Relation of Expression of Dehydrins to Their Function

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The differences in stress specificity and spatial distribution of dehydrins suggest a functional specialization for the members of this protein family. Dehydrins, as well as being important for cell survival during stress, may play an osmoregulatory role in certain cell-types in the absence of stress. The presence of constitutively expressed dehydrins has been reported in various plant species. Examples are pea B61, which is an SK2 type, and Craterostigma plantagineum DSP16, which is a YSK2 type dehydrin (Robertson and Chandler, 1994; Schneider et al., 1993). Constitutive dehydrin-like proteins have also been reported in birch (16 kDa), poplar (50 kDa) and dogwood (60 kDa) (Rinne et al., 1999; Wisniewski et al., 1999). Some constitutively expressed dehydrins are also stress-responsive. For example, Arabidopsis RAB18 (YSK-type) dehydrin, present in the nuclei of guard cells under normal conditions, is also present in the cytosol under stress. Similarly, stress-induced promoter activity in stomatal guard cells has been reported for C. plantagineum DSP16 (Taylor et al., 1995) and tomato TAS14 (Parra et al., 1996), both of which are also YSK-type dehydrins. Stress-induced accumulation of five dehydrins in Arabidopsis (COR47, LTI29, ERD14, LTI30 and RAB18), after treatments with low temperature, ABA and high salt concentration, was characterized immunologically with protein-specific antibodies (Nylander et al., 2001). The dehydrins exhibited clear differences in their accumulation patterns in response to different stressors. LTI30 dehydrin was not detected in unstressed plants. ERD14 (SK2) accumulated in unstressed plants, although the protein level was up-regulated by ABA, salinity and low temperature. LTI29 (SK3) accumulated mainly in response to low temperature, but was also found in ABA- and salt-treated plants. LTI30 (K6) and COR47 (SK3) accumulated primarily in response to low temperature, whereas RAB18 (Y2SK2) was only found in ABA-treated plants and was the only dehydrin in this study that accumulated in dry seeds.