Responses Of Nostoc Flagelliforme Suspension Cells Under Low-temperature Stress

Nostoc flagelliforme is a kind of terrestrial economic algae, located in the arid and semi-arid area, also found that can grow in low-temperature environment. We use the artificial cultivation Nostoc flagelliforme suspension cells as research materials, through comparative analysis 4℃stress and 20℃culture condition of normal growth state and physiological characteristics change, to explain the mechanism of Nostoc flagelliforme suspension cells to survive in extreme situations. Research results summarized as follows:1. Growing in 4℃stress for 15 days, the morphological characteristics of Nostoc flagelliforme suspension cells changed a little, such as the color of a fraction of cells changed by normal green into yellow and brown, when be observed in the optical microscope 400 times, also relative growth significantly reduced, thus low-temperature stress make metabolism rate of Nostoc flagelliforme suspension cells restrained, lower metabolic rate may be a mean of Nostoc flagelliforme suspension cells to resist low-temperature stress.2. Plasma membrane ion leakage rate under 4℃low-temperature increased obviously on the first and third day, then on the fifth day there were no obvious difference compared to the contrast. The results showed that the relative permeability of plasma membranes under low-temperature environment has a certain tolerance. Further study found that low temperature cause accumulation of intracellular osmoregulation substance, such as trehalose and proline. And the cell accumulated proline and trehalose rapidly inside, which plays an active role during osmotic regulation, reduced the damage of the plasma membrane structure under the low-temperature stress on Nostoc flagelliforme suspension cells, protect and maintain lower freezing point physiological activity substance and function enzyme activity, make the cells have certain tolerance to low-temperature.3. Cell activity under the 4℃low-temperature stress in the first three days dropped, on the fifth days cell activity handle back to the same level with the controls. The results showed that Nostoc flagelliforme suspension cells under low-temperature stress, had the membrane system with stable enzyme activity and efficient transfer electronic, the results from the above that plasma membrane ion leakage rate changes and osmoregulation substance accumulation confirmed this. We speculate that protecting plasma membrane structural integrity is another important means of Nostoc flagelliforme suspension cells to resist low-temperature stress. 4. Nostoc flagelliforme suspension cells under 4℃low-temperature for the first day, third day and fifth day, we found that the value of Fv/Fm and Yield on photosynthetic systemⅡdeclined significantly compared to 20℃, the first of three days down the most significant. These results indicated that the photosynthetic efficiency of Nostoc flagelliforme suspension cells reduced clearly, then 4℃low-temperature stress reduces the primal light capture ability and photosynthetic electronic transmission ability of photosynthetic system II, which has affected the photosynthetic system functions of Nostoc flagelliforme suspension cells. However the content of chlorophyll a under low temperature after 5 days increased comparing to the control, which showed that under low-temperature stress intracellular chlorophyll a content remained at a stable level, to ensure that the photosynthesis.5. We detected that for the first three days and 5 days under 4℃stress, nitrogenase activity of Nostoc flagelliforme suspension cells reduced significantly. The result indicated that nostoc nitrogen-fixing ability declined under low-temperature stress.6. SOD enzyme activity determination and active electrophoresis results showed that 4℃low-temperature processing 1 day, three days and 5 days, SOD enzyme activity increased. That started the super oxide enzyme antioxidant capacity of Nostoc flagelliforme suspension cells. Under low-temperature condition, Nostoc flagelliforme suspension cells ros generation and inside cells originally in the dynamic balance of clear state is broken, Nostoc flagelliforme suspension cells improved SOD activity (SOD) to remove a lot of ros producing continually, to protect the photosynthetic organ, membrane and biological macromolecules.In summary, Nostoc flagelliforme in unique ways to adapt to low temperature environment. Nostoc flagelliforme has its unique morphological characteristics, physiological and biochemical and antioxidant defense mechanism. It is extreme precious microbial resources in nature, and suspension cells of Nostoc flagelliforme can be ideal material. Whether trehalose fight microtherm process of stress, and its metabolites of metabolic pathways and function of the molecular mechanisms, will be our next interested work in focus.