First and third author: Department of Plant Pathology, University of California, Davis 95616; and second author: Kearney Agriculture Center, 9240 S. Riverbend Avenue, Parlier, CA 93648
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Accepted for publication 30 October 1996.
An assay for determination of galacturonic acid with 3,5-dinitrosalicylic acid was developed that substantially extends the linear range of detection compared to a previously published method with this reagent. In the improved assay, galacturonic acid was detected with a reagent containing 44 mM 3,5-dinitrosalicylic acid, 4 mM sodium sulfite, and 375 mM sodium hydroxide. The absorbance of the solution after reaction with galacturonic acid was determined at 575 nm and was linear at concentrations of galacturonic acid up to 50 μmol, with a lower limit of detection at ~400 nmol. The assay with the improved reagent could be performed in wavelength ranges from 550 to 575 nm, with higher sensitivity at the shorter wavelengths. The new reagent was used in routine assays of polygalacturonase activity in culture filtrates of the important postharvest fungal pathogen Mucor piriformis.
© 1997 The American Phytopathological Society