THERMO-OSMOTIC GAS-SUPPLY NOT DETECTED IN AVICENNIA-MARINA SEEDLINGS

Ethane was used as a tracer gas to assess the likelihood of thermo-osm otically induced mass-A ow in the aerenchyma of Avicennia marina seedl ings without pneumatophores. Ethane movement was measured in darkness and with illumination at approximately 600 mu mol m(-2) s(-1) provided to the leaves and stem, with the expectation that leaf warming under illumination would provide a means for thermo-osmotic flow. In some se edlings the flow increased with illumination, and in others it either decreased or remained unchanged. Overall, there was no statistically s ignificant difference in the conductance to ethane between darkened an d illuminated plants, and the rates of ethane movement were consistent with an average diffusive conductance to oxygen down the stem of 0.22 x 10(-9) m(3) s(-1). It was concluded that there was no evidence for thermo-osmotically induced flow in this case.