GUARD CELL SIGNAL TRANSDUCTION Schroeder, Julian I; Allen, Gethyn J; Hugouvieux, Veronique ...
Annual review of plant physiology and plant molecular biology,
01/2001, Letnik:
52
Journal Article
Recenzirano
Guard cells surround stomatal pores in the epidermis of plant leaves and stems. Stomatal pore opening is essential for CO2 influx into leaves for photosynthetic carbon fixation. In exchange, plants ...lose over 95% of their water via transpiration to the atmosphere. Signal transduction mechanisms in guard cells integrate hormonal stimuli, light signals, water status, CO2, temperature, and other environmental conditions to modulate stomatal apertures for regulation of gas exchange and plant survival under diverse conditions. Stomatal guard cells have become a highly developed model system for characterizing early signal transduction mechanisms in plants and for elucidating how individual signaling mechanisms can interact within a network in a single cell. In this review we focus on recent advances in understanding signal transduction mechanisms in guard cells.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Drought is a major threat to agricultural production. Plants synthesize
the hormone abscisic acid (ABA) in response to drought, triggering a signalling
cascade in guard cells that results in stomatal ...closure, thus reducing water
loss. ABA triggers an increase in cytosolic calcium in guard
cells (Ca2+cyt) that
has been proposed to include Ca2+ influx across the plasma
membrane. However, direct recordings of Ca
2+ currents have been limited and the upstream activation
mechanisms of plasma membrane Ca2+ channels remain unknown.
Here we report activation of Ca2+-permeable channels in the
plasma membrane of Arabidopsis guard cells by hydrogen peroxide. The
H2O2-activated Ca2+ channels mediate
both influx of Ca2+ in protoplasts and increases in Ca
2+cyt in intact guard cells. ABA induces the production
of H2O2 in guard cells. If H2O2
production is blocked, ABA-induced closure of stomata is inhibited. Moreover,
activation of Ca2+ channels by H2O2 and
ABA- and H2O2-induced stomatal closing are disrupted
in the recessive ABA-insensitive mutant gca2. These data indicate that
ABA-induced H2O2 production and the H2O
2-activated Ca2+ channels are important mechanisms for
ABA-induced stomatal closing.
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Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Guard cells are located in the epidermis of plant leaves, and in pairs surround stomatal pores. These control both the influx of CO2 as a raw material for photosynthesis and water loss from plants ...through transpiration to the atmosphere. Guard cells have become a highly developed system for dissecting early signal transduction mechanisms in plants. In response to drought, plants synthesize the hormone abscisic acid, which triggers closing of stomata, thus reducing water loss. Recently, central regulators of guard cell abscisic acid signalling have been discovered. The molecular understanding of the guard cell signal transduction network opens possibilities for engineering stomatal responses to control CO2 intake and plant water loss.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A variety of stimuli, such as abscisic acid (ABA), reactive oxygen species (ROS), and elicitors of plant defense reactions, have been shown to induce stomatal closure. Our study addresses ...commonalities in the signaling pathways that these stimuli trigger. A recent report showed that both ABA and ROS stimulate an NADPH-dependent, hyperpolarization-activated Ca2+ influx current in Arabidopsis guard cells termed "ICa" (Z. M. Pei, Y. Murata, G. Benning, S. Thomine, B. Klüsener, G. J. Allen, E. Grill, J. I. Schroeder, Nature 2002 406: 731-734). We found that yeast (Saccharomyces cerevisiae) elicitor and chitosan, both elicitors of plant defense responses, also activate this current and activation requires cytosolic NAD(P)H. These elicitors also induced elevations in the concentration of free cytosolic calcium (Ca2+cyt) and stomatal closure in guard cells. ABA and ROS elicited Ca2+cyt oscillations in guard cells only when extracellular Ca2+ was present. In a 5 mM KCl extracellular buffer, 45% of guard cells exhibited spontaneous Ca2+cyt oscillations that differed in their kinetic properties from ABA-induced Ca2+ increases. These spontaneous Ca2+cyt oscillations also required the availability of extracellular Ca2+ and depended on the extracellular potassium concentration. Interestingly, when ABA was applied to spontaneously oscillating cells, ABA caused cessation of Ca2+cyt elevations in 62 of 101 cells, revealing a new mode of ABA signaling. These data show that fungal elicitors activate a shared branch with ABA in the stress signal transduction pathway in guard cells that activates plasma membrane ICa channels and support a requirement for extracellular Ca2+ for elicitor and ABA signaling, as well as for cellular Ca2+cyt oscillation maintenance.
