The effects of cadmium ions (Cd2+) on the Chl a fluorescence of Ricciocarpos natans were investigated in order to
determine whether Chl fluorescence can be used as a biomarker to estimate the physiological responses of plants to cadmium stress. In all plants treated with Cd2+, the image of Fv/Fm, which represents the maximum photochemical efficiency of PSⅡ,changed as the Cd2+ concentration increased, when treated for 48 h or more. Changes of ΦPSⅡ and QP images were recognized even at 10 μM Cd2+. The Chl a O-J-I-P fluorescence transient was also affected even at 10 μM Cd2+. The fluorescence yield decreased considerably in steps J, I and P in plants treated with Cd2+, although a typical polyphasic rise was observed in non-treated plants. The Chl fluorescence parameters, Fm, Fv/Fo, Sm, SFIabs, PIabs and ETo/CS, decreased as the Cd2+concentration increased, while the Mo and Kn parameters increased. Peroxidase activity decreased significantly and catalase activity increased as the Cd2+ concentration increased. Because of its sensitivity to Cd2+ Ricciocarpos natans is useful in experiments investigating the responses of plants to cadmium exposure. Several parameters (Fm, Fv/Fo, Sm, SFIabs, PIabs,ETo/CS, Mo and Kn) can be applied to determine quantitatively the physiological states of plants under cadmium stress.
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