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  • 11
    Electronic Resource
    Electronic Resource
    Induction and ionic basis of slow wave potentials in seedlings of Pisum sativum L. (1996)
    Springer
    Planta 200 (1996), S. 416-425 
    Details
    ISSN: 1432-2048
    Keywords: Apoplastic pH ; Cell input resistance ; Membrane potential ; pH indicator (DM-NERF) ; Pisum sativum ; Slow wave potential ; Surface potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Slow wave potentials (SWPs) are transient depolarizations which propagate substantial distances from their point of origin. They were induced in the epidermal cells of pea epicotyls by injurious methods such as root excision and heat treatment, as well as by externally applied, defined steps in xylem pressure (Px)at in the absence of wounding. The common principle of induction was a rapid increase in Px. Such a stimulus appeared under natural conditions after (i) bending of the epicotyl, (ii) wounding of the epidermis, (iii) rewatering of dehydrated roots, and (iv) embolism. The induced depolarization was not associated with a change in cell input resistance. This result and the ineffectiveness of ion channel blockers point to H+-pumps rather than ion channels as the ionic basis of the SWP. Stimuli such as excision, heat treatment and pressure steps, which generate SWPs, caused a transient increase in the fluorescence intensity of epicotyls loaded with the pH-indicator DM-NERF, a 2′, 7′-dimethyl derivative of rhodol, but not of those loaded with the pH indicator 2′,7′-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF). Matching kinetics of depolarization and pH response identify a transient inactivation of proton pumps in the plasma membrane as the causal mechanism of the SWP. Feeding pump inhibitors to the cut surface of excised epicotyls failed to chemically simulate a SWP; cyanide, azide and 2,4-dinitrophenol caused sustained, local depolarizations which did not propagate. Of all tested substances, only sodium cholate caused a transient and propagating depolarization whose arrival in the growing region of the epicotyl coincided with a transient growth rate reduction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231397
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  • 12
    Electronic Resource
    Electronic Resource
    Wall relaxation in growing stems: comparison of four species and assessment of measurement techniques (1987)
    Springer
    Planta 171 (1987), S. 266-278 
    Details
    ISSN: 1432-2048
    Keywords: Cell expansion ; Cell wall relaxation ; Growth (stems) ; Stem growth ; Turgor pressure ; Wall loosening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This study was carried out to develop improved methods for measuring in-vivo stress relaxation of growing tissues and to compare relaxation in the stems of four different species. When water uptake by growing tissue is prevented, in-vivo stress relaxation occurs because continued wall loosening reduces wall stress and cell turgor pressure. With this procedure one may measure the yield threshold for growth (Y), the turgor pressure in excess of the yield threshold (P-Y), and the physiological wall extensibility (ϕ). Three relaxation techniques proved useful: “turgor-relaxation”, “balance-pressure” and “pressure-block”. In the turgor-relaxation method, water is withheld from growing tissue and the reduction in turgor is measured directly with the pressure probe. This technique give absolute values for P and Y, but requires tissue excision. In the balance-pressure technique, the excised growing region is sealed in a pressure chamber, and the subsequent reduction in water potential is measured as the applied pressure needed to return xylem sap to the cut surface. This method is simple, but only measures (P-Y) not the individual values of P and Y. In the pressure-block technique, the growing tissue is sealed into a pressure chamber, growth is monitored continuously, and just sufficient pressure is applied to the chamber to block growth. The method gives high-resolution kinetics of relaxation and does not require tissue excision, but only measures (P-Y). The three methods gave similar results when applied to the growing stems of pea (Pisum sativum L.), cucumber (Cucumis sativus L.), soybean (Glycine max (L.) Merr.) and zucchini (Curcubita pepo L.) seedlings. Values for (P-Y) averaged between 1.4 and 2.7 bar, depending on species. Yield thresholds averaged between 1.3 and 3.0 bar. Compared with the other methods, relaxation by pressure-block was faster and exhibited dynamic changes in wall-yielding properties. The two pressure-chamber methods were also used to measure the internal water-potential gradient (between the xylem and the epidermis) which drives water uptake for growth. For the four species it was small, between 0.3 and 0.6 bar, and so did not limit growth substantially.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00391104
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  • 13
