Alterations in phenylpropanoid content in soybean roots during low temperature acclimation

L-Phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) activity, growth and phenolic acid content during low temperature acclimation in soybean (Glycine max. (L.) Merr.) roots were investigated. Elongation of soybean roots was inhibited after the transfer of 3-d-old seedlings grown at 25 to 10 °C. Extractable PAL activity as well as the total amount of phenolics increased 24 h after plant transfer to low temperature. The high pressure liquid chromatography analyses revealed the presence of six phenolic acids in soybean roots: p-hydroxybenzoic, vanillic, syringic, anisic, p-coumaric and ferulic. Analyses of different fractions of phenolic acids showed that during 24 h of low temperature exposure, an increase in the relative level of ester-bound-soluble phenolic acids occurred. The highest increase in this fraction was observed for ferulic acid (26 %). At the same time, a decrease in phenolic glycosides took place. The amount of phenolic acids released after alkaline treatment of the cell wall material was strongly inhibited (3-fold), which may suggest an alteration of the physical properties of the wall in acclimation to low temperature. The possible role of phenolics in acclimation to low temperature in roots is discussed.