TAILIEUCHUNG - Plant physiology - Chapter 23 Abscisic Acid: A Seed Maturation and Antistress Signal

THE EXTENT AND TIMING OF PLANT GROWTH are controlled by the coordinated actions of positive and negative regulators. Some of the most obvious examples of regulated nongrowth are seed and bud dormancy, adaptive features that delay growth until environmental conditions are favorable. For many years, plant physiologists suspected that the phenomena of seed and bud dormancy were caused by inhibitory compounds, and they attempted to extract and isolate such compounds from a variety of plant tissues, especially dormant buds. Early experiments used paper chromatography for the separation of plant extracts, as well as bioassays based on oat coleoptile growth. These. | Chapter 23 Abscisic Acid A Seed Maturation and Antistress Signal THE EXTENT AND TIMING OF PLANT GROWTH are controlled by the coordinated actions of positive and negative regulators. Some of the most obvious examples of regulated nongrowth are seed and bud dormancy adaptive features that delay growth until environmental conditions are favorable. For many years plant physiologists suspected that the phenomena of seed and bud dormancy were caused by inhibitory compounds and they attempted to extract and isolate such compounds from a variety of plant tissues especially dormant buds. Early experiments used paper chromatography for the separation of plant extracts as well as bioassays based on oat coleoptile growth. These early experiments led to the identification of a group of growth-inhibiting compounds including a substance known as dormin purified from sycamore leaves collected in early autumn when the trees were entering dormancy. Upon discovery that dormin was chemically identical to a substance that promotes the abscission of cotton fruits abscisin II the compound was renamed abscisic acid ABA see Figure to reflect its supposed involvement in the abscission process. It is now known that ethylene is the hormone that triggers abscission and that ABA-induced abscission of cotton fruits is due to ABA s ability to stimulate ethylene production. As will be discussed in this chapter ABA is now recognized as an important plant hormone in its own right. It inhibits growth and stomatal opening particularly when the plant is under environmental stress. Another important function is its regulation of seed maturation and dormancy. In retrospect dormin would have been a more appropriate name for this hormone but the name abscisic acid is firmly entrenched in the literature. OCCURRENCE CHEMICAL STRUCTURE AND MEASUREMENT OF ABA Abscisic acid has been found to be a ubiquitous plant hormone in vascular plants. It has been detected in mosses but appears to be absent in 540 .

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