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PubMedDate not supplied

Phase response curve for the ultradian rhythm of the lateral leaflets of Desmodium gyrans using DC current pulses.

In the present study the leaf movement rhythm was perturbed by the application of DC current pulses (15 microA, 10 seconds, voltage applied: 10 V) to the upper part of the pulvinus, passing through the pulvinus and its stalk. The pulses were applied at four different positions of the leaflets: when the leaves were at the lowermost position, when moving up, at the uppermost position and when moving down. The pre-perturbed and the post-perturbed rhythms were compared. We found that the rhythms were shifted in phase and the phase shifts observed at the four different positions of the leaflets were significantly different in magnitude as well as direction. Furthermore, we could also observe phase advances, which is in contrast to an earlier finding. A phase response curve (PRC) was constructed to illustrate the sensitivity of the oscillating leaflet system to DC pulses. Substantial delays of about 50 s (as compared to the period of about 200 s) were obtained when pulses were administered at the lowermost position and when leaflet were moving upwards, while advances or no phase shifts were recorded in the uppermost position and when leaflet were moving down respectively.

Activity Cycles↗

PubMed2001

Structures of the preantennal region of several species of Damalinia (Phthiraptera: Trichodectidae).

A comparative study was made of the structures of the preantennal region of nine species of Damalinia Mjöberg, 1910 (Phthiraptera: Trichodectidae). Variability in the form of the head, ventral carina, pulvinus, mandibles, and labrum was observed by light and scanning electron microscopy. According to previous studies, the form of the head is possibly influenced by the density and texture of the hair of the host. The ventral carina, which maybe sharp or blunt, and the pulvinus, a membranous lobe, of these parasite species of different hosts, were studied. Photographs of the mandibles and labrum show a high variability according to species.

Animals↗

PubMed1985

Osmotica, dimethyl sulfoxide, parahydroxymercuribenzoate, and cyanide change the period of the circadian clock in the pulvini of Phaseolus coccineus L.

Several substances change the period length of the circadian oscillator in the laminar pulvinus of Phaseolus coccineus L. if offered continuously via the transpiration stream to the isolated leaves in continuous light and constant temperature. The osmotica mannitol and PEG 6000 (polyethylene glycol) lengthen the circadian period from 27.9 hr (control) to about 29.5 hr. The dose-response of both substances reveal saturation curves. DMSO (dimethyl sulfoxide) lengthens the circadian period much more strongly than the osmotica. The dose-response curve reflects a curvilinear dependence of the period length from the DMSO concentration. PHMB (p-hydroxymercuribenzoate) and NaCN shorten the circadian period. The dose-response curve for PHMB is a saturation curve; saturation is reached at 80 microM PHMB with a period length of about 25.7 hr. We conclude from these results that the period of the circadian oscillator in the Phaseolus pulvinus is not directly homeostatically regulated but influenced by the intracellular milieu which can be changed by affecting membrane permeability, active transport systems or other regulatory systems within the cells.

Biological Clocks↗

PubMed1994

Protoplasts from Phaseolus coccineus L. pulvinar motor cells show circadian volume oscillations.

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.

Circadian Rhythm↗

PubMed1996

Inositol 1,4,5-trisphosphate may mediate closure of K+ channels by light and darkness in Samanea saman motor cells.

