The role of surface wax in susceptibility of plants to air pollutant injury

The relationship between quantity of epicuticular wax and plant sensitivity to hydrogen chloride (HCl) gas was investigated using 8-, 12-, and 16-day-old Phaseolus vulgaris L. plants exposed for 20 min to 27.6 ± 3.9 mg HCl.m^-3. Twelve-day-old plants were more sensitive than 8- or 16-day-old plants and possessed the lowest mean surface wax quantity. Multiple regression analysis showed that surface wax quantity was negatively linearly related to percent of leaves glazed. Necrotic injury was also negatively correlated with surface wax quantity, but to a lesser degree than glazing. Chamber temperature also affected the amount of necrotic injury incurred. Plant age and HCl concentration did not contribute to the observed variation in any of the injury variables in the regression analysis. The results of this study support the hypothesis that cuticular resistance, which is influenced by the amount of epicuticular wax, is a major factor influencing leaf glazing due to gaseous HCl. Since necrotic injury was affected by both surface wax quantity and chamber temperature, the incidence and severity of necrotic injury may be controlled by both cuticular and stomatal resistances.