Effect of apoplastic proteins on freezing tolerance in leaves

Freezing tolerance was determined in cabbage (Brassica oleracea cv Acephala) and winter wheat (Triticum aestivum cv Dogu-88) leaves growing under control and cold conditions. Freezing injury was less in cold-acclimated leaves than in control leaves. In cold-acclimated leaves, the freezing injury increased when apoplastic solution is extracted. In addition, ice nucleation activity was lower with apoplastic proteins extracted from cold-acclimated leaves than from control leaves. These results suggest that the proteins present in the apoplast during cold acclimation are an important component of the mechanism by which cabbage and winter wheat leaves inhibit extracellular ice formation. Winter wheat has greater freezing tolerance than cabbage because winter wheat leaves have lower freezing injury and apoplastic proteins in winter wheat leaves have lower ice nucleation activity. (C) 1999 Elsevier Science Ltd. All rights reserved.