Expression of the barley dehydrin multigene family and the development of freezing tolerance

Dehydrins (DHNs; LEA D11) are one of the typical families of plant proteins that accumulate in response to dehydration, low temperature, osmotic stres s or treatment with abscisic acid (ABA), or during seed maturation. We prev iously found that three genes encoding low-molecular-weight DHNs (Dhn1, Dhn 2 and Dhn9) map within a 15-cM region of barley chromosome 5H that overlaps a QTL for winterhardiness, while other Dhn genes encoding low- and high-mo lecular-weight DHNs are located on chromosomes 3H, 4H and 6H. Here we exami ne the expression of specific Dhn genes under conditions associated with ex pression of the winterhardiness phenotype. Plants grown at 4 degrees C or i n the field in Riverside, California developed similar, modest levels of fr eezing tolerance, coinciding with little low-MW Dhn gene activity. Dicktoo (the more tolerant cultivar) and Morex (the less tolerant) grown in Saskato on, Canada expressed higher levels of expression of genes for low-MW DHNs t han did the same cultivars in Riverside, with expression being higher in Di cktoo than Morex. Dehydration or freeze-thaw also evoked expression of gene s for low MW DHNs, suggesting that the dehydration component of freeze-thaw in the field induces low expression of genes encoding low-MW DHNs. These o bservations are consistent with the hypothesis that the major chilling-indu ced DHNs help to prime plant cells for acclimation to more intense cold, wh ich then involves adaptation to dehydration during freeze-thaw cycling. A r ole for chromosome SH-encoded DHNs in acclimation to more intense cold seem s possible, even though it is not the basis of the major heritable variatio n in winterhardiness within the Dicktoo x Morex population.