Dehydrins in cold-acclimated apices of birch (Betula pubescens Ehrh.): production, localization and potential role in rescuing enzyme function during dehydration |
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| Authors: | Päivi L H Rinne Päivi L M Kaikuranta Linus H W van der Plas Chris van der Schoot |
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| Institution: | (1) Department of Plant Physiology, Wageningen Agricultural University, Arboretumlaan 4, NL-6703 BD Wageningen, The Netherlands, NL;(2) Department of Biology, University of Oulu, P.O. Box 3000, FIN-90401 Oulu, Finland, FI;(3) ATO-DLO, Bornsesteeg 59, P.O. Box 17, NL-6700 AA Wageningen, The Netherlands, NL |
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| Abstract: | Dehydrins accumulate in various plant tissues during dehydration. Their physiological role is not well understood, but it
is commonly assumed that they assist cells in tolerating dehydration. Since in perennials the ability of the shoot apex to
withstand dehydration is pivotal for survival through winter, we investigated if and how dehydrins may be involved. A first
step in assessing such a role is the identification of their subcellular location. We therefore mapped the location of dehydrin
homologues, abscisic acid-responsive (RAB 16-like) polypeptides, in the apex of birch (Betula pubescens Ehrh.). In non-cold-acclimated plants a single low-abundant RAB 16-member (a 33-kDa polypeptide) was produced, and localized
in the cytoplasm only. During cold acclimation two additional members were produced (24 and 30 kDa) and accumulated in nuclei,
storage protein bodies and starch-rich amyloplasts. Western blots of proteins isolated from purified starch granules and from
protein bodies revealed the presence of the 24-kDa dehydrin. Since starch and protein reserves are gradually consumed during
winter, serving cell maintenance, starch- and protein-degrading enzymes must remain locally active. We therefore investigated
the hypothesis that dehydrins might create local pools of water in otherwise dehydrated cells, thereby maintaining enzyme
function. In agreement with our hypothesis, enzyme assays showed that under conditions of low water activity a partially purified
dehydrin fraction was able to improve the activity of α-amylase (EC 3.2.1.1.) relative to fractions from which dehydrin was
removed by immunoprecipitation. The results confirm the general belief that dehydrins serve desiccation tolerance, and suggest
that a major function is to rescue the metabolic processes that are required for survival and re-growth.
Received: 12 September 1998 / Accepted: 19 April 1999 |
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| Keywords: | :α -Amylase Dehydrin Desiccation tolerance Freezing tolerance LEA proteins RAB proteins |
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