The Effect Of Osmotic Stress On Calcium Channel And Ca²⁺-ATPase In Plasma Membrane Of Maize Root Tip Cell

As a secondary messenger in plant cell, cytosolic Ca²⁺ concentration directly reflects the changing of stimulation outside of the cell. Ca²⁺ play an important role in regulating plant response to osmotic stress and drought resistance. Ca²⁺-permeable inward channel and Ca²⁺-ATPase are important Ca²⁺ transports in plasma membrane. In this paper, the effect of osmotic stress on activity of calcium channel and Ca²⁺-ATPase was investigated to verify the role of cytosolic calcium in signal transduction of osmotic stimulation.By using whole-cell patch clamping, a hyperpolarization-activated calcium permeable channel was recorded in plasma membrane of maize root tip cell. After osmotic stimulation (PEG treatment), the current intensity increased remarkably, and the open voltage of the calium conductance elevated. ABA has sililar effect with osmotic stress. The activation of calcium channel initiated by ABA or osmotic stress can be strongly inhibited by EGTA, vepamil and TFP. The result suggest that osmotic stress may exert it effect by using ABA induced calcium influx through calcium channels which sensitive to verapamil, and intracellular calmodulin play a role in this signal cascade.Result from Ca²⁺-ATPase measurement show that osmotic stress or ABA can stimulate the activity of Ca²⁺-ATPase. This effect can be blocked by EGTA, verapamil or TFP; indicating that activation of Ca²⁺-ATPase may be also an important step in oamotic signal transduction.The result in this paper suggest that osmotic stress leads generation of ABA, ABA stimulate transmembrane calcium flux (influx through calcium channel and efflux through Ca²⁺-ATPase). Calcium dynamics play a key role in signal transduction of osmotic stress.