[Alleviative effects of nitric oxide on the biological damage of spirulina platensis induced by enhanced ultraviolet-B].

Continuing depletion of the stratospheric ozone layer by atmospheric pollutants, in particular chlorofluorocarbons (CFCs), has resulted in an increasing incidence of solar UV-B (280-320 nm) at the Earth's surface. Enhanced UV-B radiation has been considered as important global environmental problem and results in important effects to mankind and the entire global ecosystem. Nitric oxide (NO) is not only a toxic molecule, one of reactive nitrogen species (RNS), but also an important redox-active signaling molecule. NO is really a double-edged sword, it can be either beneficial and activate defense responses in plants and animals or toxic, together with ROS. Besides those, NO can also act as a signal molecule and play very important roles in life of organisms. To study the effects of NO on the biological specific property of enhanced UV-B stressed Spirulina platensis, the chlorophyll-a, protein contents and biomass were investigated under enhanced UV-B radiation and its combination with different chemical treatment. The changes of chlorophyll-a, protein contents and biomass confirmed that 0.5 mmol/L sodium nitroprusside (SNP), a donor of nitric oxide (NO), could markedly alleviate the biological damage of cyanobacteria-Spirulina platensis 794 caused by enhanced ultraviolet-B. Further results proved that NO significantly increase the content of protein and proline. Meanwhile, the accumulation of reduced glutathione (GSH) in S. platensis cells were raised under normal growth condition. But exogenous NO could decrease the increasing of reduced glutathione (GSH) in enhanced UV-B stressed S. platensis cells. These results suggest that NO has protective effect and can strongly alleviate biological damage caused by UV-B stress in S. platensis 794 cells. For the first time, reported the effect of NO on the regulating ability of biological damage of S. platensis induced by enhanced UV-B. Therefore, further investigations will be necessary to inquire into the interaction and inter-correlation of signal molecules and the mechanism in cyanobacterium under enhanced UV-B stress.

Relation of several antioxidant enzymes to rapid freezing resistance in suspension cultured cells from alpine Chorispora bungeana.

Chorispora bungeana Fisch. & C.A. Mey (Crucifer) is a rare alpine subnival plant surviving sudden snowstorms. In this paper, we have attempted to explore possible roles of autoxidation rate (AR) and the antioxidant enzymes associated with cryoprotective mechanisms in the plant cells. The results showed that when the suspension cultures growing at 25 degrees C were suddenly exposed to -8 degrees C for 15 days, 2,3,5-triphenyltetrazolium chloride reduction was not affected within 9 days and AR remained at a low level in comparison with controls. This indicated that the cells maintained considerable amounts of soluble protein and the integrity of the cell membranes was intact during the whole freezing test. Furthermore, on average, the activity of antioxidant enzymes such as superoxide dismutase, dehydroascorbate reductase, ascorbate peroxidase and glutathione reductase were prominently enhanced in the freezing-stressed cells. Peroxidase activity significantly increased soon after freezing, possibly to make up for the early decrease of catalase activity in the cells. Statistical analysis showed negative correlations between resistance to rapid freezing and antioxidant enzyme activity in the cultured cells after exposure from 25 to -8 degrees C, indicating that the reduction of cell viability with freezing activates a combination of antioxidant enzymes that results in intact cells. All of these findings suggest a synergy between these antioxidant enzymes, leading to a low autoxidation rate that contributes to the protection of the cell membranes and plays an important role in the resistance of suspension cultured cells of C. bungeana to sudden freezing.