    Electronic Resource
    Electronic Resource
    Characterization of long-term extension of isolated cell walls from growing cucumber hypocotyls (1989)
    Springer
    Planta 177 (1989), S. 121-130 
    Details
    ISSN: 1432-2048
    Keywords: Cell wall (viscoelastic properties) ; Cell wall enzymes ; Cell wall extension ; Creep of cell walls ; Cucumis ; Hypocotyl (growth)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Walls from frozen-thawed cucumber (Cucumis sativus L.) hypocotyls extend for many hours when placed in tension under acidic conditions. This study examined whether such “creep” is a purely physical process dependent on wall viscoelasticity alone or whether enzymatic activities are needed to maintain wall extension. Chemical denaturants inhibited wall creep, some acting reversibly and others irreversibly. Brief (15 s) boiling in water irreversibly inhibited creep, as did pre-incubation with proteases. Creep exhibited a high Q10 (3.8) between 20° and 30°C, with slow inactivation at higher temperatures, whereas the viscous flow of pectin solutions exhibited a much lower Q10 (1.35). On the basis of its temperature sensitivity, involvement of pectic gel-sol transitions was judged to be of little importance in creep. Pre-incubation of walls in neutral pH irreversibly inactivated their ability to creep, with a half-time of about 40 min. At 1 mM, Cu2+, Hg2+ and Al3+ were strongly inhibitory whereas most other cations, including Ca2+, had little effect. Sulfhydryl-reducing agents strongly stimulated creep, apparently by stabilizing wall enzyme(s). The physical effects of these treatments on polymer interactions were examined by Instron and stress-relaxation analyses. Some treatments, such as pH and Cu2+, had significant effects on wall viscoelasticity, but others had little or no apparent effect, thus implicating an enzymatic creep mechanism. The results indicate that creep depends on relatively rugged enzymes that are firmly attached to or entangled in the wall. The sensitivity of creep to SH-reducing agents indicates that thiol reduction of wall enzymes might provide a control mechanism for endogenous cell growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392162
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  • 14
    Electronic Resource
    Electronic Resource
    Mechanism of blue-light-induced plasma-membrane depolarization in etiolated cucumber hypocotyls (1992)
    Springer
    Planta 188 (1992), S. 199-205 
    Details
    ISSN: 1432-2048
    Keywords: Blue light and membrane depolarization ; Cucumis ; Light signal transduction ; Membrane voltage and resistance ; H+-ATPase (pump) inhibition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A large, transient depolarization of the plasma membrane precedes the rapid blue-light (BL)-induced growth suppression in etiolated seedlings of Cucumis sativus L. The mechanism of this voltage transient was investigated by applying inhibitors of ion channels and the plasma-membrane H+-ATPase, by manipulating extracellular ion concentrations, and by measuring cell input resistance and ATP levels. The depolarizing phase was not affected by Ca2+-channel blockers (verapamil, La3+) or by reducing extracellular free Ca2+ by treatment with ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA). However, these treatments did reduce the rate of repolarization, indicating an inward movement of Ca2+ is involved. No effects of the K+-channel blocker tetraethylammonium (TEA+) were detected. Vanadate and KCN, used to inhibit the H+-ATPase, reduced or completely inhibited the BL-induced depolarization. Levels of ATP increased by 11–26% after 1–2 min of BL. Input resistance of trichome cells, measured with double-barreled microelectrodes, remained constant during the onset of the depolarization but decreased as the membrane voltage became more positive than -90 mV. The results indicate that the depolarization mechanism initially involves inactivation of the H+-ATPase with subsequent transient activation of one or more types of ion channels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00216814
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  • 15
    Electronic Resource
    Electronic Resource
    Large plasma-membrane depolarization precedes rapid blue-light-induced growth inhibition in cucumber (1989)
    Springer
    Planta 178 (1989), S. 407-410 
    Details
    ISSN: 1432-2048