Leaflet movements of Samanea saman (Jacq.) Merr. depend in part upon circadian-rhythmic, light-regulated K+ fluxes across the plasma membranes of extensor and flexor cells in opposing regions of the leaf-moving organ, the pulvinus. We previously showed that blue light appears to close open K+ channels in flexor protoplasts during the dark period (subjective night) (Kim et al., 1992, Plant Physiol 99; 1532-1539). In contrast, transfer to darkness apparently closes open K+ channels in extensor protoplasts during the light period (subjective day) (Kim et al., 1993, Science 260; 960-962). We now report that both these channel-closing stimuli increase inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] levels in the appropriate protoplasts. If extensor cells are given a pulse of red light followed by transfer to darkness, channels still apparently close (Kim et al., 1993) but changes in Ins(1,4,5)P3 levels are complex with an initial decrease under red light followed by accumulation. Neomycin, an inhibitor of polyphosphoinositide hydrolysis, inhibits both blue-light-induced Ins(1,4,5)P3 production and K(+)-channel closure in flexor protoplasts and both dark-induced Ins(1,4,5)P3 production and K+ channel closure in extensor protoplasts. The G-protein activator, mastoparan, mimics blue light and darkness in that it both increases Ins(1,4,5)P3 levels and closes K+ channels in the appropriate cell type at the appropriate time. These results indicate that phospholipase C-catalyzed hydrolysis of phosphoinositides, possibly activated by a G protein, is an early step in the signal-transduction pathway by which blue light and darkness close K+ channels in S. saman pulvinar cells.

Darkness↗

PubMed2001

Auxin- and abscisic acid-dependent osmoregulation in protoplasts of Phaseolus vulgaris pulvini.

Protoplasts isolated from the laminar pulvinus of Phaseolus vulgaris and bathed in a medium containing KCl as the major salt were found to swell in response to IAA and to shrink in response to ABA. The protoplasts of flexor cells and those of extensor cells responded similarly. The results indicate that the cellular content of osmotic solutes is enhanced by IAA and reduced by ABA. The IAA-induced swelling was abolished when either the K(+) or the Cl(-) of the bathing medium was replaced by an impermeant ion or when the medium was adjusted to neutral pH (instead of pH 6). The response was inhibited by vanadate. It is concluded that the swelling is caused by enhanced influxes of K(+) and Cl(-), which probably occur through K(+) channels and Cl(-)/H(+) symporters, respectively. The ABA-induced shrinking was inhibited by 5-nitro-2-(3-phenylpropylamino)-benzoic acid, an anion-channel inhibitor, suggesting that it is caused by Cl(-) efflux through anion channels and charge-balancing K(+) efflux through outward-rectifying K(+) channels. It appears that the two plant hormones act on pulvinar motor cells to regulate their turgor pressure, as they do in stomatal guard cells. The findings are discussed in relation to the pulvinar movements induced by environmental stimuli.

Abscisic Acid↗

PubMed1995

Hormonal and gravitropic specificity in the regulation of growth and cell wall synthesis in pulvini and internodes from shoots of Avena sativa L. (oat).

Segments can be cut from the peduncular-1 internode of oat (Avena sativa L.) shoots so as to contain the graviresponsive leaf-sheath pulvinus and gibberellin-sensitive internodal tissue. Incorporation of [14C]glucose was used to monitor cell wall synthesis in these two tissues as affected by gravistimulus, indoleacetic acid (IAA), gibberellic acid (GA3), and fusicoccin (FC). Pulvinar cell wall synthesis was promoted by IAA and FC (both within about 1 h), as well as by gravistimulus (starting between 3 and 6 h), whereas GA3 had no effect on nongravistimulated pulvini. In contrast, GA3 and FC promoted internodal cell wall synthesis (initiated between 1 and 2 h), whereas IAA and gravistimulus caused a decrease in internodal uptake. FC preferentially promoted incorporation into the matrix component of the wall in both tissues. Gravistimulus failed to increase responsiveness of pulvinar tissue to IAA, whereas GA3 partially overcame gravistimulus-promoted incorporation into pulvinar cell wall, probably because of preferential movement of label into the rapidly elongating internode. The results demonstrate that these eight stimulus/tissue combinations can be examined easily in an isolated 10-mm stem segment, providing new opportunities for the comparative study of tissue- and stimulus-specific events in gene regulation and signal transduction in agronomically important cereals.

Avena↗

PubMed2001

Cytoplasmic pH dynamics in maize pulvinal cells induced by gravity vector changes.

