Foliar absorption of potassium and cuticular penetration characteristics of potassium and selected organic compounds

Abstract

The foliar absorption and cuticular penetration characteristics of selected potassium compounds, and the cuticular penetration characteristics of urea, phenol, 2-nitrophenol and 4-nitrophenol were studied. A wide range of absorption values was observed for foliar-applied potassium (1-48%) by excised Glycine max 'L. Bragg' leaves after 48 hr. In general, organic potassium salts had higher absorption values than the inorganic salts and few produced leaf burn. Mature Lycopersicon esculentum Mill. fruit were used as a model system to study absorption processes. Data from experiments in which selected K compounds were topically-applied to fruit disks were not correlated with the data from the experiments with excised Glycine leaves. Studies with isolated Lycopersicon fruit cuticles showed no significant differences in K permeability (using ('86)Rb as a tracer) for the selected K compounds under self-diffusion conditions. Partition (k), diffusion (D) and permeability (P) coefficients for urea, phenol, 2-nitrophenol and 4-nitrophenol with isolated cuticles from mature Capsicum annuum L. and Lycopersicon esculentum Mill 'Vendor' fruit and adaxial Citrus aurantium L. and Ficus elastica Roxb. 'Decora' leaves were measured at pH 3.0. Urea partition coefficients were low and not easily measured. Urea permeability coefficients for cuticular membranes ranged from 10('-11) (Capsicum and Ficus) to 10('-9) m s('-1) (Citrus and Lycopersicon). De-waxing the cuticular membrane (CM), to remove the soluble cuticular lipids (SCL) to yield the cutin polymer-matrix membrane (MX), led to a 1, 3, 13 and 22-fold increase in permeability for Lycopersicon, Citrus, Ficus and Capsicum, respectively. Partition coefficients in the system: cuticle/buffer(CM/b and MX/b) for the phenols were lower in the CM (32-111) than in the MX (44-165) membranes. Generally, phenol had the lowest and 4-nitrophenol had the highest k values. Partition coefficients for the MX membranes can be predicted from the k values for the phenols in the system n-octanol/buffer (o/b) with the equation: log k(MX/b) = 0.4233 + 0.9119 log k(o/b) (r = 0.996). Permeability coefficients for the CM membranes ranged from 10('-10) (Ficus) to 10('-8) m s('-1) (Capsicum and Lycopersicon). De-waxing led to 5, 50 and 1000-fold increases in permeability for Lycopersicon, Capsicum, and Ficus, respectively. For all CM and MX membranes, 2-nitrophenol generally had the highest P values.