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

Ethane was used as a tracer gas to assess the likelihood of thermo-osmotically induced mass-A ow in the aerenchyma of Avicennia marina seedlings 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 seedlings the flow increased with illumination, and in others it either decreased or remained unchanged. Overall, there was no statistically significant difference in the conductance to ethane between darkened and 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.