Calcium elevation-dependent and attenuated resting calcium-dependent abscisic acid induction of stomatal closure and abscisic acid-induced enhancement of calcium sensitivities of S-type anion and inward-rectifying K channels in Arabidopsis guard cells

Plant J. 2009 Jul;59(2):207-20. doi: 10.1111/j.1365-313X.2009.03872.x. Epub 2009 Mar 19.

Abstract

Stomatal closure in response to abscisic acid depends on mechanisms that are mediated by intracellular [Ca2+] ([Ca2+]i), and also on mechanisms that are independent of [Ca2+]i in guard cells. In this study, we addressed three important questions with respect to these two predicted pathways in Arabidopsis thaliana. (i) How large is the relative abscisic acid (ABA)-induced stomatal closure response in the [Ca2+]i-elevation-independent pathway? (ii) How do ABA-insensitive mutants affect the [Ca2+]i-elevation-independent pathway? (iii) Does ABA enhance (prime) the Ca2+ sensitivity of anion and inward-rectifying K+ channel regulation? We monitored stomatal responses to ABA while experimentally inhibiting [Ca2+]i elevations and clamping [Ca2+]i to resting levels. The absence of [Ca2+]i elevations was confirmed by ratiometric [Ca2+]i imaging experiments. ABA-induced stomatal closure in the absence of [Ca2+]i elevations above the physiological resting [Ca2+]i showed only approximately 30% of the normal stomatal closure response, and was greatly slowed compared to the response in the presence of [Ca2+]i elevations. The ABA-insensitive mutants ost1-2, abi2-1 and gca2 showed partial stomatal closure responses that correlate with [Ca2+]i-dependent ABA signaling. Interestingly, patch-clamp experiments showed that exposure of guard cells to ABA greatly enhances the ability of cytosolic Ca2+ to activate S-type anion channels and down-regulate inward-rectifying K+ channels, providing strong evidence for a Ca2+ sensitivity priming hypothesis. The present study demonstrates and quantifies an attenuated and slowed ABA response when [Ca2+]i elevations are directly inhibited in guard cells. A minimal model is discussed, in which ABA enhances (primes) the [Ca2+]i sensitivity of stomatal closure mechanisms.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Abscisic Acid / pharmacology*
  • Arabidopsis / genetics
  • Arabidopsis / metabolism
  • Arabidopsis / physiology*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism
  • Calcium / metabolism*
  • Ion Channel Gating
  • Mutation
  • Patch-Clamp Techniques
  • Plant Stomata / metabolism
  • Plant Stomata / physiology*
  • Potassium Channels, Inwardly Rectifying / genetics
  • Potassium Channels, Inwardly Rectifying / metabolism*

Substances

  • Arabidopsis Proteins
  • Potassium Channels, Inwardly Rectifying
  • Abscisic Acid
  • Calcium