A study, using copper-64, of various aspects of the retention of copper supplied via the plant leaf

Copper deposited in solution or in suspension on the surface of leaves is rapidly taken up by the plant; however, this uptake process ceases almost completely a few hours after application if the aqueous phase disappears. The amount of copper taken up by the plant increases with the copper concentration of the liquid applied. The uptake does not vary significantly as between nitrate and acetate, but is distinctly less with sulphate. It is only slightly affected by the choice of surfactant, although tween 80 has proved least efficient. The most satisfactory concentrations are 0.5 vol.% for vatsol and 0.1 vol.% for tween 20. The method of application of a given volume of liquid, in the form of one or several droplets, significantly affected the uptake in one experiment out of three. The greater part of the copper taken up by the plant (generally 85 to over 99%) is located in the part treated. By examining the deposition site with a scanning electron microscope, extracting the epicuticular wax, and studying the localization of the copper by secondary ion emission in the lamina treated, it was possible to show (with the help of acetate and oxide) that a large fraction of the copper fixed by the plant remains localized on the surface at least during the first 24 hours after deposition. (author)