    Keywords: Blue light ; Cuoumis (elongation growth) ; Growth inhibition ; Hypocotyl (growth inhibition) ; Membrane depolarization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Blue-light (BL)-induced suppression of elongation of etiolated Cucumis sativus L. hypocotyls began after a 30-s lag time, which was halved by increasing the fluence rate from 10 to 100 μmol·m-2·s-1. Prior to the growth suppression, the plasma-membrane of the irradiated cells depolarized by as much as 100 mV, then returned within 2–3 min to near its initial value. The potential difference measured with surface electrodes changed with an identical time course but opposite polarity. The lag time for the change in surface potential showed an inverse dependence on fluence rate, similar to the lag for the growth inhibition. Green light and red light caused neither the electrical response nor the rapid inhibition of growth. The depolarization by BL did not propagate to nonirradiated regions and exhibited a refractory period of about 10 min following a BL pulse. Fluenceresponse relationships for the electrical and growth responses provide correlational evidence that the plasma-membrane depolarization reflects an event in the transduction chain of this light-growth response.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00391869
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  • 16
    Electronic Resource
    Electronic Resource
    Rapid alterations in growth rate and electrical potentials upon stem excision in pea seedlings (1992)
    Springer
    Planta 187 (1992), S. 523-531 
    Details
    ISSN: 1432-2048
    Keywords: Depolarization (growth-induced) ; Growth rate after excision ; Membrane potential ; Pisum (growth and electric potential) ; Slow wave potential ; Surface potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Excision of the epicotyl base of pea (Pisum sativum L.) seedlings in air results in a fast drop in the growth rate and rapid transient membrane depolarization of the surface cells near the cut. Subsequent immersion of the cut end into solution leads to a rapid, transient rise in the epicotyl growth rate and an acropetally propagating depolarization with an amplitude of about 35 mV and a speed of approx. 1 mm · s−1. The same result can be achieved directly by excision of the pea epicotyl under water. Shape, amplitude and velocity of the depolarization characterize it as a “slow-wave potential”. These results indicate that the propagating depolarization is caused by a surge in water uptake. Neither a second surge in water uptake (measured as a rapid increase in growth rate when the cut end was placed in air and then back into solution) nor another cut can produce the depolarization a second time. Cyanide suppresses the electrical signal at the treated position without inhibiting its transmission through this area and its development in untreated parts of the epicotyl. The large depolarization and repolarization which occur in the epidermal and subepidermal cells are not associated with changes in cell input resistance. Both results indicate that it is a transient shut-down of the plasma-membrane proton pump rather than large ion fluxes which is causing the depolarization. We conclude that the slow wave potential is spread in the stem via a hydraulic surge occurring upon relief of the negative xylem pressure after the hydraulic resistance of the root has been removed by excision.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00199972
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  • 17
    Electronic Resource
    Electronic Resource
    Stretch-activated chloride, potassium, and calcium channels coexisting in plasma membranes of guard cells of Vicia faba L. (1991)
    Springer
    Planta 186 (1991), S. 143-153 
    Details
    ISSN: 1432-2048
    Keywords: Guard cell ; Ion channel (Stretch activated) ; Mechanotransduction ; Patch clamp ; Voltage-dependence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Mechanosensitive ion channels in the plasma membrane of Vicia faba guard cell protoplasts were studied by use of the patch clamp technique. Stretch-activated (SA) channels in outside-out patches were analyzed for channel conductance, kinetics and ion selectivity. We found three distinct SA channels, permeable to Cl−, K+ and Ca2+ and distinguishable from spontaneous (non-SA) channels for these ions on the basis of conductance, kinetics, and voltage-dependence, as well as sensitivity to membrane stretch. In the attached patch configuration, light suction (2 to 10 kPa) reversibly induced channel opening with multiple amplitudes and complex kinetics. The open probability for SA channels increased nonlinearly with pipette suction. In guard cells in situ, these SA channels may mediate ion transport across the plasma membrane directly, as well as influence the activity of non-SA channels via effects on membrane voltage and cytoplasmic calcium. Through such effects, SA channels likely influence volume and turgor regulation of guard cells, and thereby control of leaf gas exchange.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00201510
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  • 18
    Electronic Resource
    Electronic Resource
    An oat coleoptile wall protein that induces wall extension in vitro and that is antigenically related to a similar protein from cucumber hypocotyls (1993)
    Springer
    Planta 191 (1993), S. 349-356 
    Details
    ISSN: 1432-2048
