Glutathione transferase, but not agglutinin, is a dormancy-related protein in Castanea crenata trees

The annual changes in Japanese chestnut (Castanea crenata Sieb. et Zucc.) agglutinin (CCA) were investigated by both protein and RNA blotting analyses, to clarify whether CCA has a function as storage protein. In the woody part of shoots and leaves, CCA expression was only detected at both the protein and RNA levels in May and June. In buds, the CCA protein and mRNA expressions were both restricted to April. However, the amount of accumulated CCA was too low to act as a nitrogen reserve. No expression was observed in the bark at any time point, suggesting that bark does not contain either CCA or CCA-like proteins. These results suggest that CCA may be required in young organs as a defense protein, rather than as a storage protein. In addition, CCA was not related to dormancy, unlike some other woody plant bark lectins. In contrast to CCA, a 28 kDa polypeptide was observed to accumulate during dormancy. Sequence analysis indicated that this polypeptide was a glutathione transferase. After cDNA cloning, RNA blot analyses indicated that this glutathione transferase was strongly expressed in woody parts during mid-winter. In shoots, this protein represented approximately 10% of the total soluble protein content. Therefore, in Japanese chestnut trees, glutathione transferase may play a nitrogen storage role in addition to its intrinsic defensive role against stresses during dormancy.