Cadmium Uptake by Pinus resinosa Ait. Pollen and the Effect on Cation Release and Membrane Permeability

Cadmium uptake by red pine (Pinus resinosa Ait.) pollen from a graded series of Cd(2+) solutions (0 to 2.88 microequivalents per 50 milligrams pollen) and its effect on membrane integrity were examined by atomic absorption spectroscopy. Uptake was strongly dependent on Cd(2+) concentration and was limited to adsorption and cation exchange in pollen walls during a 3-hour measurement period. Good correlation between measured Cd(2+) uptake and that predicted by the Langmuir and Freundlich isotherm equations indicated the adsorptive nature of Cd(2+) uptake. While substantial quantities of Ca(2+) and Mg(2+) were released by exchange mechanisms concurrent with Cd(2+) uptake, there was no evidence for leakage of cations due to membrane impairment as indicated by a poor correlation between Cd(2+) uptake and K(+) efflux. Virtually all Cd(2+) removed from solution was freely exchangeable with 0.5 millimolar CaCl(2) and demonstrated that Cd(2+) did not readily enter pine pollen but was adsorbed on the pollen wall. Ultraviolet transmission spectra of treatment solutions and analyses of phosphate and reducing sugar efflux also indicated that the potent toxicity of Cd(2+) to pollen germination and germ tube elongation was not the result of membrane damage.