Protecting against water loss: analysis of the barrier properties of plantcuticles

The cuticle is the major barrier against uncontrolled water loss from leave s, fruits and other primary parts of higher plants. More than 100 mean valu es for water permeabilities determined with isolated leaf and fruit cuticle s from 61 plant species are compiled and discussed in relation to plant org an, natural habitat and morphology. The maximum barrier properties of plant cuticles exceed that of synthetic polymeric films of equal thickness. Cuti cular water permeability is not correlated to the thickness of the cuticle or to wax coverage. Relationships between cuticular permeability, wax compo sition and physical properties of the cuticle are evaluated. Cuticular perm eability to water increases on the average by a factor of 2 when leaf surfa ce temperature is raised from 15 degreesC to 35 degreesC. Organic compounds of anthropogenic and biogenic origin may enhance cuticular permeability. T he pathway taken by water across the cuticular transport barrier is reviewe d. The conclusion from this discussion is that the bulk of water diffuses a s single molecules across a lipophilic barrier while a minor fraction trave ls along polar pores. Open questions concerning the mechanistic understandi ng of the plant cuticular transport barrier and the role the plant cuticle plays in ensuring the survival and reproductive success of an individual pl ant are indicated.