Purification and partial characterization of a dehydrin involved in chilling tolerance during seedling emergence of cowpea

Dehydrins are a family of proteins (LEA [late-embryogenesis abundant] D11) commonly induced by environmental stresses associated with low temperature or dehydration and during seed maturation drying. Our previous genetic studies suggested an association of an approximately 35-kD protein (by immunological evidence a dehydrin) with chilling tolerance during emergence of seedlings of cowpea (Vigna unguiculata) line 1393-2-11. In the present study we found that the accumulation of this protein in developing cowpea seeds is coordinated with the start of the dehydration phase of embryo development. We purified this protein from dry seeds of cowpea line 1393-2-11 by using the characteristic high-temperature solubility of dehydrins as an initial enrichment step, which was followed by three chromatography steps involving cation exchange, hydrophobic interaction, and anion exchange. Various characteristics of this protein confirmed that indeed it is a dehydrin, including total amino acid composition, partial amino acid sequencing, and the adoption of alpha-helical structure in the presence of sodium dodecyl sulfate. The propensity of dehydrins to adopt alpha-helical structure in the presence of sodium dodecyl sulfate, together with the apparent polypeptide adhesion property of this cowpea dehydrin, suggests a role in stabilizing other proteins or membranes. Taken together, the genetic, physiological, and physicochemical data are at this stage consistent with a cause-and-effect relationship between the presence in mature seeds of the approximately 35-kD dehydrin, which is the product of a single member of a multigene family, and an increment of chilling tolerance during emergence of cowpea seedlings.