EFFECTS OF HYPERHALINE STRESS ON THE PHYSIOLOGICAL AND BIOCHEMICAL CHARACTERISTICS OF NOSTOC COMMUNE AND NOSTOC SPHAEROIDES

Nostoc commune is a terrestrial Nostoc species with high desiccation tolerant ability, while Nostoc sphaeroides is an aquatic ones.Their reactions to salt stress might be different for the adaptation to their habitats. In order to clarify the differences, the effects of hyperhaline stress on their photosynthesis, contents of soluble carbohydrates, proline and plasmalemma permeability were investigated. Photosynthesis was significantly inhibited when the Nostoc species were submerged in salty water. Net photosynthesis could still be detected in N. commune after incubating in salty water for 48,96h at the concentrations of 0.6 and 0.8mol稬-1 .However, it could not be detected in N.sphaeroides at the same conditions. In Nostoc commune, the contents of proline and soluble carbohydrates increased when treated with increased NaCl concentrations to 0.8mol稬-1,and the increases of soluble carbohydrate ranged from 87% to 200%, and the plasmalemma permeability increased with increased NaCl levels till 0.4mol稬-1 .In Nostoc sphaeroids, proline decreased, but soluble carbohydrates showed a straight increase with the elevated level of salt when submersed in NaCl solutions of less than 0.4mol稬-1 and the increases ranged from 100% to 1000%, but decreased with higher NaCl concentrations and plasmalemma permeability showed a straight increase with the elevated level of salt concentration. The plasmalemma permeability could reach above 90% in N.sphaeroides when the salt concentrations were 0.6 and 0.8mol稬-1,however, it was only 31% and 37% for N.commune. The results indicated that N.commune was more tolerant to salt stress compared with N.sphaeroides. Soluble carbohydrates might act as an important role in resisting salt stress in N.commune and N.sphaeroides, however,it was impossible for proline to be a compatible solute in resisting salt stress in N.sphaeroides.