Superoxide dismutase-like protein from roots of the intermediate C 3-CAM plant Mesembryanthemum crystallinum L. in in vitro culture

Abstract

The facultative halophyte Mesembryanthemum crystallinum can shift its mode of carbon assimilation from C 3-pathway to CAM (crassulacean acid metabolism) in response to salinity. The effect of salt-induced stress on antioxidative enzyme superoxide dismutase (SOD) in leaves of M. crystallinum was studied previously in in vivo conditions ‘Plant Cell Environ. 21 (1998) 169’. We have demonstrated that NaCl-induced C 3-CAM transition takes place in plants cultured in vitro. The same SOD forms were identified in leaves and roots of plants cultured in vitro. In M. crystallinum roots, additionally to ‘leaf form’ of MnSOD (MnSOD I) another MnSOD-like form (MnSOD II) was detected. The estimated native molecular mass of MnSOD II is in range of 186–201 kDa (native gradient electrophoresis) and 93 kDa (gel filtration). The subunit mass is estimated to be about 57 kDa. The new SOD-like form exhibits a high thermal stability and resistance to a reducing factor, mercaptoethanol. It is suggested that MnSOD II form can exist as active aggregates. In salt-induced CAM mode of photosynthesis the activity of MnSOD I and Cu/ZnSOD increases significantly, while the activity of the new MnSOD-like protein does not change. The potential physiological role of the MnSOD II is discussed.