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Effect of Lanthanum on Ion Absorption in Corn Roots ¹

^a Departments of Plant Sciences and Biology, University of California, Riverside, California 92502

Short term (10 min) influx of ⁸⁶Rb-labeled potassium into corn (Zea mays L. WF9 x M14) root segments was inhibited by La (NO₃)₃ or LaCl₃. Half maximal inhibition of K⁺ influx from 0.25 mM KCl was obtained with 0.025 mM La³⁺. Kinetic analysis indicated the inhibition to be of a competitive nature. With absorption periods exceeding one hour, La³⁺ no longer inhibited, but rather stimulated K⁺ influx rates. La³⁺ was not an inhibitor of ³⁶Cl or ³²P absorption. Separated cortex and stele absorbed labeled potassium (and phosphate) at comparable rates, and La³⁺ inhibited potassium influx in both tissues. The effects of La³⁺ on ion absorption were similar to those of Ca²⁺, suggesting that the two polyvalent cations act at the same site. Based on this and the observation that La³⁺ does not seem to penetrate the plasma membrane, it was concluded that La³⁺ and Ca²⁺ affect changes in ion transport without entering cells.

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