桑树叶片光系统Ⅱ对NaCl和Na_2CO_3胁迫的响应

Responses of photosystem Ⅱ in leaves of mulberry to NaCl and Na_2CO_3 stress

为探讨桑树叶片PSⅡ在中性盐NaCl和碱性盐Na2CO3胁迫下的生理响应,采用快相叶绿素荧光技术研究了不同浓度的NaCl和Na2CO3溶液中PSⅡ功能的快速响应。结果表明:NaCl浓度低于100mmol/L时,叶绿素荧光参数没有明显变化;超过100mmol/L时,桑树叶片的QA被完全还原时所需要的能量(Sm)、吸收光能用于QA-以后的电子传递的量子产额(φE0)、单位反应中心捕获的用于还原QA的能量(TR0/RC)和单位反应中心捕获的用于电子传递的能量(ET0/RC)明显降低,而OJIP曲线上J点的相对可变荧光强度(VJ)、QA被还原的最大速率(M0)、非光化学猝灭的最大量子产额(φD0)和单位反应中心耗散掉的能量(DI0/RC)增加;盐胁迫抑制了PSⅡ受体侧QA向QB的电子传递,PSⅡ电子传递链受体侧QB位点和PQ库容量发生了改变,叶片捕获光能的比例降低,热耗散的比例增加,QA-之后的电子传递能量比例减少。当NaCl浓度为200mmol/L时,桑树叶片的PSⅡ最大光化学效率(Fv/Fm)和PSⅡ的潜在光化学活性(Fv/F0)明显降低,叶片发生了光抑制。在相同Na+浓度下,碱性盐(Na2CO3)胁迫是通过较高的pH降低了类囊体膜两侧存在的ΔpH而抑制或伤害桑树叶片PSⅡ,因此,碱性盐对桑树叶片PSⅡ的伤害程度大于中性盐(NaCl)。

The study was conducted to investigate physiological reactions of photosystem Ⅱ in leaves of mulberry to NaCl and Na2CO3 stress using the fast fluorescence transients as technology.The results showed that fluorescence parameters had no difference under low concentration NaCl（100 mmol/L） treatment,but the fluorescence parameters of normalised total complementary area above the OJIP transie（Sm）,quantum yield for electron transport（φE0）,maximal trapped energy flux per reaction center（TR0/RC） and electron transport flux per reaction center（ET0/RC） decreased obviously when NaCl concentration was above 100 mmol/L,while the parameters of relative variable fluorescence intensity at the J-step（VJ）,the reduction of QA maximum rate（M0）,quantum yield for dissipated energy（φD0） and dissipated energy flux per reaction center（DI0/RC） increased.Electron transports in the receptor side of PSⅡfrom QA to QB were impeded under salt stress,the main reason was that the locus of QB and capacity of PQ had been changed,the ratio of capture photons had been decreased,the ratio of heat energy had been increased,the electron had been reduced after QA.The PSⅡphotochemical efficiency（Fv/Fm） and PSⅡ potential activities（Fv/F0） in mulberry leaves under 200 mmol/L NaCl stress had been significantly increased,and photoinhibitation was occurred.Meanwhile,high pH in alkali salt（Na2CO3） decreased pH difference between inner and outside thylakoid membrane at the same Na＋concentration as neutral salt to inhibit or injure PSⅡ.It is concluded that PSⅡin mulberry leaves is damaged heavier under alkali salt stress than that of neutral salt（NaCl）.