Cd^(2+)胁迫对鸡爪槭PSⅡ叶绿素荧光动力学特性的影响

Influence of cadmium stress on PSⅡ chlorophyll fluorescence characteristics in the leaves of Acer palmatum

为探讨重金属镉(Cd)对鸡爪槭叶片PSⅡ叶绿素荧光动力学特性的影响,通过盆栽试验对鸡爪槭(Acer palmatum)二年生实生苗进行Cd2+胁迫处理,分别在处理后第15 d、30 d、45 d,测定荧光动力学和荧光参数,并进行JIP-测定(JIP-test)分析。结果表明:Cd2+胁迫降低了鸡爪槭叶片的荧光产量,荧光动力学曲线出现K相的升高;随着Cd2+浓度的增加和胁迫时间的延长,初始荧光F o逐渐升高,在200 mg/kg Cd2+处理达到峰值,表示受体侧电子传递的参数M o上升,S m、Ψo、φEo均呈下降趋势;反应中心密度参数RC/ABS在胁迫后期显著降低,表示单位反应中心活性参数ABS/RC、TR o/RC、DI o/RC增加但速度变缓;ET o/RC略升之后下降,表示PSⅡ光合效率的参数F v/F m和PI abs在胁迫后期显著降低。Cd2+胁迫可抑制或破坏PSⅡ反应中心活性来影响鸡爪槭的生长。低浓度Cd2+(≤50mg/kg)下鸡爪槭通过自身调节机制使过剩光能耗散掉,光合电子传递得到恢复,对PSⅡ伤害较小;中高浓度Cd2+(≥200 mg/kg)会导致PSⅡ反应中心吸收和捕获的光能降低,电子传递受阻,表现出光抑制现象;同时能量耗散受阻,过剩激发能导致活性氧的产生,反应中心发生不可逆失活,从而破坏PSⅡ光合功能。

The photosystem II （PSⅡ） activity of Acer palmatum responding to cadmium stress were investigated bychlorophyll a fluorescence test. The chlorophyll fluorescence kinetics and parameters of two-year-old Acer palmatum weredetermined at 15 d, 30 d and 45 d of cadium（Ca2＋ ） treatments. Ca2＋ concentrations were set at 0 mg/ kg, 50 mg/ kg, 100mg/ kg, 200 mg/ kg, and 400 mg/ kg. Under Cd2＋ stress, the fluorescence intensity decreased, and showed increasing val-ues at K phase of chlorophyll fluorescence kinetic curves. With higher Cd2＋ concentration and longer time, the minimal fluo-rescence Fo increased gradually, and reached the highest point at Cd2＋ concentration of 200 mg/ kg. Mo rose slowly and Sm,追o and 渍Eo fell down. The density of reaction center RC /ABS decreased significantly during late stress period. Theparameters of reaction center activity ABS / RC, TRo / RCand DIo / RC increased slowly. ETo / RC was ascending inthe first and then descending. The maximal photochemicalefficiency of PSⅡ, Fv / Fm and a performance index basedon absorption PIabs reduced significantly in late period.The activity of PSⅡreaction center was destroyed or irre- versibly inhibited by Cd2＋ stress. Under low Cd2＋ concentration （臆50 mg/ kg）, Acer palmatum triggered regulatory mecha-nism to dissipate surplus energy and kept photosynthetic electron transporting, causing minor damage to PSⅡactivity. Un-der medium and high Cd2＋ concentrations （逸200 mg/ kg）, absorption flux and trapped energy flux per CS declined sharplyand electron transport was impeded, leading to photoinhibition of photosynthesis. Simultaneously, energy dissipation wasblocked, and excessive energy excited the overproduction of active oxygen species which induced the irreversible reactioncenter damage and PSⅡphotosynthesis decline.