an action potential propagated along the sieve tubes, ion channels and possibly aquaporins are gated selectively in distant pulvinus tissues. The resulting water flux from extensor to flexor parenchyma causes downward leaf movement in Mimosa.
Electrical signals have been studied in numerous species so far. It appears that two main types of such signals occur in plants, rapid action potentials (APs) and slower variation potentials (VPs). While APs are generally evoked by non-invasive stimuli and follow the all-or-nothing principle as in neurons, VPs are mostly triggered by wounding and do not follow the all-or-nothing law. They are correlated to the stimulus strength and last longer than APs. The transmission of both, APs and VPs, occurs via the phloem over long distances and via plasmodesmata over short distances from cell to cell. Regarding physiological functions of electrical signals, numerous examples exist. They regulate rapid leaf movements in order to catch insects and for instance, affect nutrient uptake, gene expression and phloem transport. Recently, it was shown that apart from hydraulic signals, electric signals also play a significant role in root-to-shoot communication of drought-stressed plants. Re-irrigation of plants after soil drying initiates rapid hydraulic as well as electric signalling which affects the gas exchange of leaves. In addition, evidence was found for a link between electrical signals and photosynthesis as well as respiration. Wound-induced VPs cause a transient suppression in photosynthetic activity and an increase in respiratory CO2 release. The results led us to conclude that different stimulation types trigger characteristic electrical signals each with specific influence on physiological processes.
Membrane potentials of −;160 to −210 mV were recorded with microelectrodes inserted into meta-phloem sieve tubes of intact zucchini plants (Cucurbita pepo L. var. medullosa Alef.). The effects of darkness, white light and colored light on membrane potential were studied. Reference electrodes were in contact with the apoplast via fluid-filled cavities or “drinks”. Electrolyte solutions (100 mM) in the cavities could be quickly replaced by flushing with 100 mM solutions of sucrose, KCl, sorbitol, or EDTA without altering osmolarity. KCl and EDTA caused depolarization of the sieve tube membrane potential, while sucrose caused depolarization or hyperpolarization of the sieve tube membrane potential in mature or growing plant parts respectively. Recovery of the original voltage was recorded when rapid (sucrose) or slow (sorbitol) transients occurred. When two measuring circuits were installed, one in a growing fruit and the other in the petiole of the subtending mature leaf, the alteration of the sieve tube membrane potential at one site was accompanied by an alteration of the potential at the other site after a few seconds. The responses were opposite in the exporting leaf and importing fruit when sucrose was applied. The signal, transmitted via the sieve tubes, reached maximum velocities of 10 cm per second.
Electrical signaling on long and short distances exists in plants. There are three major types of electrical signaling in plants and animals: action potentials, electrotonic potentials, and graded potentials. The action potential in plants can propagate over the entire length of the cell membrane and along the conductive bundles of tissue with constant amplitude, duration, and speed. Electrotonic potentials exponentially decrease with distance. An intermediate place takes so-called graded potentials that involve the process of electrical excitation but do not evolve into full-fledged action potentials. A graded potential is an electrical signal that corresponds to the size of the stimulus. Electrical signals can propagate along the plasma membrane on short distances in plasmodesmata, and on long distances in a phloem. In this chapter, we discuss electrical signaling in the Venus flytrap and Mimosa pudica.
Long-distance transmission of signals is a critical event in the life of trees. Many physiological studies have deduced that hormone-like substances together with hy-draulic/electrical signals mediate this important function of the plant life. However the nature of the complex network of signalling in trees has remained essentially unexplored. Recent molecular and genetic studies offer new approaches to understanding the mecha-nisms underlying the transmission of signals.
