Abscisic Acid

Abstract

Some molecules produced by plants exert their effects as negative regulators of various plant responses. Abscisic acid is an inhibitory hormone that helps plants adapt to stress. It also maintains water balance, prevents seed embryos from germinating, and induces seed and bud dormancy. Initial attempts to identify abscisic acid were made by Fredrick T. Addicott and his coworkers in cotton fruits in 1963. It was earlier suspected that seed and bud dormancy are caused by some inhibitory compounds and attempts were made to extract these compounds from various plant tissues. Acidic compounds separated by paper chromatography from these tissues were tested for their ability to promote growth in oat coleoptile, but instead these compounds inhibited coleoptile elongation. This compound was referred as “β-inhibitor complex.” Subsequently, high β-inhibitor levels were correlated with suppression of sprouting in Solanum tuberosum tubers, abortion of Lupinus arboreus pods, and bud dormancy in trees like Betula pubescens. This compound was subsequently named abscisin II, since it was identical to a substance that promotes abscission in cotton fruits (commercially important for mechanization of cotton picking). Eagles and Wareing (1963) also isolated a substance from Betula pubescens, a deciduous plant, which inhibits growth and induces bud dormancy. It was named “dormin.” “Dormin” was subsequently found to be structurally similar to “abscisin II.” The compound was subsequently renamed as abscisic acid (ABA)—a compound which inhibits growth and stomatal opening when plants are under environmental stress.

Multiple-Choice Questions

• 1. “Dormin” was isolated from which of the following plant species?

  • (a) Solanum tuberosum

  • (b) Lupinus arboreus

  • (c) Betula pubescens

  • (d) Lemna minor

• 2. The cyclohexane ring of ABA has an asymmetric carbon at which position?

  • (a) 1

  • (b) 2

  • (c) 3

  • (d) 4

• 3. Which of the following is not an ABA-mediated response in plants?

  • (a) Stomatal closure

  • (b) Desiccation tolerance

  • (c) Seed dormancy

  • (d) Promotion of seed germination

• 4. ABA is synthesized in which of the following cellular organelle?

  • (a) Mitochondria

  • (b) Endoplasmic reticulum

  • (c) Chloroplast

  • (d) Golgi bodies

• 5. Which of the following is a natural growth inhibitor which has physiological properties similar to ABA?

  • (a) Xanthoxin

  • (b) Violaxanthin

  • (c) Phaseic acid

  • (d) Isopentenyl diphosphate

• 6. During ABA-mediated stomatal closure, membrane depolarization is caused by net influx of which of the following ions?

  • (a) Chloride

  • (b) Potassium

  • (c) Hydrogen

  • (d) Calcium

Answers

1. c

2. a

3. d

4. c

5. a

6. c