Reactions of Corn Root Tissue to Calcium

Washing corn (Zea mays L.) root tissue in water causes loss of about one-third of the exchangeable Ca(2+) over the first 10 to 15 minutes. Upon transfer to K(+)-containing solutions, the tissue shows a short period of rapid K(+) influx which subsequently declines. Addition of 0.1 millimolar Ca(2+) decreases the initial rapid K(+) influx, but increases the sustained rate of K(+) and Cl(-) uptake. It was confirmed (Elzam and Hodges 1967 Plant Physiol 42: 1483-1488) that 0.1 millimolar Ca(2+) is more effective than higher concentrations for the initial inhibition, and that Mg(2+) will substitute.The inhibition arises from a mild shock affect of restoring Ca(2+). With 0.1 millimolar Ca(2+) net H(+) efflux is blocked for 10 to 15 minutes and the cells are depolarized by about 30 millivolts. However, 1 millimolar Ca(2+) rapidly produces increased K(+) influx and blocks net H(+) efflux for only a few minutes; blockage is preceded by a brief net H(+) influx which may restore and increase ion transport by reactivating the plasmalemma H(+)-ATPase.Stimulation of electrogenic H(+)-pumping with fusicoccin eliminates the shock responses and minimizes Ca(2+) effects on K(+) influx. Fusicoccin also strongly decreases Ca(2+) influx, but has no effect on Ca(2+) efflux. Ice temperatures and high pH decreased Ca(2+) efflux, but uncoupler and chlorpromazine did not.It is suggested that the inhibitory and promotive actions of Ca(2+) are manifested through decreases or increases in the protonmotive force.