In maize (Zea mays) and other grasses, changes in orientation of stems are perceived by pulvinal tissue, which responds to the stimulus by differential growth resulting in upward bending of the stem. The amyloplast-containing bundle sheath cells are the sites of gravity perception, although the initial steps of gravity perception and transmission remain unclear. In columella cells of Arabidopsis roots, we previously found that cytoplasmic pH (pH(c)) is a mediator in early gravitropic signaling (A.C. Scott, N.S. Allen [1999] Plant Physiol 121: 1291-1298). The question arises whether pH(c) has a more general role in signaling gravity vector changes. Using confocal ratiometric imaging and the fluorescent pH indicator carboxy seminaphtorhodafluor acetoxymethyl ester acetate, we measured pH(c) in the cells composing the maize pulvinus. When stem slices were gravistimulated and imaged on a horizontally mounted confocal microscope, pH(c) changes were only apparent within the bundle sheath cells, and not in the parenchyma cells. After turning, cytoplasmic acidification was observed at the sides of the cells, whereas the cytoplasm at the base of the cells where plastids slowly accumulated became more basic. These changes were most apparent in cells exhibiting net amyloplast sedimentation. Parenchyma cells and isolated bundle sheath cells did not show any gravity-induced pH(c) changes although all cell types responded to external stimuli in the predicted way: Propionic acid and auxin treatments induced acidification, whereas raising the external pH caused alkalinization. The results suggest that pH(c) has an important role in the early signaling pathways of maize stem gravitropism.

Cytoplasm↗

PubMed1993

Plasmalemmal, voltage-dependent ionic currents from excitable pulvinar motor cells of Mimosa pudica.

Plasmalemmal ionic currents from excitable motor cells of the primary pulvinus of Mimosa pudica were investigated by patch-clamp techniques. In almost all of the enzymatically isolated protoplasts, a delayed rectifier potassium current was activated by depolarization, while no currents were detected upon hyperpolarization. This sustained outward current was reversibly blocked by Ba and TEA and serves to repolarize the membrane potential. Outward single channel currents that very likely underly the macroscopic outward potassium current had an elementary conductance of approximately 20 pS. In addition, in a few protoplasts held at hyperpolarized potentials, depolarization-activated transient inward currents were observed, and under current clamp, action potential-like responses were triggered by depolarizing current injections or by mechanical perturbations. The activation characteristics of both inward currents and spikes showed striking similarities compared to those of action potentials in situ.

Barium↗

PubMed1996

Increased resistance to extracellular cation block by mutation of the pore domain of the Arabidopsis inward-rectifying K+ channel KAT1.

Inward-rectifying potassium channels in plant cells provide important mechanisms for low-affinity K+ uptake and membrane potential control in specific cell types, including guard cells, pulvinus cells, aleurone cells and root hair cells. K+ channel blockers are potent tools for studying the physiological functions and structural properties of K+ channels. In the present study the structural and biophysical mechanisms of Cs+ and TEA+ block of a cloned Arabidopsis inward-rectifying K+ channel (KAT1) were analyzed. Effects of the channel blockers Cs+ and TEA+ were characterized both extracellularly and intracellularly. Both external Cs+ and TEA+ block KAT1 currents. A mutant of KAT1 ("m2KAT1"; H267T, E269V) was produced by site-directed mutagenesis of two amino acid residues in the C-terminal portion of the putative pore (P) domain. This mutant channel was blocked less by external Cs+ and TEA+ than the wild-type K+ channel. Internal TEA+ and Cs+ did not significantly block either m2KAT1 or KAT1 channels. Other properties, such as cation selectivity, voltage-dependence and proton activation did not show large changes between m2KAT1 and KAT1, demonstrating the specificity of the introduced mutations. These data suggest that the amino acid positions mutated in the inward-rectifying K+ channel, KAT1, are accessible to external blockers and may be located on the external side of the membrane, as has been suggested for outward-rectifying K+ channels.

