Water Permeability

All terrestrial organisms have a problem in common; they must minimise water loss to the atmosphere and prevent desiccation. The driving force of transpiration at 25°C and 50% humidity is —95MPa, and at lower humidity it is even greater.Water supply is often short. Higher plants, insects and mammals use similar strategies to save water. They have generated membranes of very low water permeability at their interface with the dry air surrounding them most of the time. Synthetic polymers used for membranes, tubing, containers and other packaging materials also have low permeability to gases, water and other solvents to protect goods. Before we turn to permeability of cuticles and to strategies of plants to built effective barriers for protection against adverse influences from the environment,we will briefly compare water permeability of syntheticmembranes with permeance of plant polymermatrix membranes. Synthetic polymer membranes have been studied extensively during the last decades, and structure—permeability relationships have been established. What can we learn from homogeneous synthetic membranes to better understand permeability of heterogeneous plant cuticles?