Effect of Copper on Uptake of Diquat-14C by Hydrilla

A linear uptake of 14C-labeled 6,7-dihydrodipyrido (1,2-a:2′,1′-c)pyrazinediium ion (diquat-14C) at 1 ppmw by hydrilla (Hydrilla verticillata Casp.) occurred during a 10-day period under controlled conditions. Plant tissue contained higher amounts of radioactivity after treatment with combinations of 0.1 or 0.5 ppmw of diquat-14C plus 1 ppmw of copper than did tissue of plants in solutions of diquat-14C alone. Plants in a 1 ppmw of diquat-14C solution contained 2,123 cpm/mg after 8 days; however, 5,857 cpm/mg were measured in plant tissue taken after the same period from solutions containing diquat-14C plus 2 ppmw copper as copper sulfate pentahydrate (CSP). An increase in CSP from 3 to 10 ppmw did not significantly increase the uptake of diquat-14C over the 2 ppmw. Results with an organic copper complex (copper sulfate triethanolamine) in combination with diquat-14C were the same as those obtained with diquat-14C plus CSP.