(+) -Abscisic Acid: Identification, Measurement and Biosynthesis in Roots of Phaseolus vulgaris L.

Author

Mary L. Barr

Publication Date

5-2-1973

Abstract

Roots of Phaseolus vulgaris L. (var. Red Kidney) have been shown to play a significant role in contributing to the level of the plant hormone (+) -abscisic acid ((+) -ABA) in the growing plant. Furthermore, an environmental factor, water deficit has been shown to have a direct effect on the biosynthesis of (+) -ABA in roots. Presumed (+) -ABA from roots of red kidney bean was identified as (+) -ABA by its physical properties including optical rotatory dispersion (ORD), ultraviolet absorption, and chromatographic behavior and by its biological activity as observed in the lettuce seed germination bioassay and wheat coleoptile elongation bioassay. Extraction methods followed those of Milborrow (1967) and the extraction efficiency was measured by the racemate dilution method. The lettuce seed germination bioassay using Lactuca sativa L. (var. Grand Rapids) followed that of Reynolds (1970); and the wheat coleoptile bioassay performed with Triticum aestivum L. (var. Scout 66) followed Zeevaart (1971). Total (+) -ABA extracted from control roots ranged from 1.2 to 3.0 µg/100g fresh weight. From osmotically stressed roots or from roots of previously wilted plants the total amount of (+) -ABA extracted ranged from 8.8 to 24.8 µg/100g fresh weight. These values were determined by ORD measurements. The biosynthesis of (+) -ABA from 2-¹⁴C-mevalonic acid (MVA) was measured in excised intact roots and 20 mm root sections by determining the amount of radioactivity incorporated from the labeled precursor. The identity of the presumed compound as labeled (+) -ABA was established on the basis of the following criteria:

1) the band of radioactivity cochromatographed with synthetic (±) -ABA in three solvent systems,

2) the same labeled band from the chromatograms coincided with the zone of inhibitory activity in bioassays,

3) the same labeled band coincided with the band which gave an ORD spectrum identical to that of (±) -ABA,

4) the trimethylsilyl (TMS) derivatives of synthetic (±) -ABA and the labeled presumed (±) -ABA cochromatographed and the products showed inhibitory activity in the seed germination bioassay.

Once the ¹⁴C-(+) -ABA was identified, the hypothesis that in a state of water deficit the level of ¹⁴C-(+) -ABA is higher than in normally watered plant roots and that this is de novo synthesis could be tested. The levels of ¹⁴C-(+) -ABA were 12.3 and 16.5 times higher in roots from wilted plants than in controls. In root sections osmotically stressed with polyethylene glycol (mol wt 6,500 to 7,000) the levels of (+) -ABA, while higher than in control roots, were much lower than in roots from wilted plants. Factors contributing to this are discussed. Two unidentified inhibitory compounds which are labeled and recovered in the extraction for (+) -ABA are reported. The radioactivity associated with these fractions increased as a function of the length of time elapsed between exposure to the precursor and the time of the extraction.

Language

English

Document Type

Dissertation

Degree Name

Biology

Level of Degree

Doctoral

Department Name

UNM Biology Department

First Committee Member (Chair)

Gordon Verle Johnson

Second Committee Member

Loren David Potter

Third Committee Member

David Eugene Kidd

Fourth Committee Member

James Roman Gosz

Fifth Committee Member

Guido Herman Daub

Recommended Citation

Barr, Mary L.. "(+) -Abscisic Acid: Identification, Measurement and Biosynthesis in Roots of Phaseolus vulgaris L.." (1973). https://digitalrepository.unm.edu/biol_etds/607