ABA increases [Ca2+]cyto

influx through plasma membrane or release from internal compartments

Verapamil: an inhibitor of extracellular Ca2+ channels

TMB-8: an an inhibitor of intracellular Ca2+ channels

J. Exp. Bot. (1995) 46: 973-979

Microinjected Ca2+(cyto) sensitive dye- fura-2

Non-invasive method:

transgenetic plants expressing the gene for the calcium indicator protein

yellow cameleon

ABA-induced calcium oscillation in guard cells of Arabidopsis

Web Topic 23.9A Ca2+ binding fusion protein: Ca2+ indicator yellow cameleon

Composed 4 domains: enhanced cyan fluorescence protein (ECFP)

enhanced yellow fluorescence protein (EYFP)

calmodulin (CaM)

CaM-binding protein (M13)

The 535/480 emission ratio [Ca2+]cyto

* p. 606

Reactive oxygen species (ROS), inositol 1,4,5-triphosphate (IP3),

cyclic ADP-ribose (cADPR), self-amplifying

activate channel

* ABA nitric oxide cADPR stomatal closure

* p. 607R

Auxin-induced stomatal opening [Ca2+]cyto

the location and periodicity of calcium oscillations rather than the

overall concentration of cytosolic calcium, determine the cellular response.

Phalaenopsis: citric acid/ malate

¤ ABA inhibits the plasma membrane H+-ATPase

also contribute membrane depolarization indirectly

ABA inhibition proton pump is via increase [ca2+]cyto and alkalizatio

n of the cytosol (pH 7.677.94, p. 607R)

p. 452

¤ p. 603

ABA activate slow and rapid (06) anion channels in guard cells

large amounts of Cl- and malate2- to escape from the cell

depolarization (more positive) / calcium factor

open voltage-gated K+ efflux channels

( long-term membrane depolarization)

Anion channel inhibitors:

5-nitro-2,3-phenylpropylaminobenzoid (NPPB) – slow type

block ABA-induced stomatal closing

4,4’-diisothiocyanatostilbene-2,2’-disulfonic acid (DIDS) – rapid type

have no (02) effect on ABA-induced stomatal closing

¤ ABA prevents light-induced stomatal opening

– inhibit the inward K+ channel

¤ stomatal closing of guard cells under stress

prevent opening:

inhibit inward K+ channels and plasma membrane H+ pumps

promote closing:

activate outward anion channels, then active K+ efflux channels

ABA signaling involves both Ca2+ dep- and independent pathway

“network robustness”

Daily changes in stomatal aperture, and in sucrose and K+ content

Red light: only sucrose accumulation

Stomatal opening is associated primarily with K+ uptake, and

closing is associated with a decrease in sucrose content, why?

Plant cell (04) 16: 1143-1162 The ascorbic acid redox state controls guard cell signaling and stomatal movement