Oscillations in cytosolic calcium concentration (Ca2+cyt) are central regulators of signal transduction cascades, although the roles of individual Ca2+cyt oscillation parameters in regulating ...downstream physiological responses remain largely unknown. In plants, guard cells integrate environmental and endogenous signals to regulate the aperture of stomatal pores and Ca2+cyt oscillations are a fundamental component of stomatal closure. Here we systematically vary Ca2+cyt oscillation parameters in Arabidopsis guard cells using a 'calcium clamp' and show that Ca2+cyt controls stomatal closure by two mechanisms. Short-term 'calcium-reactive' closure occurred rapidly when Ca2+cyt was elevated, whereas the degree of long-term steady-state closure was 'calcium programmed' by Ca2+cyt oscillations within a defined range of frequency, transient number, duration and amplitude. Furthermore, in guard cells of the gca2 mutant, Ca2+cyt oscillations induced by abscisic acid and extracellular calcium had increased frequencies and reduced transient duration, and steady-state stomatal closure was abolished. Experimentally imposing Ca2+cyt oscillations with parameters that elicited closure in the wild type restored long-term closure in gca2 stomata. These data show that a defined window of guard cell Ca2+cyt oscillation parameters programs changes in steady-state stomatal aperture.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abscisic acid (ABA) is a plant hormone involved in the response of plants to reduced water availability. Reduction of guard cell turgor by ABA diminishes the aperture of the stomatal pore and thereby ...contributes to the ability of the plant to conserve water during periods of drought. Previous work has demonstrated that cytosolic Ca2+ is involved in the signal transduction pathway that mediates the reduction in guard cell turgor elicited by ABA. Here we report that ABA uses a Ca2+-mobilization pathway that involves cyclic adenosine 5'-diphosphoribose (cADPR). Microinjection of cADPR into guard cells caused reductions in turgor that were preceded by increases in the concentration of free Ca2+ in the cytosol. Patch clamp measurements of isolated guard cell vacuoles revealed the presence of a cADPR-elicited Ca2+-selective current that was inhibited at cytosolic Ca2+ greater than or equal to 600 nM. Furthermore, microinjection of the cADPR antagonist 8-NH2-cADPR caused a reduction in the rate of turgor loss in response to ABA in 54% of cells tested, and nicotinamide, an antagonist of cADPR production, elicited a dose-dependent block of ABA-induced stomatal closure. Our data provide definitive evidence for a physiological role for cADPR and illustrate one mechanism of stimulus-specific Ca2+ mobilization in higher plants. Taken together with other recent data Wu. Y., Kuzma, J., Marechal, E., Graeff, R., Lee, H. C., Foster, R. & Chua, N.-H. (1997) Science 278, 2126-2130, these results establish cADPR as a key player in ABA signal transduction pathways in plants.
Cytosolic calcium oscillations control signaling in animal cells, whereas in plants their importance remains largely unknown. In wild-type Arabidopsis guard cells abscisic acid, oxidative stress, ...cold, and external calcium elicited cytosolic calcium oscillations of differing amplitudes and frequencies and induced stomatal closure. In guard cells of the V-ATPase mutant det3, external calcium and oxidative stress elicited prolonged calcium increases, which did not oscillate, and stomatal closure was abolished. Conversely, cold and abscisic acid elicited calcium oscillations in det3, and stomatal closure occurred normally. Moreover, in det3 guard cells, experimentally imposing external calcium-induced oscillations rescued stomatal closure. These data provide genetic evidence that stimulus-specific calcium oscillations are necessary for stomatal closure.
Cytosolic calcium increases were analyzed in guard cells of the Arabidopsis farnesyltransferase deletion mutant era1-2 (enhanced response to abscisic acid). At low abscisic acid (ABA) concentrations ...(0.1 μM), increases of guard cell cytosolic calcium and stomatal closure were activated to a greater extent in the era1-2 mutant compared with the wild type. Patch clamping of era1-2 guard cells showed enhanced ABA sensitivity of plasma membrane calcium channel currents. These data indicate that the ERA1 farnesyltransferase targets a negative regulator of ABA signaling that acts between the points of ABA perception and the activation of plasma membrane calcium influx channels. Experimental increases of cytosolic calcium showed that the activation of S-type anion currents downstream of cytosolic calcium and extracellular calcium-induced stomatal closure were unaffected in era1-2, further supporting the positioning of era1-2 upstream of cytosolic calcium in the guard cell ABA signaling cascade. Moreover, the suppression of ABA-induced calcium increases in guard cells by the dominant protein phosphatase 2C mutant abi2-1 was rescued partially in era1-2 abi2-1 double mutant guard cells, further reinforcing the notion that ERA1 functions upstream of cytosolic calcium and indicating the genetic interaction of these two mutations upstream of ABA-induced calcium increases.
