Relation of Expression of Dehydrins to Their Function
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.
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