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Structure‐activity relationships of ABA analogs based on their effects on the gas exchange of clonal white spruce ( Picea glauca ) emblings
Author(s) -
Fuchs Edgar E.,
Livingston N. J.,
Abrams S. R.,
Rose P. A.
Publication year - 1999
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1034/j.1399-3054.1999.105209.x
Subject(s) - chemistry , stereochemistry , double bond , triple bond , side chain , seedling , enantiomer , molecule , botany , organic chemistry , biology , polymer
ABA analog structure‐function relationships were determined by testing an array of 19 different ABA analogs on 1‐year‐old clonal white spruce ( Picea glauca [Moench.] Voss) raised from somatic embryos. The contribution of specific structural features to analog activity was determined from the relative effect of aeroponically applied analog solutions (10 −3 M ) on seedling gas exchange. Seedling transpiration rate (E) and carbon assimilation rate (A) were measured continuously during treatment by means of a whole plant cuvette system. The analogs were racemic about the C‐1′ chiral center and were derived from changes imposed on six regions of the ABA molecule. The activity of optically pure (+)‐S‐ABA and (−)‐R‐ABA were also determined. Analog activity was reduced by changing the oxidation level at C‐1 from the carboxylic acid. The ring C‐2′, C‐3′ double bond was important but not essential to activity. The activity lost through changes in ring structure and C‐1 oxidation level was, in many cases, almost fully restored by replacing the C‐4, C‐5 double bond with a triple bond. Therefore, analogs with a triple bond at C‐4 were more active than their equivalents with a dienoic side chain. Fluorination of the C‐7′ methyl caused a relatively moderate reduction in analog activity. Truncation of C‐1 and C‐2 from the side chain reduced activity to near zero. The unnatural (−)‐ABA enantiomer was inactive.