Elevations in cytoplasmic calcium (Ca2+cyt) are an important component of early abscisic acid (ABA) signal transduction. To determine whether defined mutations in ABA signal transduction affect ...Ca2+cyt signaling, the Ca2+ -sensitive fluorescent dye fura 2 was loaded into the cytoplasm of Arabidopsis guard cells. Oscillations in Ca2+cyt could be induced when the external calcium concentration was increased, showing viable Ca2+ homeostasis in these dye-loaded cells. ABA-induced Ca2+cyt elevations in wild-type stomata were either transient or sustained, with a mean increase of approximately 300 nM. Interestingly, ABA-induced Ca2+cyt increases were significantly reduced but not abolished in guard cells of the ABA-insensitive protein phosphatase mutants abi1 and abi2. Plasma membrane slow anion currents were activated in wild-type, abi1, and abi2 guard cell protoplasts by increasing Ca2+cyt, demonstrating that the impairment in ABA activation of anion currents in the abi1 and abi2 mutants was bypassed by increasing Ca2+cyt. Furthermore, increases in external calcium alone (which elevate Ca2+cyt) resulted in stomatal closing to the same extent in the abi1 and abi2 mutants as in the wild type. Conversely, stomatal opening assays indicated different interactions of abi1 and abi2, with Ca2+ -dependent signal transduction pathways controlling stomatal closing versus stomatal opening. Together, Ca2+cyt recordings, anion current activation, and stomatal closing assays demonstrate that the abi1 and abi2 mutations impair early ABA signaling events in guard cells upstream or close to ABA-induced Ca2+cyt elevations. These results further demonstrate that the mutations can be bypassed during anion channel activation and stomatal closing by experimental elevation of Ca2+cyt.
Cytoplasmic free calcium (Ca2+cyt) acts as a stimulus-induced second messenger in plant cells and multiple signal transduction pathways regulate Ca2+cyt in stomatal guard cells. Measuring Ca2+cyt in ...guard cells has previously required loading of calcium-sensitive dyes using invasive and technically difficult micro-injection techniques. To circumvent these problems, we have constitutively expressed the pH-independent, green fluorescent protein-based calcium indicator yellow cameleon 2.1 in Arabidopsis thaliana (Miyawaki et al. 1999; Proc. Natl. Acad. Sci. USA 96, 2135-2140). This yellow cameleon calcium indicator was expressed in guard cells and accumulated predominantly in the cytoplasm. Fluorescence ratio imaging of yellow cameleon 2.1 allowed time-dependent measurements of Ca2+cyt in Arabidopsis guard cells. Application of extracellular calcium or the hormone abscisic acid (ABA) induced repetitive Ca2+cyt transients in guard cells. Ca2+cyt changes could be semi-quantitatively determined following correction of the calibration procedure for chloroplast autofluorescence. Extracellular calcium induced repetitive Ca2+cyt transients with peak values of up to approximately 1.5 microM, whereas ABA-induced Ca2+cyt transients had peak values up to approximately 0.6 microM. These values are similar to stimulus-induced Ca2+cyt changes previously reported in plant cells using ratiometric dyes or aequorin. In some guard cells perfused with low extracellular KCl concentrations, spontaneous calcium transients were observed. As yellow cameleon 2.1 was expressed in all guard cells, Ca2+cyt was measured independently in the two guard cells of single stomates for the first time. ABA-induced, calcium-induced or spontaneous Ca2+cyt increases were not necessarily synchronized in the two guard cells. Overall, these data demonstrate that that GFP-based cameleon calcium indicators are suitable to measure Ca2+cyt changes in guard cells and enable the pattern of Ca2+cyt dynamics to be measured with a high level of reproducibility in Arabidopsis cells. This technical advance in combination with cell biological and molecular genetic approaches will become an invaluable tool in the dissection of plant cell signal transduction pathways.
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