Submitted to: Plant Physiology Supplement
Publication Type: Abstract Only
Publication Acceptance Date: March 5, 1998
Publication Date: N/A
Technical Abstract: Significant increases in freezing tolerance have been observed in wheat, barley, rye and oat after exposure of plants to below freezing temperatures but before freezing injury occurs (-3C for 3 or more days). This adaptation has been called the second phase of cold hardening. To determine mechanisms involved in second phase cold-hardening, apoplastic fluid was extracted and analyzed from the crown tissue of a winter-hardy oat. Apoplastic fluid from non-hardened, first phase hardened (+3C for 3 weeks) and second phase hardened crown tissues had low levels of symplastic contamination as determined by malate dehydrogenase activity. An analysis of the apoplastic fluid from crowns of first phase and second phase hardened plants by SDS-PAGE showed significant induction of polypeptides of sizes 6.2 KD and 16.4 KD. Further characterization of these polypeptides is in progress. In addition, levels of fructan, sucrose, glucose and fructose as well as the activity of invertase and fructan exohydrolase in the apoplast increased significantly above that in non-hardened and first phase hardened plants. The increase in concentration and activity of numerous compounds in the apoplast suggests several mechanisms may be responsible for an increase in the freezing tolerance of second phase hardened plants.