Plant Physiol, February 2001, Vol. 125, pp. 935-942
The Effect of Exogenous Abscisic Acid on Stomatal Development,
Stomatal Mechanics, and Leaf Gas Exchange in Tradescantia
virginiana
Peter J.
Franks* and
Graham D.
Farquhar
School of Tropical Biology, James Cook University, P.O. Box 6811, Cairns, Queensland 4870, Australia (P.J.F.); and Environmental Biology
Group, Research School of Biological Sciences, Institute of Advanced
Studies, The Australian National University, G.P.O. Box 475, Canberra,
Australian Capitol Territory 2601, Australia (G.D.F.)
Gas exchange parameters and stomatal physical properties were
measured in Tradescantia virginiana plants grown under
well-watered conditions and treated daily with either distilled water
(control) or 3.0 mM abscisic acid (ABA). Photosynthetic
capacity (CO2 assimilation rate for any given leaf
intercellular CO2 concentration
[ci]) and relative stomatal sensitivity to
leaf-to-air vapor-pressure difference were unaffected by the ABA
treatment. However, at an ambient CO2 concentration
(ca) of 350 µmol mol
1,
ABA-treated plants operated with significantly lower
ci. ABA-treated plants had significantly
smaller stomata and higher stomatal density in their lower epidermis.
Stomatal aperture versus guard cell pressure
(Pg) characteristics measured with a cell
pressure probe showed that although the form of the relationship was
similar in control and ABA-treated plants, stomata of ABA-treated
plants exhibited more complete closure at
Pg = 0 MPa and less than half the
aperture of stomata in control plants at any given
Pg. Scaling from stomatal aperture versus
Pg to stomatal conductance versus Pg showed that plants grown under ABA
treatment would have had significantly lower maximum stomatal
conductance and would have operated with lower stomatal conductance for
any given guard cell turgor. This is consistent with the observation of
lower ci/ca in
ABA-treated plants with a ca of 350 µmol
mol1. It is proposed that the ABA-induced changes in
stomatal mechanics and stomatal conductance versus
Pg characteristics constitute an improvement
in water-use efficiency that may be invoked under prolonged drought conditions.
*
Corresponding author; e-mail peter.franks{at}jcu.edu.au; fax
61-7-4042-1284.
© 2001 American Society of Plant Physiologists
