Two novel intrinsic annexins accumulate in wheat membranes in response to low temperature

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.