J.C. Bose (1858-1937) was one of the world's first biophysicists. He was the first person to use a semi conducting crystal to detect radio waves, and the ingenious inventor of a portable apparatus for generating and detecting microwaves (~1 cm to 5 mm radio waves, frequency 12-60 GHz), as well as inventing many instruments now routinely used in microwave technology. Bose extended his specialist knowledge of the physics of electromagnetic radiation into insightful experiments on the life-processes of plants. He became a controversial figure in the west. He invented unique, delicate instruments for simultaneously measuring bioelectric potentials and for quantifying very small movements in plants. He worked with touch-sensitive plants, including Mimosa pudica, with plants that perform spontaneous movements, including the Indian telegraph plant Desmodium, and with plants and trees that did not make obvious rapid movements. Bose concluded that plants and animals have essentially the same fundamental physiological mechanisms. All plants co-ordinate their movements and responses to the environment through electrical signalling. All plants are sensitive explorers of their world, responding to it through a fundamental, pulsatile, motif involving coupled oscillations in electric potential, turgor pressure, contractility, and growth. His overall conclusion that plants have an electromechanical pulse, a nervous system, a form of intelligence, and are capable of remembering and learning, was not well received in its time. A hundred years later, concepts of plant intelligence, learning, and long-distance electrical signalling in plants have entered the mainstream literature.
The anatomical and physiological isolation of the sieve element-companion cell complex (se-cc complex) was investigated in stems of Ricinus communis L. and Salix alba L. In Ricinus, the plasmodesmatal frequencies were in the proportions 8∶1∶2∶30, in the order given, at the interfaces between sieve tube-companion cell, sieve tube-phloem parenchyma cell, companion cellphloem parenchyma cell, and phloem parenchyma cellphloem parenchyma cell. The membrane potentials of the se-cc complex and the surrounding phloem-parenchyma cells sharply contrasted: the membrane potential of the se-cc complex was about twice as negative as that of the phloem parenchyma. Lucifer Yellow CH injected into the sieve element or into the companion cell remained within the se-cc complex. Dye introduced into phloem parenchyma only moved (mostly poorly) to other phloem-parenchyma cells. The distribution of the plasmodesmatal frequencies, the differential dye-coupling and the sharp discontinuities in membrane potentials indicate that the se-cc complexes constitute symplast domains in the stem phloem. Symplastic autonomy is discussed as a basic necessity for the functioning of the se-cc complex in the stem.
Using willow plants (Salix viminalis L.) raised from cuttings, electric excitability and signal transmission were investigated extra- and intracellularly. Following root stimulation, willow plants generate action potentials that are propagated throughout the plant at velocities of 2 to 5 cm sec−1. Shifts in CO2, O2 and H2O exchange indicate the arrival of a signal in the leaves. The hydroponically grown root system is stimulated by providing nutrients, hormones or pH-changes. While the application of nutrients, auxin and cytokinins commonly leads to an increase in both CO2-uptake rate and transpiration rate, abscisic acid and acidification from pH 7.0 to pH 4.0 cause a decrease in both CO2-uptake rate and transpiration rate.
Following all applications the foliar gas exchange responded constantly after 3 min. It is calculated that this lag is too short for moving a signalling substance to the leaves via the transpiration stream. This indicates that rapidly evoked and propagated electric signals are the route whereby stimulations are transmitted.
Mimosa pudica has three distinct specialized organs, namely, pulvinus, secondary pulvinus, and pulvinule, which are respectively controlling the movements of petioles, leaflets, and pinna in response to external stimuli. Water flow is a key factor for such movements, but detailed studies on the organization of the vascular system for water transport in these organs have not been published yet. In this study, organizations of the xylem vessels and morphological features of the pulvinus, the secondary pulvinus, and the pulvinule were experimentally investigated by X-ray computed tomography and histological technique. Results showed that the xylem vessels were circularly distributed in the specialized motile organs and reorganized into distinct vascular bundles at the extremities. The number and the total cross-sectional area of the xylem vessels were increased inside the specialized motile organs. Morphological characteristics obtained in this study provided new insight to understand the functions of the vascular networks in the dynamic movements of M. pudica. Microsc. Res. Tech., 2013. © 2013 Wiley Periodicals, Inc.
Chlorine (Cl) occurs predominantly as Cl in soil and plant. It is an essential micronutrient of higher plants and participates in several physiological metabolism processes. Its functions in plant growth and development include osmotic and stomatal regulation, evolution of oxygen in photosynthesis, and disease resistance and tolerance. At adequate levels of supply, Cl improves the yields and quality of many crops such as onions and cotton if the soils are deficient in this nutrient. When excessive, Cl can be as a major component of salinity stress and toxic to plants. This paper provides a brief review of current progresses on Cl nutrition of higher plants.
