盐度降低对长心卡帕藻原初光化学反应的影响

The changes of primary photochemical reactions in Kappaphycus alvarezii exposed to low salinity

为探讨大量降雨如何导致热带产胶海藻长心卡帕藻死亡,通过快速叶绿素荧光诱导动力学曲线分析,研究了盐度降低对热带产胶海藻长心卡帕藻光化学反应的影响,结果表明,盐度降低对PSⅡ反应中心、供体和受体侧的光化学过程产生不同程度的影响。盐度为28时,虽然反应中心开放程度下降11%,受体侧PQ库减小,QA被还原次数下降,反应中心吸收光能出现下降同时热耗散能量出现增加,但是单位面积反应中心RC/CS0,RC/CSm数量显著增加,单位反应中心(或面积)用于电子传递能量都增加,因此最大光能转化效率未降低,光合性能指数甚至增加。上述结果意味着虽然盐度下降到28改变了长心卡帕藻光化学过程,但并没有严重影响到光合作用效率,属于可逆胁变。盐度降低到22时,长心卡帕藻反应中心吸收、捕获和用于电子传递的能量均下降,但是热耗散能上升,反应中心受体侧PQ库和QA被还原次数均显著下降,向反应中心PSⅠ传递的电子受阻,即盐度低于22时长心卡帕藻未有效转化所吸收光能,过剩激发能对光合机构产生损伤,藻体光合开始发生不可逆胁变。当盐度为18时,该藻PSⅡ开放的反应中心数量大大减少,单位面积内电子传递能量也减少,其最大光能转化效率和光合性能指数均明显下降,因此盐度低于18时藻体不可避免地死亡。

The changes of primary photochemical reactions in Kappaphycus alvarezii exposed to low-salinity stress were studied by analyzing their transient chlorophyll a fluorescence dynamic curves.The results show that the main photochemical reaction of PSⅡ,its donor and acceptor sides vary widely in K.alvarezii while being exposed to low-salinity.Although many un-favored profiles like the fraction of PSⅡ centers closed,the storage capacity of plastoquinone（PQ）,the frequency of QA reduced to QA and the absorption energy flux decreased meanwhile the dissipation energy at the level of the antenna chlorophylls increased when K.alvarezii was exposed to salinity of 28,however,the maximal photochemical efficiency of PSⅡ seemed no significantly change and the performance indexes even increased because of number of reversible photochemical regulations such as the increase in the density of reaction center of PSⅡ per excited cross-section of algal sample（RC/CS0 and RC/CSm）,the energy flux of electrons from QA into the electron transport chain per RC（ET0/RC）and the energy flux per CS（ET0/CSm）.While seawater salinity dropped to 22,the storage capacity of PQ and the frequency of QA reduced to QA in K.alvarezii significantly reduced,the electrons transferred to RC of PSⅠ were severely blocked.Therefore,both the light absorbed and trapped as well as the electron transported in K.alvarezii declined,and that the superfluous energy caused a plastic damage to its photosynthetic apparatus.When the salinity further fell to 18,both comprehensive performance indexes and the maximal photochemical efficiency of PSⅡin K.alvarezii distinctly declined due to a rapid decrease in active photosynthetic reaction centers and a heavy interdiction of electron transport flux.Therefore,death of K.alvarezii exposed to such low salinity happened inevitably.