Fatty acid and alkane changes in willow during frost-hardening

Abstract

Frost-hardening of 10 basket willow ( Salix viminalis) clones was studied by visual scoring of twig recuperation after controlled freezing treatments, together with measurements of total fatty acids, total n-alkanes (gas chromatography) and dry wts (% of fresh wt) of the twigs during the fall of 1994 in central Finland. The initial frost-tolerance of the clones was −5°. Hardening of the clones began at the end of September and proceeded similarly until mid October, when clonal differences became observable. The final frost-tolerances of the clones at the end of November varied from −37° to −80°, as 50% killing temperatures. Twig dry wts showed some increase prior to hardening, but an abrupt increase was observed during the first four weeks of hardening. After this, the increase in dry wts ceased. The total amount of twig n-alkanes (mg g −1 dry wt) decreased constantly prior to hardening until October. The total amounts of fatty acids (mg g −1 dry wt) decreased prior to hardening but doubled after hardening had begun. This increase in total fatty acids was accompanied by an abrupt increase in the ratio of unsaturated to saturated fatty acids. The amounts of linoleic (18:2) acid began to increase at the expense of linolenic (18:3) acid simultaneously with the beginning of hardening. No significant changes in fatty acids, n-alkanes or dry weights were observed during the late hardening stage. The differences in fatty acid profiles of the clones could not be attributed to clonal differences in frost-tolerances in the late hardening stage.