Calcium chloride penetrates plant cuticles via aqueous pores

Penetration of calcium chloride across astomatous cuticular membranes (CMs) isolated from leaves of Pyrus communis L. has been studied. Penetration wa s a first-order process when calcium chloride concentrations ranged from 2 g l(-1) to 10 g l(-1). Rate constants were increased 10-fold by adding wett ing agents but they did not depend on temperature. The accelerators tributy l phosphate and diethyl sebacate had no effect on rates of penetration. Inc reasing humidity over the salt residue on the CMs from 50 to 90% increased rate constants by about 2-fold. Extracting cuticular waxes from pear leaf C Ms increased rate constants by factors of 2 to 3, depending on humidity. Le af CMs from Malus domestica Borkh., Populus alba L., Stephanotis floribunda Brongn. and Schefflera actinophylla (Endl.) Harms were also permeable to C aCl2. Highest rate constants were observed with poplar CMs while Schefflera CMs exhibited the lowest permeability. By comparing these results with the well established transport properties of the lipophilic pathway it is conc luded that calcium chloride hexahydrate penetrated cuticular membranes via aqueous pores.