Phenylpropanoid and anthocyanin changes in low-temperature treated winter oilseed rape leaves

In mesophyll cells of winter oilseed rape leaves (Brassica napus L. var. oleifera L. cv. Jantar), grown for 3 weeks at 2 °C (CA tissues) and then exposed to a brief freezing (–5 °C for 18 h followed by 6 h at 2 °C in darkness, CAF samples), the contents of soluble phenolic acids and anthocyanins increased markedly as compared with non-acclimated (NA) tissues.In water-soluble phenolic fractions of the studied leaves four hydroxycinnamic acids (caffeic, p-coumaric, ferulic and sinapic acids) were identified by high performance liquid chromatography and gas chromatography-mass spectrometry techniques.In plants subjected to cold and then to freezing treatments, the levels of soluble p-coumaric, sinapic and ferulic acids increased about 3-, 4- and 5-fold, respectively. The level of caffeic acid practically did not change in CA leaves but it increased by about 70 % after the frost-thaw treatment. Acclimation of plants in cold and the frost-thaw treatment resulted in the promotionof phenolic esterification. High rates of accumulation of ferulic and sinapic acids in cold were associated with their almost complete esterification under these temperature conditions, whereas freezing treatment was required for increased esterification of p-coumaric and caffeic acids, the accumulation of which was lower in CA leaves. In leaves grown in cold for 3 weeks,a two-fold accumulation of anthocyanins was observed. The freezing treatment added nothing to the cold-dependent accumulation of anthocyanins. A possible role of soluble phenolic compounds in acclimation of leaves to low temperature is discussed.