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Regulation of Gene Expression During Abiotic
Stresses and the Role of the Plant Hormone
Abscisic Acid
Elizabeth A. Bray
University of California, Riverside, California
735I. INTRODUCTION
The plant response to the environment is a complex set of processes. Changes in the environment result
in plant responses at many different levels: morphological, physiological, cellular, and metabolic. The
type of response depends on the source of the stress, the duration and severity of the stress, the genotype
of the stressed plant, the stage of development, and the organ and cell type in question. To fully under-
stand plant stress, the mechanism by which these responses are regulated and the function of the responses
must be characterized and understood. To further understand plant stress, researchers have turned to the
study of molecular responses. In this chapter, stresses discussed are water deficit, salt stress, and low-tem-
perature stress. A common link between these stresses is loss of cellular water.
As a result of the complex nature of the responses, it is difficult to determine the role of the various
responses with respect to resistance of the plant to the loss of water. Responses may be adaptive, con-
tributing to the ability of plant to withstand stress, may not be involved in adaptation, or may be a result
of injury. Among the many responses to changes in the environment are alterations in the pattern of gene
expression. Changes in gene expression are an important part of the plant response to the environment.
Although some responses, possibly short-term metabolic and physiological responses, may not require
changes in gene expression, the majority of responses to the environment are predicted to require alter-
ations in gene expression.
As there is a complex of responses to the environment, the mechanisms that control the plant re-
sponse to the environment are also expected to be complex. It is important to understand the cues from
the environment that are detected as stress and to understand the signaling mechanism(s) within the plant
at the whole plant and cellular levels. One plant signal that is prominent in plant stress studies is the plant
hormone abscisic acid (ABA). The concentration of ABA increases in the plant during stress [1]. The best
studied of the changes in ABA concentration is in response to drought stress. ABA levels increase in re-
sponse to lowered water potential, and it is postulated that the loss of turgor is the trigger that induces
ABA biosynthesis [2]. ABA levels have also been observed to rise in response to salt stress and low tem-
perature. The signal ABA is common to all of the stresses discussed in this chapter, although there are dif-
ferences in the pattern and magnitude of ABA accumulation in response to the different stresses. These
similarities have led to the suggestion that some of the responses to the various stresses are similar and
play similar roles in the ability of the plant to withstand periods of water deficit imposed by different en-
vironmental stresses.