Dehydrin-like proteins in castor bean seeds and seedlings are differentially produced in response to ABA and water-deficit-related stresses

The stress inducibility of dehydrin protein production in seedlings of castor bean was analysed by subjecting them to ABA and various water-deficit-related treatments including desiccation, water stress, high salt, high osmolarity, and low temperature. A further goal was to determine whether the immature seed (at stages prior to major dehydrin synthesis) would respond in a similar manner to these stresses. A number of dehydrin-like proteins increased in seedlings subjected to the various stress treatments. In the endosperm, these appear to be different from the dehydrin-related polypeptides that are induced during late seed development and which persist following germination/growth of mature seeds. In the endosperm of seedlings, ABA, water stress and desiccation induced the same dehydrin polypeptides, while high osmolarity, high salt and low temperature induced a different set. Stress-specific differences in dehydrin synthesis were also found in the cotyledons and radicle of castor bean seedlings; however, dehydrins inducible by exogenous ABA were consistently produced. Immature seeds treated with ABA or subjected to stress responded by producing dehydrin-like proteins associated with late development; however, the same proteins were induced following detachment of immature seeds from the parent plant and maintenance on water. When seedlings were exposed simultaneously to GA and either ABA, high salt, or low temperature, dehydrin production was suppressed. It is concluded that dehydrin production in castor bean is tissue-specific and is dependent upon the physiological stage of the seed. In the endosperm, the response to different stresses may rely upon more than one signal transduction pathway.