Uptake and localization of gaseous phenol and p-cresol in plant leaves

Understanding foliar uptake processes for organic air pollutants is critical to predicting the fate of these compounds, including their entry into the food chain and their susceptibility to plant-, microbe-, and light-mediated degradation. We characterized the uptake kinetics for gaseous phenol and p-cresol into the leaves of maize seedlings in a closed system over periods up to 23 h. When leaves were exposed to mixtures of phenol and p-cresol (3-50 μg l−1 each), the air concentrations of the compounds rapidly decreased, showing residence times of 4-6 h. The stomata of the leaves were mostly or completely closed, suggesting that uptake was primarily through the cuticle. The involvement of a cuticular uptake pathway was confirmed based on increased uptake into two cuticular mutants of maize. Models of the uptake data suggested that, at the concentrations used, phenol and p-cresol were taken up in a biphasic manner, consistent with previous two-compartment models for foliar uptake of lipophilic compounds via a cuticular pathway. These models also indicated that phenol was taken up at a slightly faster rate than p-cresol. To begin to understand the fate of these compounds, we examined the location of 14C in leaves exposed to 14C-phenol. Significantly more 14C accumulated in the terminal centimeter than in the central and basal regions of the leaves on both a mass and area basis. This is the first demonstration that a gaseous organic compound, or its breakdown products, accumulates in a spatially non-uniform manner in leaves following foliar uptake. These findings support a role for plants as natural, or deliberate, attenuators of airborne pollutants, and suggest potential availability of these compounds to the leaf surface microflora.