Isolation and characterization of a jacalin-related mannose-binding lectinfrom salt-stressed rice (Oryza sativa) plants

A novel plant lectin was isolated from salt-stressed rice (Oryza sativa L.) plants and partially characterized. The lectin occurs as a natural mixture of two closely related isoforms consisting of two identical non-covalently linked subunits of 15 kDa. Both isoforms are best inhibited by mannose and exhibit potent mitogenic activity towards T-lymphocytes. Biochemical analy ses and sequence comparisons further revealed that the rice lectins belong to the subgroup of mannose-binding jacalin-related lectins. In addition, it could be demonstrated that the lectins described here correspond to the pr otein products of previously described salt-stress-induced genes. Our resul ts not only identify the rice lectin as a stress protein but also highlight the possible importance of protein-carbohydrate interactions in stress res ponses in plants.