【摘要】 高浓度Ca²⁺（0.1 mol/L）使叶绿体产生O₂⁺的能力下降,旋转相关时间（τ_c）增大34.3％,即膜的流动性降低,并抑制ACC形成乙烯;衰老时细胞内的Ca²⁺作用却与此相反;O₂⁺的生成与乙烯的产量成正相关（r=0.941）。EGTA,吩噻嗪和W₇等加入到叶绿体反应体系中,可使O₂⁺的产量下降,ACC形成乙烯减少;相反,亚油酸作为Ca²⁺载体,却使之明显升高,但亚油酸本身产生乙烯的量比ACC少得多。因此推测:高浓度Ca²⁺可能影响叶绿体膜的状态,从而影响EFE的构象或者减少O₂⁺的生成,抑制ACC的转化,衰老时细胞内的Ca²⁺可启动钙信使系统,使O₂⁺的产量升高,而其中膜脂过氧化是衰老的中心环节,因此O₂⁺的升高可能是诱发衰老启动的重要因素。更多还原

【Abstract】 The effects of calcium in the propensity to generate superoxide radical and to form ethylene from ACC were investigated with electron-paramagnetic-resonance spectroscopy.（1）. The rate of ethylene formation from ACC, superoxide radical production and membrane fluidity were decreased by treatment with exogenous Ca²⁺ (10^-1 mol /L), but during senescence the opposite effects were observed by endogenous Ca²⁺ of chloroplasts, isolated from wheat seedlings irrigated with Ca²⁺ (10^-1 mol/L).（2）. The effects of endogenous Ca²⁺ concentration in increasing O_<sup>- and ethylene production were inhibited by CaM antagonists, such as phenothiazine （50 μmol / L） and W₇ （50 μmol / L）, and promoted by exogenous linoleic acid, which was considered an endogenous Ca²⁺ ionophore. Linoleic acid was probably the precursor of ethylene, but much less ethylene was produced from it than from ACC. O₂^- levels was positively correlated to ethylene production regulated by endogenous Ca²⁺（r=0.941）.These results implied that exogenous Ca²⁺ may affect membrane state, and hence change the configuration of ethylene forming enzyme or decrease O₂^- production and inhibit the conversion of ACC to ethylene. These also suggested that during senescence internalized Ca²⁺ may induce the increase of superoxide radical production, and then enhance the ethylene formation from its precursor. According to above findings, lipid peroxidation caused by O₂^- and other activated oxygen play a key role in triggering senescence in chloroplasts.更多还原