Effect of Surfactant on Ion Penetration Through Leaf Wax and a Wax Model1

Leaves of nonglaucous cotton and tomato absorbed Mn whether or not a surfactant was added to a MnSO 4 spray solution, whereas the leaves of glaucous cabbage and onion absorbed Mn only when a surfactant was added. Manganese was absorbed by cabbage leaves only when a surfactant was added or when leaf surface wax formation was inhibited by ethyl N,N-dipropylthiolcarbamate (EPTC). Non-glaucous and glaucous pea mutants did not significantly absorb Mn unless surfactant was added to a MnSO 4 spray, after which both mutants equally absorbed Mn. Surfactants increased the concn of 59 fe penetrating into a wax paraffin model to a 0.5 mm depth by 8- to 30-fold over a no-surfactant treatment. Both the rate and depth of penetration were increased by surfactant. No Fe was absorbed by cabbage leaves unless surfactant was present in the spray solution or the leaf wax was disturbed by brushing. Thus, surfactant efficiently overcame an external leaf wax layer as a barrier to the absorption of foliar applied ions and thereby increased ion movement into the leaf.