Fig 18 71 Some of the known interactions

Fig 18. 71 Some of the known interactions in the plant cell signal transduction network.

6. Calcium-permeable channels in the plasma membrane provide potential routes for entry of Ca 2+ to the cytosol during signal transduction. 1) Transient Ca 2+ increase is central to signal transduction. 2) Ca 2+ permeable channels : activation of increase in cytosolic Ca 2+, upstream elements in Ca 2+ - based signal transduction pathway, 3) Voltage-gated Ca 2+_ permeable channels are activated by membrane depolarization.

Calcium-based signal transduction in a typical plant cell.

Activation of a wheat root plasma membrane Ca 2+ channel by voltage.

Activation of plasma membrane Ca 2+ channel by stretch. may be responsible for the signaling during the early stages of mechano-sensory transduction. (touch, wind )

7. Calcium-permeable channels in endomembranes are activated by both voltage and ligands

(A) Diagram illustrating channel activities at the guard cell vacuolar membrane during stomatal closure (B) During plasma membrane-based signal transduction

Activity of the SV channel increases with increasing cytosolic concentration of Ca 2+ (A) Slow activation of the SV channel in barley aleurone vacuoles in response to positive voltages (B) Ca 2+-dependence of whole-vacuole channel activity. Increasing free calcium above approximately 1μM increasing the activity of the channel. Ca 2+ is thought to interact with calmodulin associated with the channel or a channel regulatory protein

8. Plasma membrane anion channels facilitate salt release during turgor adjustment and elicit membrane depolarization after stimulus perception

Anion channels in guard cell (A) Current-voltage relationship for rapidly activating (R-type) anion channels. (B) Current-voltage relationship for slowly activating (S-type) channels

Function of Anion channels 1. Controling salt release during turgor adjustment stimulus loss of Cl- depolarization open outward K+ channel loss of turgor pressure 2. To depolarize the plasma membrane leads the activation of voltage-gated Ca 2+ channels 3. Are activated by extreme membrane hyperpolarization

9. Vacuolar malate channels participate in malate sequestration

Current-voltage relationship for vacuolar uptake of malate through time-dependent anion channel in the tonoplast. Malate uptake by anion channel is strongly promoted by negative membrane otentials and increases with cytosolic malate concentration. In this figure, cytosolic malate concentration were 10 m. M(filled squares), 20 m. M(open squares), 50 m. M(open circles), and 100 m. M(filled triangles)- all with a vacuolar malate concentration of 10 m. M. Malate uptake with equal concentration of malate(50 m. M) presente on both side of the membrane is indicated by stars.

Accumulation of malate in the root of CAM plants. Malate 2 - is thought to enter the vacuole though malate-selective channels. These channel are strongly inward rectifying and do not allow substantial malate 2 - efflux. Once inside the vacuole, malate 2 - is protonated to H. malate and H 2. malate 0. This maintains the effective concentration difference for malate 2 - across the membrane.

10. Integrated channel activity at the vacuolar and plasma membranes yields sophisticated signaling systems

Ca 2+ signaling coordinates the activities of multiple ion channels and H+-pumps during stomatal closure. In this model, perception of ABA by a receptor(R) results in an increase in cytosolic free Ca 2+ through Ca 2+ influx or Ca 2+ release from internal stores. Increased cytosolic Ca 2+ promotes opening of plasma membrane anion and K+out channels and inhibits opening of K+in channels. As more ions leave the cell than enter it, water follows, turgor is lost, and the stomatal pore is closed