Cadmium alteration of root physiology and potassium ion fluxes

Segments of oat (Avena sativa L.) roots which had been exposed to 1 millimolar CdSO₄ in quarter-strength Hoagland No. 1 solution exhibited decreased respiratory rates, ATP levels, membrane-bound ATPase activity, and reduced K⁺ fluxes. Respiration and ATP levels were decreased after a 2-hour treatment with 1 millimolar CdSO₄ to 65 and 75%, respectively, of control rates. A membrane-bound, Mg²⁺-dependent, K⁺-stimulated acid ATPase was rapidly inhibited to 12% of control activity in the presence of 1 millimolar CdSO₄. Potassium uptake into root segments was inhibited to 80% of control values after 30 minutes in the presence of CdSO₄. A 2-hour pretreatment of root segments with CdSO₄ inhibited K⁺ uptake to 15% of control values. Cytoplasmic K⁺ efflux was inhibited with 1 millimolar CdSO₄.

The rates and the degree of Cd²⁺ inhibition of the parameters listed above suggest that one of the first sites of Cd²⁺ action is the plasmalemma K⁺ carrier (ATPase) in oat roots.