Cr^(6+)胁迫对莱茵衣藻光合作用的影响

Photosynthesis of Chlamydomonas reinhardtii under Cr^(6+) Stress

以莱茵衣藻(Chlamydomonas reinhardtii)为研究材料,采用氧电极和快速叶绿素a荧光诱导动力学方法研究了不同浓度和时间Cr6+处理对其光合作用的影响。结果表明:当Cr6+浓度大于40μmol/L时,莱茵衣藻细胞数逐渐下降,而藻细胞变大;表观光合速率成为负值,呼吸作用随Cr6+处理浓度的增加先上升后下降至对照水平;莱茵衣藻有活性放氧复合体比例随Cr6+处理浓度的增加逐渐降低,80μmol/L Cr6+处理3 d时已下降至13.72%;光合驱动力(DFABS)随Cr6+浓度增加逐步下降,并以DFφPo在DFABS的下降中的贡献最大。研究发现,重金属Cr6+胁迫显著影响莱茵衣藻的光合作用,而对呼吸作用则影响较小;Cr6+主要通过损伤供体侧的放氧复合体以及阻断QA至QB的电子传递而抑制光系统Ⅱ的功能;莱茵衣藻光系统Ⅱ对Cr6+处理比较敏感且存在着多个作用位点,并首先影响反应中心光能捕获效率,其次影响反应中心的活性,最后影响QA-之后的电子传递。

The primary site and inhibition mechanism was investigated by Clark-type electrode and chlorophyll a fluorescence induction kinetics with concentration and time changed when Chlamydomonas reinhardtii was exposed to hexavalent chromium.The number of C.reinhardtii cells gradually decreased,while the algal cell larger when the Cr6＋ concentration is more than 40 μmol/L.Photosynthetic rate decrease to negative,respiration rate increased with the concentration increased and then decreased to control level;Fast chlorophyll a fluorescence induction kinetics showed that the ratio of C.reinhardtii active oxygen evolving complex decreased with Cr6＋ increasing,80 μmol/L Cr6＋ handling three days has been reduced to 13.72%.Drive force（DFABS） gradually decreased with the Cr6＋ concentration increasing.The path analysis showed that the decline in DFφPo in DFABS make the greatest contribution.These results show that heavy metals Cr6＋ primarily inhibited photosynthesis,but rarely effected on respiration.Cr6＋ inhibited photosystem Ⅱ mainly through damaging the donor of oxygen evolving complex and blocking the QA-to QB-electron transfer.This study demonstrated that PSⅡ of C.reinhardtii was more sensitive and had several action sites to Cr6＋ treatment over time change.Inhibitory effect would be changed with the time of Cr6＋ treatment,the efficiency of trapped energy per reaction center affected at first,followed by the activity of reaction center,finally impact on the electron transport chain beyond QA-.