Dehydrins in cold-acclimated apices of birch ( Betula pubescens Ehrh.): production, localization and potential role in rescuing enzyme function during dehydration

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 alpha-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.

Linking the Salt Transcriptome with Physiological Responses of a Salt-Resistant Populus Species as a Strategy to Identify Genes Important for Stress Acclimation

“…Dehydrins that occur immediately in roots but only late in leaves have been shown to maintain a highly disordered status under high solute concentrations where globular proteins would collapse (Mouillon et al, 2006). They may also act as protein cryoprotectants (Hara et al, 2001;Seki et al, 2002) and contribute to protection from drought stress (Rinne et al, 1999;Wang et al, 2004). The time courses observed here suggest a protective function of dehydrins against ionic disorders (Mouillon et al, 2008), whereas the delayed activation of osmotins, another class of well-known stress-activated genes (Shinozaki and Yamaguchi-Shinozaki, 2007), indicates that these proteins must be involved in helping the plant to cope with life at a new level of cellular homeostasis.…”

Proteomics Approach to Identify Dehydration Responsive Nuclear Proteins from Chickpea (Cicer arietinum L.)

“…Dehydrins have been proposed to have a protective function during abiotic stress via a number of different mechanisms. These include improving or protecting enzyme activity under cold or dehydration conditions (83,84); or acting as radical scavengers (85) or as membrane stabilizers (81,86). Vicilin (CaN-656) and conglutin (CaN-17) are basically storage proteins, which possess a lectin-type activity.…”

Genetic approaches towards overcoming water deficit in plants - special emphasis on LEAs

“…DHNs found only in the cytosol include those of C. plantagineum DSP16 (Schneider et al, 1993) and rice RAB21 (Mundy and Chua, 1988). DHNs in birch improve enzyme activity under conditions of low water activity and were found localized in storage protein bodies and starch rich amyloplasts (Rinne et al, 1999).…”