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Biomedical subjects

M R McAinsh

Publications and source records attributed to M R McAinsh.

10 recordsLinked to original sources
PubMed2001

Drought-induced guard cell signal transduction involves sphingosine-1-phosphate.

Stomata form pores on leaf surfaces that regulate the uptake of CO2 for photosynthesis and the loss of water vapour during transpiration. An increase in the cytosolic concentration of free calcium ions ([Ca2+]cyt) is a common intermediate in many of the pathways leading to either opening or closure of the stomatal pore. This observation has prompted investigations into how specificity is controlled in calcium-based signalling systems in plants. One possible explanation is that each stimulus generates a unique increase in [Ca2+]cyt, or 'calcium signature', that dictates the outcome of the final response. It has been suggested that the key to generating a calcium signature, and hence to understanding how specificity is controlled, is the ability to access differentially the cellular machinery controlling calcium influx and release from internal stores. Here we report that sphingosine-1-phosphate is a new calcium-mobilizing molecule in plants. We show that after drought treatment sphingosine-1-phosphate levels increase, and we present evidence that this molecule is involved in the signal-transduction pathway linking the perception of abscisic acid to reductions in guard cell turgor.

Abscisic Acid↗
PubMed2001

Changes in stomatal behaviour in the calcicole Leontodon hispidus due to the disruption by ozone of the regulation of apoplastic Ca2+ by trichomes.

Regulation of the concentration of Ca2+ in the apoplast of plants is essential in order to allow Ca(2+)-dependent processes, such as Ca(2+)-mediated signal transduction in stomatal guard cells, to function correctly. This is particularly important for plants growing with high levels of Ca2+ in the rhizosphere. Recently, we have shown that in two calcicoles, Leontodon hispidus L. and Centaurea scabiosa L., trichomes play a key role in this regulatory process. Ozone is known to have a marked effect on plant Ca2+ homeostasis. Therefore, we have examined the effect of this pollutant on the regulation by trichomes of apoplastic Ca2+ in the calcicole L. hispidus. Treatment with 100 nl l-1 ozone resulted in a reduction in stomatal conductance of approximately 25% in plants grown with 15 mM Ca2+ in the rhizosphere. Analysis of total Ca2+ levels revealed that these changes in stomatal behaviour reflect a decrease in the ability of trichomes to sequester Ca2+. The amount of Ca2+ present in the trichome tip cell was reduced by approximately 38%. This was accompanied by an increase in the levels of Ca2+ in the guard cells and other tissues of the leaf. These data suggest that ozone has a detrimental effect on the ability of trichomes to regulate the concentration of apoplastic Ca2+ in L. hispidus, resulting in altered stomatal behaviour, and hence gaseous exchange, possibly due to the disruption of guard-cell Ca(2+)-mediated signal transduction. This has important implications for the growth and survival of plants growing in Ca(2+)-rich soils.

Adaptation, Physiological↗
PubMed2001

Calcium oscillations in higher plants.

There is considerable interest in the possibility that stimulus-induced oscillations in cytosolic free calcium encode information that is used to specify the outcome of the final response in calcium-based signalling pathways in plants. Recent results provide conclusive evidence that plant cells can decipher complex calcium signatures.

Calcium↗
PubMed2000

Ca2+signalling in stomatal guard cells.

Ca(2+) is a ubiquitous second messenger in the signal transduction pathway(s) by which stomatal guard cells respond to external stimuli. Increases in guard-cell cytosolic free Ca(2+) concentration ([Ca(2+)](cyt)) have been observed in response to stimuli that cause both stomatal opening and closure. In addition, several important components of Ca(2+)-based signalling pathways have been identified in guard cells, including the cADP-ribose and phospholipase C/Ins(1, 4,5)P(3)-mediated Ca(2+)-mobilizing pathways. The central role of stimulus-induced increases in [Ca(2+)](cyt) in guard-cell signal transduction has been clearly demonstrated in experiments examining the effects of modulating increases in [Ca(2+)](cyt) on alterations in guard-cell turgor or the activity of ion channels that act as effectors in the guard-cell turgor response. In addition, the paradox that Ca(2+) is involved in the transduction of signals that result in opposite end responses (stomatal opening and closure) might be accounted for by the generation of stimulus-specific Ca(2+) signatures, such that increases in [Ca(2+)](cyt) exhibit unique spatial and temporal characteristics.

