Accumulation and transport of phenol, 2-nitrophenol, and 4-nitrophenol in plant cuticles

Partition (K) and permeance (P) coefficients have been determined for phenol, 2-nitrophenol, and 4-nitrophenol with isolated cuticles from mature tomato (Lycopersicon) and green pepper (Capsicum) fruits and from the adaxial surface of rubber (Ficus) leaves. Plant cuticular membranes (CM) are composed of a lipophilic, insoluble polymer matrix (MX) membrane and soluble cuticular lipids (SCL). Partition coefficients of the phenols (pH 3.0) for the system MX/buffer (MX/b) ranged from 43.6 to 164.9 and could be predicted from n-octanol/buffer (o/b) partition coefficients using the equation log KMX/b = 0.363 + 0.952 log Ko/b where (r = 0.986). In CM the K values were lower, especially for 4-nitrophenol, ranging from 32.4 to 110.8. The role of hydrogen bonding in partitioning of phenols into cuticles is discussed. Permeance coefficients for the cuticular membranes [P(CM)] ranged from 10(-10) (Ficus) to 10(-8) m sec-1 (Lycopersicon, Capsicum), with 2-nitrophenol permeating more rapidly than the other two phenols. Extraction of the SCL increased the permeance coefficients [P(MX)] by factors of approximately 5 (Lycopersicon), 50 (Capsicum), and 1000 (Ficus), respectively. The transport-limiting layer in plant cuticles acts as a diffusion and solubility barrier.