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 cont rol and cold conditions. Freezing injury was less in cold-acclimated leaves than in control leaves. In cold-acclimated leaves, the freezing injury inc reased when apoplastic solution is extracted. In addition, ice nucleation a ctivity was lower with apoplastic proteins extracted from cold-acclimated l eaves than from control leaves. These results suggest that the proteins pre sent in the apoplast during cold acclimation are an important component of the mechanism by which cabbage and winter wheat leaves inhibit extracellula r ice formation. Winter wheat has greater freezing tolerance than cabbage b ecause winter wheat leaves have lower freezing injury and apoplastic protei ns in winter wheat leaves have lower ice nucleation activity. (C) 1999 Else vier Science Ltd. All rights reserved.