Ineffectiveness of Abscisic Acid in Stomatal Closure of Yellow Lupin,Lupinus luteusvar. Weiko III

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Abstract
Stomata of yellow lupin leaves are remarkably insensitive to abscisic acid (ABA). Stomatal resistance was monitored using both a viscous now porometer and a diffusion porometer. Results were confirmed with scanning electron microscopy. When exogenous ABA solutions were supplied via petioles, 10−6 M solutions had no effect on stomatal resistance. Upper (adaxial) stomata were not affected by 10−5 M ABA but lower stomata showed 3-fold more resistance after 2 h. Stomata of both surfaces closed after 30 min in 10−4 M ABA. Isolated epidermal peels of lupin leaves were floated on ABA solutions yet upper surface peels showed no stomatal closing in 10−4 M ABA, while lower surface stomata closed to a barely significant extent. Stomata of intact leaves were not very sensitive to darkness, showing at most a doubling in resistance after 6 h darkness. Complete stomatal closure, however, was readily produced by wilting leaves. Hence, lupin stomata are physically capable of closing. Endogenous ABA levels of water-stressed leaves increased approximately 10-fold, which corresponds to concentrations below 10 μM ABA. It is concluded that ABA is unlikely to play a role in controlling short-term stomatal response of lupins.

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