PLANT PHYSIOLOGY , Vol 103, Issue 2 597-605, Copyright © 1993 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Characterization of Expression of Drought- and Abscisic Acid-Regulated Tomato Genes in the Drought-Resistant Species Lycopersicon pennellii
T. L. Kahn, S. E. Fender, E. A. Bray and M. A. O'Connell
Department of Botany and Plant Sciences, University of California, Riverside, California 92521-0124 (T.L.K., E.A.B.)
A number of genes are induced by drought stress, and some of these genes
are regulated by the plant hormone abscisic acid (ABA). In tomato
(Lycopersicon esculentum), four genes have been identified and isolated
that require elevated levels of endogenous ABA for expression: le4, le16,
le20, and le25. To gain a better understanding of the role of these genes
during stress, their expression has been studied in the drought-resistant
relative of tomato, Lycopersicon pennellii. It was determined that
homologous genes to all four of the L. esculentum genes were present in the
L. pennellii genome. Studies were undertaken to compare the expression
characteristics of these genes in L. esculentum, L. pennellii, and their
F1. Using two methods of water-deficit imposition, whole plants to which
water was withheld and detached leaves that were wilted to 88% of their
original fresh weight, it was demonstrated that transcripts of these genes
accumulated in L. pennellii in response to water deficit. In general, the
increase occurred after a longer period of water deficit in L. pennellii
than in tomato. As in drought-sensitive species, ABA levels were elevated
by drought stress in L. pennellii, although the levels were reduced
compared with those in tomato. All four tomato genes were responsive to ABA
in L. esculentum and the F1, but only three of the four genes (le16, le20,
and le25) were induced in response to exogenous application of ABA in L.
pennellii. The patterns of expression of these genes in L. pennellii are
generally similar to that of L esculentum; therefore, it is suggested that
these genes play a similar, yet undefined, role in both genotypes rather
than being genes that are responsible for the greater drought resistance of
L. pennellii.