From the cambial stage onwards, the symplasmic autonomy of sieve element/companion cell complexes (SE/CC-complexes) was followed in stems ofLupinus luteus L. by microinjection techniques. The membrane potential and the symplasmic autonomy of the mature SE/CC-complex was measured in successive internodes. A microelectrode was inserted into SE/CC-complexes or phloem parenchyma cells (PPs) and, after stabilization of the membrane potential, the membrane-impermeant fluorescent dye Lucifer Yellow CH (LYCH) was injected intracellullary. The plasmodesmata of the cambial SE/ CC precursor were gradually shut off at all interfaces beginning at the walls to be transformed into sieve plates. In the course of maturation, symplasmic discontinuity was maintained at the longitudinal walls of the complex. In the transverse walls of the SE, wide sieve pores were formed giving rise to longitudinal multicellular symplasmic domains of SE/CC-complexes. Symplasmic isolation of the files of mature SE/CC-complexes was demonstrated in several ways: (i) the membrane potential of the SE/CC-complexes (between -100 mV and -130 mV) was consistently more negative than that of the PPs (between-50 and -100 mV), (ii) No exchange of LYCH was observed between SE/CC-complexes and the PPs. Lucifer Yellow CH injected into the SEs exclusively moved to the associated CCs and to other SE/CC-complexes whereas LYCH injected into the PPs was only displaced to other PPs. (iii) The electrical coupling ratio between adjacent PPs was ten times higher than that between SE/CC-complex and PP. A gradient in the membrane potential of the SE/CC-complexes along the stem was not conclusively demonstrated.
This review introduces the characteristics of electrical signals in higher plants and their corresponding physiological significance, and describes in detail the impact of environmental factors (e.g. light and temperature) on the electrical potential of the plants. Also, we evaluate the measurement techniques used for electrical signals in plants, including intracellular measurement, extracellular measurement, measurement of the ion channel based on the patch-clamp technique and on the non-invasive microelectrode vibrating probe technique. We also give a brief review of the applications of these methods for investigating electrical signals in plants. The ionic mechanism of electrical activity in plants is then discussed in terms of environmental response in higher plants, and this is used to provide a theoretical basis for quantitative description of the electrical signals in plants. A model for interpretation of the electrical signal mechanisms in higher plants is discussed, but further experiments are required for the verification of this model.
Aminoacidandsucrose contents wereanalyzed inthechlo- roplastic, cytosolic, andvacuolar compartments andinthe phloemsapofilluminated spinach leaves (Spinacia oleracea L.). Thedetermination ofsubcellular metabolite distribution wascar- riedoutbynonaqueous fractionation offrozen andlyophilized leafmaterial usinga novelthree-compartment calculation method. Thephloemsapwascollected byaphidstylets which hadbeensevered byalaser beam.Subcellular analysis revealed thattheaminoacidsfoundinleaves arelocated mainly inthe chloroplast stromaandinthecytosol, thesumoftheir concentra- tions amounting to151and121millimolar, respectively, whereas theaminoacidconcentrations inthevacuole areoneorderof magnitude lower. Theaminoacidconcentrations inthephloem saparefound tobenotverydifferent fromthecytosolic concen- trations, whereas thesieve tubeconcentration ofsucrose isfound tobeoneorderofmagnitude higher thaninthecytosol. Itis concluded thatthephloemloading results ina preferential ex- traction ofsucrose fromthesourcecells.
In recent years, the effect of heat-induced electrical signalling on plant photosynthetic activity has been demonstrated for many plant species. However, the underlying triggers of the resulting transient inhibition of photosynthesis still remain unknown. To further investigate on this phenomenon, we focused in our present study on soybean (Glycine max L.) on the direct effect of signal transmission in the leaf mesophyll on conductance for CO(2) diffusion in the mesophyll (g(m) ) and detected a drastic decline in g(m) following the electrical signal, whereas the photosynthetic electron transport rate (ETR) was only marginally affected. In accordance with the drop in net photosynthesis (A(N) ), energy dispersive X-ray analysis (EDXA) revealed a shift of K, Mg, O and P on leaf chloroplasts. Control experiments under elevated CO(2) conditions proved the transient reduction of A(N) , ETR, the chloroplast CO(2) concentration (C(c) ) and g(m) to be independent of the external CO(2) regime, whereas the effect of the electrical signal on stomatal conductance for CO(2) (g(s) ) turned out much less distinctive. We therefore conclude that the effect of electrical signalling on photosynthesis in soybean is triggered by its immediate effects on g(m) .
