Organolead Toxicity in Plants: Triethyl Lead (Et3Pb+) Acts as a Powerful Transmembrane Cl-/OH- Exchanger Dissipating H+ -Gradients at Nano-Molar Levels

Abstract

Triethyl lead (Et3Pb+), a highly toxic oxidation product of the anti-knock agent tetraethyl lead (Et4Pb) was shown to act as anion (Cl-/OH-) antiporter in plant membranes, dissipating energy- dependent ion gradients, membrane potentials, and consequently turgor. This mechanism was demonstrated with tonoplast-type vesicles isolated from coleoptiles of Zea mays L. The ATP- driven H+ accumulation within those vesicles was abolished already at nano-molar levels of Et3Pb+, but only in the presence of Cl-. In intact cells the turgor dependent indole-3-acetic acid induced elongation growth of coleoptile segments of Avena sativa L. was inhibited by Et3Pb+ at micro-molar levels and after a lag of 15-20 min. This lag might be due to a slow penetration of the agent through the waxy cuticle and the cell wall.