Amino Acid Sequence↗

PubMed1997

Analyses of phosphoenolpyruvate carboxylase gene structure and expression in alfalfa nodules.

Phosphoenolpyruvate carboxylase (PEPC) plays a crucial role in the assimilation of CO2 during symbiotic N2 fixation in legume root nodules. In this study, an alfalfa PEPC gene (PEPC-7), whose transcripts are found at elevated levels in nodules relative to either leaves or roots, has been isolated and characterized. The intron/exon structure of this gene is identical to that of most other plant PEPC genes except for the presence of an additional intron in the 5' untranslated region. In situ RNA hybridization studies showed that PEPC transcripts were present in the nodule meristem, the infection zone, the nitrogen-fixing zone, and the parenchyma. PEPC transcripts were also found in vascular tissue of roots and nodules and in the pulvinus of petioles. In transgenic alfalfa, a chimeric reporter gene was expressed in these same regions except that little expression was found in the nodule meristem. Analyses of promoter deletions suggest that the region between -634 and -536 is of particular importance in directing transcriptional activity to the infected zone of nodules. Within this region is a mirror repeat sequence that is potentially capable of forming an H-DNA structure. These results indicate that PEPC-7 has a central role in nitrogen-fixing nodules and that regulation of transcription is an important determinant of its activity.

Base Sequence↗

PubMed1974

Potassium flux and leaf movement in Samanea saman. I. Rhythmic movement.

Samanea leaflets usually open in white light and fold together when darkened, but also open and dose with a circadian rhythm during prolonged darkness. Leaflet movement results from differential changes in the turgor and shape of motor cells on opposite sides of the pulvinus; extensor cells expand during opening and shrink during closure, while flexor cells shrink during opening and expand during closure but change shape more than size. Potassium in both open and closed pulvini is about 0.4 N. Flame photometric and electron microprobe analyses reveal that rhythmic and light-regulated postassium flux is the basis for pulvinar turgor movements. Rhythmic potassium flux during darkness in motor cells in the extensor region involves alternating predominance of inwardly directed ion pumps and leakage outward through diffusion channels, each lasting ca 12 h. White light affects the system by activating outwardly directed K(+) pumps in motor cells in the flexor region.

Biological Transport, Active↗

PubMed1994

Control of Paraheliotropism in Two Phaseolus Species.

Paraheliotropic (light-avoiding) leaf movements have been associated with high light intensity, high temperature, and drought. We investigated leaf elevation for intact plants, pulvinus bending for excised motor organs, and size change for protoplasts from motor tissue for two Phaseolus species: Phaseolus acutifolius A. Gray, native to hot, arid regions, and Phaseolus vulgaris L., the common bean. Leaf angles above horizontal were measured for central trifoliolate leaflets of intact plants at 24, 27, and 30[deg]C at 500 and 750 [mu]mol photons (400-700 nm) m-2 s-1 over a range of water potentials; equivalent angles were determined for excised motor organs under similar conditions. Diameters were measured for protoplasts from abaxial and adaxial motor tissue over a range of photon flux density values, temperatures, and water potentials. In general, higher photon flux density and temperature resulted in elevation of leaves, bending of excised pulvini, and equivalent changes in protoplast volume (swelling of abaxial protoplasts and shrinking of adaxial protoplasts). In intact plants, lower water potentials yielded greater paraheliotropism; abaxial protoplasts increased in size, whereas adaxial ones did not change. P. acutifolius typically exhibited greater paraheliotropism than did P. vulgaris under the same conditions, a set of physiological responses likely to be highly adaptive in its native arid habitat.

Journal Article↗

PubMed1997

Increased Expression of Vacuolar Aquaporin and H+-ATPase Related to Motor Cell Function in Mimosa pudica L.

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.

