GAMMA-IRRADIATION DAMAGE TO THE TONOPLAST IN CULTURED SPINACH CELLS

The effects of gamma-irradiation on the tonoplast of cultured spinach cells were investigated using purified tonoplast vesicles. The activit ies of the membrane-bound enzymes, i.e. ATPase and pyrophosphatase (PP ase), were considerably reduced when the isolated vesicles were expose d to radiation (1 and 5 kGy), but this reduction was alleviated in the tonoplast irradiated in vivo, In the presence of an extract prepared from non-irradiated cells, the decrease of the enzyme activities in th e irradiated vesicles was reduced. Similar alleviation effects were al so observed with regards to fatty acid residues of membrane lipids as well as with SDS-PAGE detectable polypeptides of the membrane. From th ese results, we conclude that the tonoplast in vivo was protected from radiation at least partly through the action of certain metabolic pro duct(s). Other noticeable features clarified in this investigation are : (1) ATPase is more susceptible to radiation than PPase, (2) unsatura ted fatty acids in membrane lipids were markedly decreased, in contras t to unaltered saturated acids, (3) membrane proteins seem to be more susceptible to radiation as compared to membrane lipids. (C) 1998 Else vier Science B.V. All rights reserved.