Use of chlorophyll fluorescence in metal-stress research:: a case study with the green microalga Scenedesmus

Metal toxicity on the photosystem 11 (PS 11) photochemistry of the green microalga Scenedesmus obliquus was investigated in vivo using a pulse-amplitude-modulated fluorometer. The results demonstrated that the test metals (copper, chromium, nickel, cadmium, and zinc) inhibited PS II photochemistry substantially, which was clearly evident for F-0, F-v/F-m, qN, and qP following 12 h of metal exposure, whereas F-m, F-v/2, and F-0/F-v depicted significant alteration after only I h of treatment. Thus, metals are not only found to affect the initial and maximal fluorescence, maximum quantum yield, photochemical and nonphotochemical quenching, and plastoquionone pool but the water-splitting apparatus was also significantly altered under metal stress. Among all these fluorescence characteristics, the F-0/F-v registered the highest sensitivity to all the five test metals, thus indicating that the water-splitting apparatus of the oxidizing side of PS II is the primary site of action of toxic metals. This study therefore, concludes that F-0/F-v ratio can be used as a powerful tool in metal-stress research. (C) 2003 Elsevier Science (USA). All rights reserved.