Comparative Studies On Adaptability Of Cyanobacteria To Environment Stress In The Lake Of Qinghai-Tibet Plateau

Qinghai-Tibet Plateau is one of the area where more sensitive to the change in global climate, which is the typical extreme environments. The cyanobacteria grow in the lake of Qinghai-Tibet Plateau have evolved a number of mitigation strategies/defense mechanisms to reduce the damaging effects caused by UV-B after a long time adaptation and natural selection. Cyanobacteria not only was suffer from environmental stress, but also has formed the typical features of physiological, biochemical and morphological structure for the adaptations. UV-B and temperature have an important effects on the characteristics of physiological and biochemical of plant. The effects of UV-B on the growth and biochemistry of plants and algae have been reported in many papers, but few of them about cyanobacteria,especially, the research report on the response and adaptation mechanism of cyanobacteria to enhanced UV-B in high altitude aquatic ecosystem still is blank. Therefore, the cyanobacteria isolated from Qinghai Lake were used as experiment materials(Oscillatoria sp. X11,Chroococcus sp. X12) and the low altitude cyanobacteria(Oscillatoria sp. FACHB-528,Chroococcus sp. FACHB-193) as the comparison to study the growth, physiological,biochemistry, ultrastructure and adaptability of the Qinghai Lake cyanobacteria under long-term UV-B radiation and stress temperature. This study has important theoretical value and practical significance for protectingthe ecological environment of Qinghai-tibet plateau and revealing the response of cyanobacteria to adverse stress. The purpose of this study is to provide the scientific guidance for further carrying on the same research in this field. The research results in this study are as follows:1. There were 5 strains of cyanobacteria had been separated from the samples and there were 2 dominant strains among them had been identified as Oscillatoria sp. and Chroococcus sp. respectively by their physiological and biochemical characteristics and 16 s rDNA features.2. Under laboratory conditions, 4 kinds of algae(Oscillatoria sp. X11, Chroococcus sp.X12, Oscillatoria sp. 528, Chroococcus sp. 193) were taken as research materials to take related experimental treatment, the research results are as follows:(1) After 37℃ heat stress, the research results showed that the biomass, phycocyanin,allophycocyanin, chlorophyll content decreased. The SOD, POD activity were decreased at the early then increased with the prolonged treatment time. the proline and MDA content increased. Significance of difference of 4 cyanobacteria between stress temperature treatment and control had reached a significant or extremely significant level. The influence of heat stress on 528 and 193 was higher than X11 and X12, the effects were different between the materials.(2) Natural low temperature(4℃) stress, the results showed that the biomass,phycocyanin, allophycocyanin, chlorophyll content decreased. The SOD, POD activity were decreased at the early then increased with the prolonged treatment time. the proline and MDA content increased. Compared with the controls, the differences between the treatment and the control has reached a significant or extremely significant level. Low temperature stress caused the algae advance into dormancy, so the damage of low temperature stress to cells was slightly. The impact of 37℃ and 4℃ on 528 and 193 were more severe than X11 and X12. It reflected that the cyanobacteria come from Qinghai Lake has better adaptation to adverse stress.(3) Supplementary irradiation(time was 4 h: from 10:00 to 14:00) was with UV-B intensity of 2.4 W·m-2 per day respectively. The results showed that the biomass of Qinghai Lake cyanobacteria gradually decreased, scytonemin and flavonoids increased, MAAs,phycocyanin drastically reduced at early treatment then remained relatively unchanged over time at UV-B irradiation. The photosynthetic pigment of 528 and 193 significantly decreased,MAAs, scytonemin and flavonoids reduced. And the cells were severely damaged under the UV-B radiation. The difference between control and treatment was reached a significant or extremely significant level. UV-B caused changes in the ultrastructure of cells after exposure for 13 days, such as destructed thylakoids, deformed and swollen cells. The results indicated that Qinghai Lake cyanobacteria X11 and X12 had better adaptation to 2.4 W·m-2 intensity of UV-B radiation, and 528 and 193 were more sensitive to 2.4 W·m-2 intensity of UV-B.From all above, the cyanobacteria come from Qinghai Lake showed more adaptation to UV-B radiation than the cyanobacteria come from low altitude after treatment either in temperature stress(4℃ and 37℃) or 2.4 W·m-2 intensity of UV-B radiation(1,3,5,7,9,11,13 d)treatment, which demonstrated that Qinghai Lake cyanobacteria X11 and X12 have formed stronger adaptation mechanism to environment stress than 528 and 193. The differences between the control and all the treatment varieties have reached a significant or extremely significant level by T-test. The correlation analysis of physiological and ecological factors indicators also showed that X11 and X12 have developed strong resistance under long-term domestication and natural selection. Meanwhile, the changes of ultrastructure and physiological-biochemical characteristics revealed that the response and adaptive mechanism of Qinghai Lake cyanobacteria to environment stress.