低温胁迫对玉米幼苗叶绿素荧光诱导动力学的影响

Effects of low temperature on chlorophyll fluorescence kinetics of maize seedlings

为了探讨低温胁迫对玉米幼苗叶片光化学反应的影响机制,本研究基于叶绿素荧光动力学原理,对常温(25℃)和低温处理(2℃)的玉米幼苗叶片进行测量,分别获得快速叶绿素荧光诱导动力学曲线(OJIP曲线)和荧光参数,并应用JIP-test法进行比较分析。结果表明:相比于常温处理,低温胁迫下玉米叶片最大荧光(Fm)和光系统Ⅱ(PSⅡ)潜在光化学效率(FV/FO)分别减少55.3%和65.9%,而初始荧光(FO)基本没有变化;对O-P相的荧光参数进行标准化的WOJ和WJI增大,但WIP减小;J和I相的相对可变荧光Vj和Vi表现相反,Vj增加19.7%而Vi减少16.4%;反映PSⅡ供体侧活性的FK占振幅FO-FJ的比例WK增加44.7%,放氧复合体的组分OEC减少13.1%;反映PSⅡ受体侧电子传递活性的参数Sm、MO、N分别增加210%、49.6%、294%;表示量子产额或能量分配的φPo、ψO、φEO分别减少24.9%、6.82%、29.7%,φDO增加141%;反映单位反应中心活性的参数ABS/RC、TRO/RC、ETO/RC、DIO/RC分别增加70.4%、24.7%、16.1%、328%,而单位面积有活性反应中心密度RC/CSO减少37.4%;表示光合性能的参数PIABS、PICSm分别减少81.6%、90.6%。综合分析玉米叶片光合过程对低温胁迫敏感,其表现的低温逆境防御保护机制是:PSⅡ供体侧的放氧复合体损伤,导致PSⅡ供体侧提供电子的能力下降,反应中心失活数量上升,而单个反应中心的效率增强,多余能量以热量形式散失,减少活性氧(ROS)的产生;低温胁迫造成的玉米叶片PSⅡ供体侧损伤,将抑制电子的传递,进而影响光合能力。

To study the photochemical mechanism of leaves in maize seedlings responded to low temperature stress,the leaf chlorophyll fluorescence was examined under ambient temperature(25℃)and low temperature(2℃)based on chlorophyll fluorescence kinetics.Then,the rapid fluorescence transient(OJIP curve)was obtained,and analyzed with JIP-test.The maximal fluorescence intensity(Fm)and potential photochemical efficiency of photosystemⅡ(PSⅡ)(FV/FO)decreased significantly by 55.3%and 65.9%under low temperature as compared to ambient temperature.With normalized fluorescence transients,WOJ and WJI increased under low temperature,but WIP decreased.The relative variable fluorescence intensity at the J-step and I-step(Vj and Vi)exhibited an opposite trend under low temperature,i.e.Vj increased by 19.7%while Vi decreased by 16.4%.Relative variable fluorescence at 300μs of the chlorophyll fluorescence transient(WK)representing activities of the donor side increased by 44.7%under low temperature.Simultaneously,the fraction of oxygen-evolving complexes(OEC)decreased by 13.1%.The normalized total complementary area above the OJIP transient(Sm),approximated initial slope of the fluorescence transient(MO)and frequency of QA reduction(N)which reflect the change of electron transport activities of the acceptor side increased by 210%,49.7%,294%.Maximum quantum yield for PSⅡprimary photochemistry(φPo),probability that a trapped exciton moves an electron into the electron transport chain beyond QA-(ψO)and quantum yield for PSⅡelectron transport(φEO),decreased by 24.9%,6.82%,29.7%under low temperature.But quantum yield for dissipation(φDO)increased significantly by 141%.The above parameters represent quantum efficiency or flux ratios.Absorption flux per reaction center(RC)(ABS/RC),electron transport flux per RC(ETO/RC),trapped energy flux per RC(TRO/RC)and dissipated energy flux per RC(DIO/RC)increased significantly by 70.4%,24.7%,16.1%and 328%under low temperature,while the density of RCs(RC/CSO)decreased by 37.4%.Two performance indexes on an absorption basis(PIabs,PICSm)decreased by 81.6%and 90.6%under low temperature.Collectively,these results indicate that photosynthesis is a sensitive biological process in maize seedlings under low temperature.The protective mechanism underlying response of photosynthesis under low temperature stress is that the damaged oxygen-evolving complex due to low temperature leads to the decline in the electron-supplying capacity.Moreover,the inactivation of RC is severe,but the efficiency of single RC is enhanced.The redundant energy is consumed as heat coupled with the reduction of reactive oxygen species(ROS).Moreover,the donor side damage of PSⅡdue to low temperature stress results in the blocking of electron transport,thereby influencing photosynthesis capacity.