PLANT PHYSIOLOGY , Vol 112, Issue 1 379-384, Copyright © 1996 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
NaCI Reduces Indole-3-Acetic Acid Levels in the Roots of Tomato Plants Independent of Stress-Induced Abscisic Acid
J. R. Dunlap and M. L. Binzel
Texas A&M Research and Extension Center, 2415 East Highway 83, Weslaco, Texas 78596 (J.R.D.)
Indole-3-acetic acid (IAA) was measured in leaves and roots of tomato
(Lycopersicon esculentum) genotypes subjected to salt stress. An abscisic
acid (ABA)-deficient mutant of tomato (sitiens), the genetic parent
(Rheinlands Ruhm, RR), and a commercial variety (Large Cherry Red, LCR) of
tomato were treated with 50 to 300 mM NaCl in nutrient culture. Both LCR
and RR had significantly higher levels of IAA in the roots compared with
that in sitiens prior to treatment. The initial levels of IAA in the roots
of LCR and RR declined by nearly 75% after exposure to NaCl, whereas those
in roots from the sitiens mutant remained unchanged. IAA levels in the
leaves of all genotypes remained unchanged or increased slightly in
response to NaCl. ABA was highest in leaves from the normal genotypes after
exposure to NaCl. ABA levels in the roots of sitiens were similar to the
levels in the normal genotypes, whereas levels in the leaves were only 10%
of the levels found in normal genotypes regardless of the salt treatment.
Treatment of LCR and sitiens with exogenous ABA increased the ABA levels in
leaves and roots, but there were no measurable changes in endogenous IAA.
Therefore, the reduction in IAA appears to result from an ABA-independent
effect of NaCl on IAA metabolism in the roots of stressed plants.
