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LANTHANUM UPTAKE IN ROOT PROTOPLASTS AND ITS EFFECTS ON ROOT GROWTH OF ZEA MAYS   L. M. Liu and K. H. Hasenstein, Biology Dept., UL Lafayette, LA 70504-2451

   Lanthanum (La³⁺) is a known Ca²⁺ antagonist but its mode of action is poorly understood. Growth studies with intact corn roots have shown that La³⁺ effects are concentration and time dependent. Concentrations less than 1 μM La³⁺ promote and higher than 500 μM inhibit growth. We used protoplasts and ICP-OES to study the time concentration and ion dependency of La³⁺ uptake. The uptake dynamics showed that initially La³⁺ binds to the membrane. After 30 min that component of uptake is saturated. Subsequent increases are likely to represent La³⁺ uptake into protoplasts. The measured rate of uptake was concentration dependent and amounted to 0.02, 0.918 nM and 4.976 nM per 1,000,000 protoplasts at 1, 100 and 1000 μM La³⁺, respectively. The calcium ionophore A23187 enhanced La³⁺ uptake for a <5 min but the long-term effects (30 min -5 hrs) depended on the ratio of La³⁺, Ca²⁺ and ionophore A23187. La³⁺ promoted the shifting of cortical microtubules (MT) in protoplasts from random to parallel within less than 5 hours. The data suggest that, in addition to acting as calcium ion channel blocker, La³⁺ might exerts more complex intracellular effects possibly related to protein expression and ion homeostasis.

(Supported by NASA: NAG10-190)