Abstract:

The switch from C3 to CAM pathway was induced by water stress in a C3 /CAM intermediate plant Sedum spectabile Boreau. Typical CAM criteria were observed upon 15 d of withholding water. Leaf δ13C value (-‰) and water content showed a linear correlation fashion. Chlorophyll fluorescence parameters and antioxidative capacity were altered by water stress.ΦPSⅡ and qP were reduced by 50% and 34% of the control, respectively, while NPQ rose ca .180%. SOD activity and ability to scavenge DPPH· free radical went down but membrane permeability changed slightly. However, when an additional photooxidation by MV with high PPFD was carried out with leaf discs from watered (C3 mode) and drought plants (CAM mode), qP andΦPSⅡ in leaves at induced CAM mode stage continuously decreased to a very low level. High 1-qP value (0.86) and 1-qP/NPQ ratio (>1)indicated the presence of high reduction state and unbalance of light energy budget. Together with the marked loss of membrane integral, it was evidenced that photooxidative damage was more serious in the induced CAM mode than in the C3 mode. No advantage of photooxidation tolerance was found at the induced CAM expression stage of the facultative CAM plant, as compared with its C3 mode stage, and also with the constitutive CAM plants reported previously. The differences in photooxidation sensitivity between the inducible CAM expressing plant and the constitutive CAM plant were discussed. Key words: Sedum spectabile; facultative CAM plant; photooxidation; water stress; CAM expression

兼性CAM 植物长叶景天叶片在!C3和CAM 型时的光氧化作用
林植芳  彭长连 林桂珠
（中国科学院华南植物研究所，广州510650)

摘要： 通过停止浇水产生水分胁迫使兼性CAM植物长叶景天（Sedum spectabile Boreau)叶片光合途径由C3型转为CAM型。干旱15d时观察到典型的CAM生理特征，且叶片的？13C值与含水量成线性相关。水分胁迫改变了叶绿素荧光参数和抗氧化能力，和Φ_PSⅡ和qp降低34％，NPQ提高约180％，SOD活性和清除DPPH自由基能力也明显下降，但膜半透性变化不大，当将处于C₃（浇水）和诱导为CAM（缺水）型的叶圆片用源甲基紫精（MV）和强光作光氧化处理后，与C₃型叶片相比，诱导CAM型叶片的NPQ不能提高，qp和ΦPSⅡ降至很低水平，光系统处于高还原态，光能供给与消耗失衡（1－qp=0.86和（1－qp)/NPQ>1)，膜系统几乎失去完整性，这种严重的光氧化损伤表明，与我们以前报告的专性CAM植物诱导表达的CAM型未能显示比C₃型较强的耐光氧化优势。讨论了出现这种光氧化敏感性差别的可能原因。 (共6页)