A A Webb

Lancaster University, Lancaster, England, United Kingdom

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Publications (8)35.12 Total impact

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    ABSTRACT: The hypothesis that increases in cytosolic free calcium ([Ca2+]i) are a component of the CO2 signal transduction pathway in stomatal guard cells of Commelina communis has been investigated. This hypothesis was tested using fura-2 fluorescence ratio photometry to measure changes in guard cell [Ca2+]i in response to challenge with 700 µl l−1 CO2. Elevated CO2 induced increases in guard cell [Ca2+]i which were similar to those previously reported in response to abscisic acid. [Ca2+]i returned to resting values following removal of the CO2 and further application of CO2 resulted in a second increase in [Ca2+]i. This demonstrated that the CO2-induced increases in [Ca2+]i were stimulus dependent. Removal of extracellular calcium both prevented the CO2-induced increase in [Ca2+]i and inhibited the associated reduction in stomatal aperture. These data suggest that Ca2+ acts as a second messenger in the CO2 signal transduction pathway and that an increase in [Ca2+]i may be a requirement for the stomatal response to CO2.
    The Plant Journal 03/2002; 9(3):297 - 304. · 6.58 Impact Factor
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    ABSTRACT: There is much interest in the transduction pathways by which abscisic acid (ABA) regulates stomatal movements (ABA-turgor signalling) and by which this phytohormone regulates the pattern of gene expression in plant cells (ABA-nuclear signalling). A number of second messengers have been identified in both the ABA-turgor and ABA-nuclear signalling pathways. A major challenge is to understand the architecture of ABA-signalling pathways and to determine how the ABA signal is coupled to the appropriate response. We have investigated whether separate Ca2+-dependent and -independent ABA-signalling pathways are present in guard cells. Our data suggest that increases in [Ca2+]i are a common component of the guard cell ABA-turgor and ABA-nuclear signalling pathways. The effects of Ca2+ antagonists on ABA-induced stomatal closure and the ABA-responsive CDeT6-19 gene promoter suggest that Ca2+ is involved in both ABA-turgor signalling and ABA-nuclear signalling in guard cells. However, the sensitivity of these pathways to alterations in the external calcium concentration differ, suggesting that the ABA-nuclear and ABA-turgor signalling pathways are not completely convergent. Our data suggest that whilst Ca2+-independent signalling elements are present in the guard cell, they do not form a completely separate Ca2+-independent ABA-signalling pathway.
    The Plant Journal 06/2001; 26(3):351-62. · 6.58 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: Stomatal guard cells have proven to be an attractive system for dissecting the mechanisms of stimulus–response coupling i plants. In this review we focus on the intracellular signal transduction pathways by which extracellular signals bring abou closure and opening of the stomatal pore. It is proposed that guard cell signal transduction pathways may be organized int functional arrays or signalling cassettes that contain elements common to a number of converging signalling pathways. Th purpose of these signalling cassettes may be to funnel extracellular signals down onto the ion transporters that control th fluxes of ions that underlie stomatal movements. Evidence is emerging that specificity in guard cell signalling may be, i part, encoded in complex spatio–temporal patterns of increases in the concentration of cytosolic–free calcium ([Ca2+]cyt). It is suggested that oscillations in [Ca2+]cyt may generate calcium signatures that encode information concerning the stimulus type and strength. New evidence is presente that suggests that these calcium signatures may integrate information when many stimuli are present.
    Philosophical Transactions of The Royal Society B Biological Sciences 09/1998; 353(1374). · 6.23 Impact Factor
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    ABSTRACT: elements also operate in plant cells will be reviewed in this paper. This discussion will focus primarily on the Experimental investigations of stomatal guard cells role of such molecules in stomatal guard cell signal have provided valuable insights into the mechanisms transduction with particular emphasis on the Ca2+ mobil- which may underlie signalling in plants. To date a izing, NAD+ metabolite, cADPR and its possible role in variety of second messengers/signalling elements the generation of stimulus specificity. have been implicated in the control of guard cell physi- The stomatal guard cell has proved particularly attract- ology and in the perception of important physiological ive in the elucidation of pathways that mediate stimulus stimuli which affect this cell type. The present paper response coupling in plant cells because they are amenable examines such evidence, placing particular emphasis to cell physiological techniques and their physiological on the role of calcium-mobilizing second messengers. responses are rapid and can be easily quantified. These The possibility that several distinct signalling path- cells respond to a range of stimuli, causing changes in ways may operate in the guard cell is discussed, as cell turgor and thus stomatal pore size, due to fluxes of are the important implications that this may have for cations and anions across cell membranes (Assmann, signalling in this and other plant cell systems.
    Journal of Experimental Botany - J EXP BOT. 01/1998; 49(90001):339-349.
  • Source
    A A Webb, A M Hetherington
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    ABSTRACT: We show that guard cells from Arabidopsis thaliana plants carrying the abscisic acid-insensitive mutations abi1 and abi2 fail to respond to CO2 and extracellular calcium. This demonstrates that the signal transduction pathways for all three stimuli converge on, or close to, the ABI1 and ABI2 gene products.
    Plant physiology 09/1997; 114(4):1557-60. · 6.56 Impact Factor
  • 01/1996; Academic Press., ISBN: 0065-2296
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    ABSTRACT: CDeT6-19 is an ABA-regulated gene which has been isolated from Craterostigma plantagineum. The CDeT6-19 gene promoter has been fused to the beta-glucuronidase reporter gene (GUS) and used to stably transform Arabidopsis thaliana and Nicotiana tabacum. This construct has been shown to be expressed in stomatal guard cells and often in the adjacent epidermal cells of both species in response to both exogenous ABA and drought stress. These results indicate that the stomatal guard cell is competent to relay an ABA signal to the nucleus. In contrast GUS expression directed by the promoter from a predominantly seed-specific, ABA-regulated gene, Em, or the promoter from the ABA-regulated CDeT27-45 gene is not detectable in the epidermal or guard cells of tobacco or Arabidopsis in response to ABA. The fact that not all ABA-regulated gene promoters are active in stomatal guard cells suggests that effective transduction of the signal is dependent upon particular regions within the gene promoter or that guard cells lack all or part of the specific transduction apparatus required to couple the ABA signal to these promoters. This suggests that there are multiple ABA stimulus response coupling pathways. The identification of a regulatory sequence from an ABA-induced gene which is expressed in stomatal guard cells creates the possibility of examining the role of Ca2+ and other second messengers in ABA-induced gene expression.
    The Plant Journal 02/1995; 7(1):129-34. · 6.58 Impact Factor
  • Biochemical Society Transactions 12/1994; 22(4):949-52. · 2.59 Impact Factor