    Keywords: Acid growth ; Avena (coleoptile growth) ; Cell wall extension ; Expansin ; Protein (cell wall)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Plant cell walls expand considerably during cell enlargement, but the biochemical reactions leading to wall expansion are unknown. McQueen-Mason et al. (1992, Plant Cell 4, 1425) recently identified two proteins from cucumber (Cucumis sativus L.) that induced extension in walls isolated from dicotyledons, but were relatively ineffective on grass coleoptile walls. Here we report the identification and partial characterization of an oat (Avena sativa L.) coleoptile wall protein with similar properties. The oat protein has an apparent molecular mass of 29 kDa as revealed by sodium dodecyl sulfate-polyacrylamide gel eletrophoresis. Activity was optimal between pH 4.5 and 5.0, which makes it a suitable candidate for “acid growth” responses of plant cell walls. The oat protein induced extension in walls from oat coleoptiles, cucumber hypocotyls and pea (Pisum sativum L.) epicotyls and was specifically recognized by an antibody raised against the 29-kDa wall-extension-inducing protein from cucumber hypocotyls. Contrary to the situation in cucumber walls, the acid-extension response in heat-inactivated oat walls was only partially restored by oat or cucumber wall-extension proteins. Our results show that an antigenically conserved protein in the walls of cucumber and oat seedlings is able to mediate a form of acid-induced wall extension. This implies that dicotyledons and grasses share a common biochemical mechanism for at least part of acid-induced wall extensions, despite the significant differences in wall composition between these two classes of plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00195692
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  • 19
    Electronic Resource
    Electronic Resource
    Analysis of Peg Formation in Cucumber Seedlings Grown on Clinostats and in a Microgravity (Space) Environment (1999)
    Springer
    Journal of plant research 112 (1999), S. 507-516 
    Details
    ISSN: 1618-0860
    Keywords: Keywords: Cucumber, Development, Hook, Microgravity, Peg, Space
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Cucumis sativus L. cv Burpee Hybrid II) grown under conditions of normal gravity, microgravity, and simulated microgravity (clinostat rotation). Seeds were germinated on the ground, in clinostats and on board the space shuttle (STS-95) for 1–2 days, frozen and subsequently examined for their stage of development, degree of hook formation, number of pegs formed, and peg morphology. The frequency of peg formation in space-grown seedlings was found to be nearly identical to that of clinostat-grown seedlings and to differ from that of seedlings germinated under normal gravity only in a minority of cases; ˜6% of the seedlings formed two pegs and nearly 2% of the seedlings lacked pegs, whereas such abnormalities did not occur in ground controls. The degree of hook formation was found to be less pronounced for space-grown seedlings, compared to clinostat-grown seedlings, indicating a greater degree of decoupling between peg formation and hook formation in space. Nonetheless, in all seedlings having single pegs and a hook, the peg was found to be positioned correctly on the inside of the hook, showing that there is coordinate development even in microgravity environments. Peg morphologies were altered in space-grown samples, with the pegs having a blunt appearance and many pegs showing alterations in expansion, with the peg extending out over the edges of the seed coat and downwards. These phenotypes were not observed in clinostat or ground-grown seedlings.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00013907
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  • 20
    Electronic Resource
    Electronic Resource
    Plant cell enlargement and the action of expansins (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 533-540 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Plant cells are caged within a distended polymeric network (the cell wall), which enlarges by a process of stress relaxation and slippage (creep) of the polysaccharides that make up the load-bearing network of the wall. Protein mediators of wall creep have recently been isolated and characterized. These proteins, called expansins, appear to disrupt the noncovalent adhesion of matrix polysaccharides to cellulose microfibrils, thereby permitting turgor-driven wall enlargement. Expansin activity is specifically expressed in the growing tissues of dicotyledons and monocotyledons. Sequence analysis of cDNAs indicates that expansins are novel proteins, without previously known functional motifs. Comparison of expansin cDNAs from cucumber, pea, Arabidopsis and rice shows that the proteins are highly conserved in size and amino acid sequence. Phylogenetic analysis of expansin sequences suggests that this multigene family diverged before the evolution of angiosperms. Speculation is presented about the role of this gene family in plant development and evolution.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bies.950180704
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