Four immunologically related proteins that belong to the annexin family wer
e identified in cold acclimated wheat (Triticum aestivum). Two soluble form
s with molecular masses of 34 and 36 kDa were found to bind phospholipid me
mbranes in a calcium-dependent manner. These two forms are similar to the p
reviously reported doublet in several plant species. The other two forms, w
ith molecular masses of 39 and 22.5 kDa, were found associated with the mic
rosomal fraction. Biochemical analysis showed that both forms are intrinsic
membrane proteins and their association with the membrane is calcium indep
endent. This is, to our knowledge, the first report of the presence of thes
e annexin forms in plants. Membrane purification by two phase partitioning
demonstrated that the p39 form is localized to the plasma membrane. Immunob
lot analysis showed that the protein level of both p39 and p22.5 increases
gradually reaching a maximum level after one day of low temperature exposur
e. The protein accumulation was similar in both hardy and less hardy cultiv
ars, suggesting that the accumulation is not correlated with freezing toler
ance. The results are discussed with respect to the possible role of these
new intrinsic membrane annexins in low temperature signal transduction path
way.