Synergism Between Calcium Ions and Abscisic Acid in Preventing Stomatal Opening

Abstract

The inhibition of stomatal opening in Commelina communis L. by abscisic acid (ABA) appears to be dependent on the availability of calcium ions. Incubation of epidermal strips in 10"° mol m~^ ABA had little effect in the absence of calcium, and a factorial experiment showed a highly significant calcium x .^BA interaction. The effect of calcium appeared to be on the later stages of the opening process, and might have been the result of an inhibition of potassium uptake by the guard cells. There was no detectable effect of ABA when EGTA was used to chelate calcium from the apoplastic space.The data are consistent with the hypothesis that .\BA increases the permeability of the plasma membranes of the guard cells to calcium. Calcium might then operate as a second messenger to regulate the ionic fluxes that determine guard cell turgor.

The plant multidrug resistance ABC transporter AtMRP5 is involved in guard cell hormonal signalling and water use

“…(i) Increasing concentrations of external Ca 2 known to trigger stomatal closure under white light (Allen et al, 2001;DeSilva et al, 1985;Gilroy et al, 1990) classically induced stomatal closure in Ws-2 plants ( Figure 1b, closed circles), but had only a negligible effect on stomata of mrp5-1 plants ( Figure 1b, open squares).…”

Estimations of apoplastic concentrations of K+ and Ca2+ in the vicinity of stomatal guard cells

“…These factors may explain why after only 1 h of incubation no relationship was observed between the Ca^* concentration in the medium and stomatal aperture. Nevertheless, the presence of calcium in the apoplast appears to be essential for the promotion of closure either by darkness or by ABA (Schwartz, 1985;Atkinson et al, 1989) and concentrations above O'l mol m~^ can themselves cause stomatal closure in the light (De Silva et al, 1985), Although the relationship between apoplastic and cj'tosolic Ca^* is probably less straightforward than for K*, there is no doubt that increasing apoplastic Ca^* causes closure of open stomata. Schwartz (1985) found that having pre-incubated detached leaves of C. communis in tap water for 2 h, subsequent incubation of abaxial epidermal strips in 1 mol m~^ CaCl, reduced aperture to < 90%.…”

“…Previous data have reported increased stomatal opening in C. communis in response to increasing K* concentration (Travis & Mansfield, 1979) and a reduction in opening in response to increasing Ca^+ concentration (De Silva, Hetherington & Mansfield, 1985;Mansfield, Hetherington & Atkinson, 1990). Here we have found that, starting with open stomata, partial closure occurred in KCl concentrations of up to 50 mol m"^.…”

Mechanisms of action of abscisic acid at the cellular level

“…DeSilva et al, 1985) had suggested that there was a calcium requirement during ABA induced stomatal closure and that an increase in cytosolic free calcium ions might act to trigger the intraceliular machinery responsible for the reduction in guard cell turgor (see Mansfield et al, 1990). Recently, Gehring et al (1990) have demonstrated that application of ABA increased the concentration of free calcium ions in the cytosol of a number of tissues.…”