Structure-activity relationships of ABA analogs based on their effects on the gas exchange of clonal white spruce (Picea glauca) emblings

1399-3054

Blackwell Publishing Journal Backfiles 1879-2005

Biology

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 (10−3M) 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.

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