| Abstract: | Ultraviolet-B and heat shock (HS)1) induced changes in growth kinetics, NO?3 reductase (NR), glutamine synthetase (GS), NO?3 uptake and NO?2 efflux activities, have been studied in the wild type Anacystis nidulans and its UV-HS1 strain. The application of UV-B and HS stresses either used separately or in combination shows a drastic changes in growth rates of wild type, and insignificant effect on the growth of the UV-HSt strain. The wild type cells, in contrast to its UV-HSt strain exhibits insignificant effect on NR and GS activities upon UV-B radiation followed by heat shock treatment. Similar treatments to the wild type cells resulted in maximum reduction of NR and GS activities. The NO?3 uptake and NO?2 efflux activities are found to be lower in the UV-HSt strain than in the wild type counterpart and both the systems consisted of an initial rapid phase followed by a slower one. NH+4 grown cells when transferred to NO?3 medium in presence of streptomycin showed significant inhibition in the development of both the NO?3 uptake and NO?2 efflux systems indicating that de novo protein synthesis is required for the development of NO?3 uptake and NO?2 efflux systems. Whereas the same cells in the presence of L-methionine-DL-sulfoximine (MSX) showed marginally higher NO?3 uptake but, exhibits only 42% NO?2 efflux to that of MSX-devoid both the cells. It is suggested that NH+4 assimilation via GS is necessarily required for NO?2 efflux system to be functional. |
