Abstract
Freezing resistance of birch (Betula platyphylla L.) xylem tissue is induced during seasonal cold acclimation with the development of supercooling ability. Both intracellular and extracellular components may contribute to the supercooling ability of winter xylem tissue. In this study, identification of winter-induced extracellular proteins (WCWPs) was examined to study the physiological roles of WCWPs in the freezing resistance mechanism of birch xylem tissue.
Extracellular proteins were eluted with acidic solution from xylem tissues of birch twigs harvested in the field. SDS-PAGE analysis showed that the extracellular protein composition changed drastically after seasonal cold acclimation. Levels of proteins with molecular masses of about 30 kDa, namely WCWPs, increased markedly in winter. The N-terminal amino acid sequencing revealed that some of WCWPs are similar to each other and are homologous to a pathogenesis-related protein. Immunoblot analysis also showed the similarity between the WCWPs.
