Cd^(2+)胁迫条件下椭圆小球藻的生理应答

PHYSICAL RESPONSES TO Cd^(2+) STRESS IN CHLORELLA ELLIPSOIDEA

研究了一株高重金属抗性的椭圆小球藻在Cd2 + 胁迫下的生理变化 ,结果显示 ,在 10— 2 4 0 μmol/L浓度的Cd2 +胁迫下 ,随着金属离子浓度提高 ,叶绿素的总量减少 ,光合放氧受到抑制。Cd2 + 离子浓度的提高 ,导致了氧自由基的大大增加 ,同时脯氨酸、SOD(超氧化物歧化酶 )以及POD(过氧化物酶 )水平均大大提高。结果提示这些与消除自由基有关的代谢产物的积累 ,有利于细胞减少胁迫造成的损伤。CAT(过氧化氢酶 )对Cd2 + 离子是敏感的 。

A high heavy metal resistant Chlorella ellipsoidea strain was isolated from the electroplating waste water.Former researches had showed the alga had high tolerance to heavy metals and was able to eliminate Cu 2+ ,Zn 2+ ,Ni 2+ and Cd 2+ effectively from water.So it could be used for decreasing heavy metal pollution.To understand the physical mechanisms of the alga against the toxicities of heavy metals,we studied the physical responses of the alga to Cd 2+ stress.In this research,we focused on the physical reactions to radical injuring in cells caused by Cd 2+ . Methods:Photosynthesis O 2 release was measured by membrane oxygen electrode;Superoxide anion radical was measured by xanthine oxidase and NBT system;Superoxide dismutase (SOD) activity is determined by hydroxylamine assay-developed from xanthine oxidase assay;Catalase(CAT)was measured by molybdic acid method;Peroxidase(POD)was determined by method of guaiacol oxidation;Proline was measured by the method of Sulosalicylic acid. Results:Chlorophyll content and photosynthetic O 2 release were measured as indicators of cadmium toxicities.Results showed that,between 10 to 240μmol/L Cd 2+ ,total chlorophyll content and photosynthesis O 2 release decreased when the ion concentration increased.The lower concentration of Cd 2+ ,10μmol/L induced higher chlorophyll-a,it was 130% of the control.Cadmium caused the ratio of chlorophyll-a/b rising. When Cd 2+ was over 30μmol/L,the ratio of chla/b rose from 1 22 to 2 61 These showed Cd 2+ in this concentration range could cause toxicities to the C.ellipsoidea. So this concentration range of Cd 2+ was used as stress to induce radicals and observe the physical responses of the alga.Results showed Cd 2+ produced more O 2-. in algal cells.When Cd 2+ was 90μmol/L,O 2-. was 2.07 times as much as the control in 72hrs after incubated.Meanwhile,POD was induced strongly and reached the highest level.It's content was 4.84 times concentration of the control.But for 120μmol/L and 240μmol/L Cd 2+ ,POD content was 4 10 and 3 63 times respectively;There were four SOD isoenzyme bands in the electrophoresis gel.The least molecular band was Fe-SOD,and the other three were Mn-SOD.Highest SOD content was induced by 120μmol/L Cd 2+ ,reached 1 3 times as much as the control.Two types of SOD showed different responses to cadmium stress.Mn-SOD obviously increased.That caused total amount of SOD increasing.But Fe-SOD decreased;Proline content and Cd 2+ concentration in algal cells was correlated.When Cd 2+ was 10μmol/L,proline content was 1 89 times of the control.Proline reached highest level,2.86 times of the control in 120μmol/L Cd 2+ .These results suggested that increasing of free radical elimination enzymes and substances was helpful to the algae to resistant cadmium injuring.However,as one of the most important anti-oxidation enzymes,CAT showed an opposite response to the Cd 2+ .Its content went down with Cd 2+ going up.When Cd 2+ was 90μmol/L,CAT activity was 23.36% of the control.This meant CAT was very sensitive to Cd 2+ . Conclusion:Cd 2+ could induce radicals which were toxic to algal cell.The high heavy metal resistant C.ellipsoidea strain could produce more SOD,POD and proline to decrease the injuries.