Journal Article↗

PubMed1998

Transdifferentiation of mature cortical cells to functional abscission cells in bean

Abscission explants of bean (Phaseolus vulgaris L.) were treated with ethylene to induce cell separation at the primary abscission zone. After several days of further incubation of the remaining petiole in endogenously produced ethylene, the distal two-thirds of the petiole became senescent, and the remaining (proximal) portion stayed green. Cell-to-cell separation (secondary abscission) takes place precisely at the interface between the senescing yellow and the enlarging green cells. The expression of the abscission-associated isoform of beta-1,4-glucanhydrolase, the activation of the Golgi apparatus, and enhanced vesicle formation occurred only in the enlarging cortical cells on the green side. These changes were indistinguishable from those that occur in normal abscission cells and confirm the conversion of the cortical cells to abscission-type cells. Secondary abscission cells were also induced by applying auxin to the exposed primary abscission surface after the pulvinus was shed, provided ethylene was added. Then, the orientation of development of green and yellow tissue was reversed; the distal tissue remained green and the proximal tissue yellowed. Nevertheless, separation still occurred at the junction between green and yellow cells and, again, it was one to two cell layers of the green side that enlarged and separated from their senescing neighbors. Evaluation of Feulgen-stained tissue establishes that, although nuclear changes occur, the conversion of the cortical cell to an abscission zone cell is a true transdifferentiation event, occurring in the absence of cell division.

Journal Article↗

PubMed1966

Transport of the Auxin 2,4-Dichlorophenoxyacetic Acid Through Absiccion Zones, Pulvini, and Petioles of Phaseolus vulgaris.

Measurements were made of the transport of 2,4-dichlorophenoxyacetic acid-(14)C (2,4-D) through segments cut from the region of the distal abscission zone in young and old primary leaves of Phaseolus vulgaris L. When old leaves were used basipetal transport of 2,4-D in segments including pulvinar tissue, abscission zone, and petiolar tissue was much less than in wholly petiolar segments. In both young and old plants, segments consisting entirely of pulvinar tissue transported 2,4-D basipetally at a velocity about half that in petiolar tissue. At both ages the flux of 2,4-D through pulvinar tissue was less than that through petiolar tissue. In segments from old leaves the flux through pulvinar tissue was much less than in young plants; the flux through petiolar tissue changed little with age. There was no change with age in the velocity of basipetal transport. The distribution of (14)C along segments including the abscission zone showed no marked discontinuity. It was concluded that the pulvinus limited the basipetal movement of 2,4-D through segments from old leaves which included both pulvinar and petiolar tissue, but there was no evidence that the abscission zone itself was a barrier to auxin transport.

Journal Article↗

PubMed1967

Abscission: the role of aging.

Excision of Phaseolus vulgaris L. c.v. Red Kidney abscission zone explants results in senescence, mobilization, and abscission. Because these processes take place at about the same time, there has been some question as to whether they are causally related or are occurring in an independent but simultaneous fashion. Data presented here suggest that the latter interpretation is correct. After abscission zone explants are isolated from the leaf an aging process is set into motion and a degradation of metabolites in the pulvinus takes place. During the aging process the explants also become increasingly sensitive to ethylene which in turn promotes cell separation. Indoleacetic acid, cytokinins, and coumarin appear to retard aging since both degradative processes and abscission are inhibited. However, ethylene increased abscission without increasing degradative processes indicating that abscission and senescence are independent processes occurring at the same time.

Journal Article↗

PubMed1975

Contractile Characteristics of Mimosa pudica L.

The force-velocity characteristics of the primary pulvinus of Mimosa pudica have been determined using a new polytonic measurement technique. The contractile characteristics were determined from a modified form of Hill's equation (Hill, A. V. 1938. Proc. Roy. Soc. London B126: 136-195) describing the physiological contractile behavior of animal muscle. The values of the resulting Hill's constants were found to be remarkably similar to those of intact animal muscle and reconstituted contractile collagen.

Journal Article↗