Introduction Plant Mechanoresponses General Principles of Touch Perception Signal Transduction in Touch and Gravity Perception Insights from Transcriptional Profiling Interaction of Touch and Gravity Signaling/Response Conclusion and Perspectives Acknowledgments Literature Cited
Summary • In the sensitive species Mimosa pudica electric signals arise when the leaves are stimulated by touching or wounding. Experiments reported here provide informa- tion about a photosynthetic response that results from heat-induced electrical sig- nalling in leaves. • Electric potential measurements, combined with chlorophyll fluorescence, as well as gas exchange measurements showed that wounding evokes an electrical signal that travels rapidly into the neighbouring leaf pinna to eliminate the net-CO 2 uptake rate. At the same time the PSII quantum yield of electron transport is reduced from c . 0.6 to 0.2. Two-dimensional imaging analysis of the chlorophyll fluorescence signal revealed that the yield reduction spreads acropetally through the pinna and via the veins through the leaflets. •T o determine the speed of a chemical signal, a part of a pinna was exposed to 14 CO 2 . The remaining parts of the leaf were provided with label only when the translocation was extended to 12 h, indicating that a chemical signal is much too slow to account for the photosynthetic response after heat stimulation. • The results provide evidence for a role of the electrical signal in the regulation of photosynthesis because the high speed of the signal transduction rules out the involvement of a chemical signal, and the photosynthetic response occurs after the arrival of the electrical signal in the leaf pinna.
In the sensitive plant, Mimosa pudica, action potentials arise when the leaves are touched and they trigger a sudden decrease in turgor of the pulvinar motor cells, which causes the leaf to close. These potentials may travel through the phloem and they appear to influence pulvinar phloem unloading after stimulation. Mature leaves were exposed to 14CO2 and phloem translocation was observed by autoradiography. In unstimulated pulvini, labeled photoassimilates were restricted to the phloem. However, after stimulation, the 14C-label appeared to be concentrated in the extensor region of the motor cortex. Since stimulation elicits an action potential, it is suggested that it also triggers phloem unloading of sucrose in the pulvini.
In search of a K+ channel involved in phloem transport we screened a Vicia faba cotyledon cDNA library taking advantage of a set of degenerated primers, flanking regions conserved among K+ uptake channels. We cloned VFK1 (for Vicia faba K+ channel 1) characterised by a structure known from the Shaker family of plant K+ channels. When co-expressed with a KAT1 mutant in Xenopus oocytes, heteromers revealed the biophysical properties of a K+ selective, proton-blocked channel. Northern blot analyses showed high levels of expression in cotyledons, flowers, stem and leaves. Using in situ PCR techniques we could localise the K+ channel mRNA in the phloem. In the stem VFK1 expression levels were higher in the lower internodes. There channel transcripts increased in the light and thus under conditions of increased photosynthate allocation. VFK1 transcripts are elevated in sink leaves, and rise in source leaves during the experimental transition into sinks. Fructose- rather than sucrose- or glucose-feeding via the petiole induced VFK1 gene activity. We therefore monitored the fructose sensitivity of the sieve tube potential through cut aphid stylets. In response to an 1 h fructose treatment the sieve tube potential shift increased from 19 mV to 53 mV per 10-fold change in K+ concentration. Under these conditions K+ channels dominated the electrical properties of the plasma membrane. Based on the phloem localisation and expression patterns of VFK1 we conclude that this K+ channel is involved in sugar unloading and K+ retrieval.
A method for determining the subcellular metabolite levels in spinach protoplasts is described. The protoplasts are disrupted by centrifugation through a nylon net, releasing intact chloroplasts which pass through a layer of silicone oil into perchloric acid while the remaining cytoplasmic components remain over the oil and are simultaneously quenched as acid is centrifuged into them. Cross-contamination is measured and corrected for using ribulose 1,5-bisphosphate as a chloroplastic marker and phosphoenolpyruvate carboxylase as a cytoplasmic marker. A method for separation of intact protoplasts from the medium by silicone oil centrifugation is described, which allows a correction to be made for the effect of free chloroplasts and broken protoplasts. Methods for inhibiting chloroplast photosynthesis, without inhibiting protoplasts, are presented. It is demonstrated that ribulose 1,5-bisphosphate, ATP, ADP, AMP, inorganic phosphate, hexose phosphate, triose phosphate, fructose 1,6-bisphosphate, and 3-phosphoglycerate can be reliably recovered in the subcellular fractions isolated from protoplasts, and measured by enzymic substrate analysis.
