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Stomatal responses to exogenous abscisic acid (ABA), supplied to detached leaves via the transpiration stream, were examined in Lupinus angustifolius L., L. cosentinii Guss. and L. luteus L. Stomatal closure, indicated by reduced leaf conductance, was induced by ABA in all three species. This confirmed previous work with L. cosentinii, but contrasts with a report of stomatal insensitivity to ABA in L. luteus. Possible reasons for this are discussed. In all the lupin species, the abaxial leaf surface was more responsive to exogenous ABA than the adaxial surface. Comparable differences were also evident in stomatal closure in response to water deficits. ABA concentrations in abaxial and adaxial epidermal strips were found to be similar and to increase when plants were subjected to water deficits or fed ABA through the petiole. Differences in stomatal density on the two surfaces were consistent with differences in conductance observed between the surfaces of turgid leaves with low ABA levels, whilst the differential sensitivity of the two surfaces to ABA and water deficits may be related to differing amounts of ABA available per stomatal complex. The greater availability of ABA per stomatal complex on the abaxial compared to the adaxial epidermis when the lupins were subjected to water deficits or to exogenous ABA is consistent with the greater sensitivity to water deficits and ABA in abaxial compared to adaxial stomata.
The New Phytologist © 1991 New Phytologist Trust