Dehydrin Gene Expression and Leaf Water Potential Differs between Spring and Winter Cereals During Cold Acclimation

Spring and winter cultivars of wheat (Triticum aestivum L.) and rye (Secale cereale L.) were cold acclimated using controlled environment and natural conditions. With respect to freezing tolerance, winter cereal seedlings could be distinguished from their spring counterparts by their initiation of acclimation at a warmer temperature, increasing in freezing tolerance sooner, and by achieving greater freezing tolerance at the end of the acclimation period. The timing and extent of expression of a family of dehydrin genes correlated with the increase in measured freezing tolerance in both spring and winter genotypes. The expression of these genes was detected sooner in the winter types, and dehydrin mRNA accumulated to higher levels in the winter cereals. Dehydrin transcripts could be detected throughout the acclimation period in winter cereals, but were only moderately expressed in spring cereals in response to acclimation. Similar results were obtained using western blot analysis with a dehydrin carboxy terminal antibody. Crown moisture content (CMC), crown osmotic potential (COP) and leaf water potential decreased in spring and winter cereals in response to acclimating conditions in both controlled environment and field conditions, but were lowest in fully acclimated winter cereals. However, the onset and rate of decrease in CMC and COP did not differ between the spring and winter genotypes, suggesting that neither CMC nor COP were involved in the initial regulation of dehydrin gene expression. Leaf water potential (LWP) also declined at similar rates in the spring and winter cereals in the field between September and November. However, a difference in LWP was observed between spring and winter wheat subjected to a cold shock treatment. The winter genotype LWP decreased within 10 h of exposure to 2 °C, reached significantly lower levels than prior to the cold shock, but returned to pre cold-shock level after 7 days at 2 °C. In contrast, the decline in leaf water potential in spring wheat was slower and less pronounced than in winter wheat. These results correlate well with those observed with dehydrin gene expression and suggest a relationship between water potential and cold-induced gene expression.