A procedure is described for the measurement of the sieve tube membrane potential in the phloem of bark strips from Salix exigua Nutt. Measurements were made by inserting a measuring microelectrode into sap exuding from severed stylets of the willow aphid, Tuberolachnus salignus. Data taken from 20 bark strips gave an average potential of -155 +/- 9 millivolts. Evidence is presented for an electrogenic component of the sieve tube membrane potential. The occurrence of a saturable sucrose-induced membrane depolarization is consistent with the concept of sugar accumulation by a sucrose/H(+) co-transport mechanism.
The rate of O2 uptake by excised Samanea pulvini oscillates with a circadian rhythm during 52 hours of darkness. Rates of respiration increase during pulvinar opening and decrease prior to and during closure, consistent with the concept that opening requires a greater expenditure of energy. Externally supplied sucrose, necessary for perpetuation of the leaflet movement rhythm, has a small promotive effect on the rate of respiration.
Potassium flux into and out of pulvinal motor cells is the basis for the turgor changes leading to leaflet movement in Albizzia and other nyctinastic plants. Endogenous rhythm, phytochrome and a blue absorbing pigment interact to control this movement, apparently by regulating potassium pumps and diffusion channels in motor cell membranes.
Mature leaves of Mimosa pudica L. or parts of them were exposed to 14CO2, and translocation was recorded by macroautoradiography. It was observed that considerable amounts of labelled photoassimilates were accumulated in pulvini when the leaf was stimulated. In non-stimulated leaves, no such accumulation of label was observed.
Microautoradiographs of pulvinar regions of the non-stimulated leaf showed 14C- label restricted to the phloem. When stimulated, the 14C- label was unloaded from the phloem of the pulvini. Labelled photoassimilates appeared most concentrated in the walls of the collenchymatous cells and beyond in the extensor region of the motor cortex. There, label was accumulated in the apoplastic compartments. Stimulation causes a sudden phloem unloading of sucrose, and its accumulation in the apoplast lowers the water potential which eventually exceeds the osmotic potential of the extensor cells of the motor cortex. By removal of cytoplasmic water the motor cells lose turgidity which results in the closing movement of the leaflets, and — some seconds later — in the bending down of the petiole. In late afternoon night-stimulation triggers sucrose unloading in secondary pulvini. During phases of relaxation, labelled material is taken up by motor cells of the extensor, which concomitantly gain turgor.
Penetration of leaves of barley,Hordeum vulgare L., by the corn leaf aphid,Rhopalosiphum maidis (Fitch), was studied with light, phase, and electron microscopes. Penetration of epidermis and mesophyll was largely intercellular, that of vascular bundles or veins largely intracellular. Like other aphids,R. maidis secretes a salivary sheath which surrounds the stylets. When mesophyll cells and parenchymatous elements of the veins were penetrated by stylets, their protoplasts were pushed to one side by intruding sheath material; hence, the protoplasts were not punctured by the stylets, although sometimes the plasmalemma of penetrated cells was ruptured by sheath material. The salivary sheaths ended more or less abruptly outside the walls of sieve elements being fed upon, the maxillary stylets projecting beyond the sheaths and into the sieve elements. Before penetrating a functional sieve element the aphid apparently flushes its stylets in order to clear them for ingestion of food. Salivary and food canals merge near the tips of the maxillary stylets to form a single canal, which ends short of the tips.
Eine Untersuchung des Temperatureinflusses auf die endogene Tagesrhythmik beiPhaseolus (untersucht an den tagesperiodischen Bewegungen) ergab:1.
Bei niedriger Temperaturkann eine Abkrzung der Periodenlngen um mehrere Stunden eintreten. So betrgt die Periodenlnge unter den gewhlten Versuchsbedingungen bei 22 27,5 Std, bei 14,5 23,2 Std.
2.
Bei Temperaturen von etwa 10 versagt der Mechanismus der endogenen Tagesrhythmik. Es treten ohne einen bergang zu den annhernd tagesperiodischen Schwingungen Perioden mit Lngen von 8–18 Std auf. Bei einer Rckbertragung in hhere Temperaturen wird die endogene Tagesrhythmik wieder deutlich.
