Crystal occurrence and wax disruption on leaf surfaces of cabbage treated with simulated acid rain



Epicuticular waxes on leaves of Brassica oleracea L. (cabbage) were studied using scanning electron microscopy after a single treatment with simulated rain of pH 5.6, 3.0 or 2.5 which was either sprayed on to plants in an exposure chamber or applied as droplets with a micropipette. Treatments with acidified rain caused serious structural degradation of the wax crystals. The alteration of crystalline wax structures was similar for leaves treated with nitric acid solutions, but less severe, than for leaves treated with sulphuric acid solutions. With both H2SO4, and HNOa-derived rain solutions numerous gypsum (CaSO4) crystals were found in and near lesions on the leaves treated with rain of pH 3.0 and 2.5. The crystals probably resulted from damage of cuticular membranes by acidic rain which significantly altered their permeability to ions in the area of lesions. Crystalline leaf waxes may be an important target for acidic pollutants, and the physiological consequences of their degradation are discussed.