Adenosine Diphosphate Ribose↗
PubMed1999

Abscisic acid induces oscillations in guard-cell cytosolic free calcium that involve phosphoinositide-specific phospholipase C.

Oscillations in cytosolic free Ca2+ concentration ([Ca2+]cyt) are an important component of Ca2+-based signal transduction pathways. This fact has led us to investigate whether oscillations in [Ca2+]cyt are involved in the response of stomatal guard cells to the plant hormone abscisic acid (ABA). We show that ABA induces oscillations in guard-cell [Ca2+]cyt. The pattern of the oscillations depended on the ABA concentration and correlated with the final stomatal aperture. We examined the mechanism by which ABA generates oscillations in guard-cell [Ca2+]cyt by using 1-(6-[17beta-3-methoxyestra-1,3, 5(10)-trien-17-yl]aminohexyl)-1H-pyrrole-2,5-dione (U-73122), an inhibitor of phosphoinositide-specific phospholipase C (PI-PLC)-dependent processes in animals. U-73122 inhibited the hydrolysis of phosphatidylinositol 4,5-bisphosphate by a recombinant PI-PLC, isolated from a guard-cell-enriched cDNA library, in a dose-dependent manner. This result confirms that U-73122 is an inhibitor of plant PI-PLC activity. U-73122 inhibited both ABA-induced oscillations in [Ca2+]cyt and stomatal closure. In contrast, U-73122 did not inhibit external Ca2+-induced oscillations in guard-cell [Ca2+]cyt and stomatal closure. Furthermore, there was no effect of the inactive analogue 1-(6-[17beta-3-methoxyestra-1,3, 5(10)-trien-17-yl]aminohexyl)-2,5-pyrrolidinedione on recombinant PI-PLC activity or ABA-induced and external Ca2+-induced oscillations in [Ca2+]cyt and stomatal closure. This lack of effect suggests that the effects of U-73122 in guard cells are the result of inhibition of PI-PLC and not a consequence of nonspecific effects. Taken together, our data suggest a role for PI-PLC in the generation of ABA-induced oscillations in [Ca2+]cyt and point toward the involvement of oscillations in [Ca2+]cyt in the maintenance of stomatal aperture by ABA.

Journal Article↗
PubMed1999

Dissection of the ozone-induced calcium signature.

The cellular responses of plants to numerous extracellular stimuli are mediated by transient elevations in the concentration of cytosolic free calcium ([Ca2+]cyt). We have addressed the question of how cells can use this apparently ubiquitous system to initiate so many specific and appropriate end responses. We show that the pollutant gas ozone elicits a biphasic Ca2+ response in intact Arabidopsis plants and a subsequent increase in expression of the gene encoding the antioxidant defence enzyme glutathione-S-transferase (GST). The second of the two [Ca2+]cyt peaks, but not the first, could be eliminated either by pre-treatment of plants with lanthanum chloride, or by reducing the duration of ozone fumigation. Under these conditions, ozone-induced GST expression was abolished. These data provide a functional dissection of the ozone Ca2+ signalling pathway and indicate that the second ozone-induced [Ca2+]cyt peak provides the necessary information to direct expression of GST.

Arabidopsis↗
PubMed1998

Abscisic acid-induced stomatal closure mediated by cyclic ADP-ribose.

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+ >/= 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.

Journal Article↗
PubMed1995

ABA-regulated promoter activity in stomatal guard cells.

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.

Abscisic Acid↗