3.
Im 12:12stndigen Licht-Dunkel-Wechsel treten auch bei den extrem niedrigen Temperaturen (z. B. bei 10) tagesperiodische Bewegungen auf. Whrend bei mittleren Temperaturen ein Licht-Dunkel-Wechsel nur dann synchrone Bewegungen induziert, wenn er vom tagesperiodischen Licht-Dunkel-Wechsel nicht stark abweicht, sind bei Temperaturen um 10 synchrone Bewegungen auch im 66, zum Teil sogar im 33 Std Licht-Dunkel-Wechsel mglich. Auch bei 15 ist die grere Plastizitt teilweise schon erkennbar.
4.
Im Temperaturbereich von etwa 11–30 scheint die durch Blatthebung gekennzeichnete Phase der endogenen, Tagesrhythmik bei einer Temperaturerhhung verlngert, bei einer Temperatursenkung verkrzt zu werden. Die andere Phase der endogenen Rhythmik scheint auf die Temperatur gerade entgegengesetzt zu reagieren.
Concentrations of AMP, ADP, ATP, and inorganic phosphate (Pi) were determined in buds of five deciduous tree species (Acer pseudoplatanus, Alnus glutinosa, Fagus sylvatica, Fraxinus excelsior, Quercus robur) during spring reactivation from February to the middle of May. In closed buds of diffuse-porous wood trees (Acer, Alnus, Fagus), the content of adenine nucleotides (AdN) increased temporarily between the middle of February and the middle of March. The main increase of AdN concentration appeared either when buds became swollen (Fraxinus, Fagus, Quercus), or at the time of bud-break (Acer, Alnus). Pi content in general decreased during the course of reactivation. It was almost zero in buds of Quercus at bud-break and afterwards, but in Fraxinus Pi concentration rose when bud-break took place. The extremely low AdN content in Quercus buds is contrasted by a steep increase in AdN content in Fraxinus following bud-break. The decrease of AdN content in emerging leaves of Quercus and Fagus could be related to the high age of these trees.
By inserting microelectrodes into cells of various tissues, it was shown that elongated parenchyma cells in the phloem and protoxylem, which have larger membrane potential than inexcitable cells of other types, generate action potentials with conduction. The electrical features of these cells are essentially similar to those of nerve and muscle cells.
The rate of O(2) uptake by excised Samanea pulvini oscillates with a circadian rhythm during 52 hours of darkness. Rates of respiration increase during pulvinar opening and decrease prior to and during closure, consistent with the concept that opening requires a greater expenditure of energy. Externally supplied sucrose, necessary for perpetuation of the leaflet movement rhythm, has a small promotive effect on the rate of respiration.
Events of reactivation by re-illumination were studied in predarkened detached mature maize leaves, which were arranged as distal sources and proximal sinks; the latter were kept in CO(2)-free atmosphere and were either illuminated or darkened. Adenine nucleotide (AdN) content and orthophosphate (Pi) concentrations were measured 10 minutes, 30 minutes, and 2, 7, and 14 hours after the onset of re-illumination. For comparison, mature leaves attached to the plant were analyzed.The sum of AdN increased up to 7 hours of re-illumination, then dark sinks and their sources showed decreasing amounts of AdN, while the increase continued up to 14 hours in sources and illuminated sinks. In leaves attached to the plant, no further increase in AdN level followed the 7-hour mark. The amount of individual AdN (ATP, ADP, AMP) differed considerably in sources and sinks of the detached leaves. Although both the source supplying the illuminated sink and the source supplying the dark sink were treated the same, they showed striking differences in AdN contents. Such relations were also observed, when ATP/ADP ratios and Pi concentrations were compared. The influence a sink can exert on its source suggests a participation of the physiological events in the sink on the regulation of AdN and Pi metabolism in the source.
with collaboration of Homlenskite IV (1964) Participation of ATP in the motor function of the Mimosa pudica leaf
- MN Lyubimova
Fedorovich IB, with collaboration of Homlenskite IV (1964) Participation of ATP in the motor function of the Mimosa pudica leaf
- M N Lyubimova
- N S Demyanovskaya
- MN Lyubimova