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KMID : 0368419930360030195
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Journal of Plant Biology
1993 Volume.36 No. 3 p.195 ~ p.201
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Comparison of Toxic Effects of Mercury, Copper and Zinc on Photosystem Ⅱ of Barley Chloroplasts
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全鉉植/Chun, Hyun Sik
權寧命/李鎭範/Kwon, Young Myung/Lee, Chin Bum
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Abstract
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The room temperature fluorescence induction of chloroplasts was utilized as a probe to locate the site of inhibition by mercury, copper and zinc on PS Ⅱ by mercury. Inhibitory effect of Hg^2+ on electron transport activity was notable as compared with Cu^2+ and Zn^2+. At concentrations of HgCl_2 over 50 ㎛, activities of PS Ⅱ and whole-chain electron transport decreased more than 70%, while that of PS Ⅰ decreased about 10∼30%. This suggestsa that PS Ⅱ is more susceptible to Hg^2+ than PS Ⅰ is. In the presence of diphenylcarbazide (DPC), 50 ㎛ HgCl_2 inhibited the reduction of dichlorophenolindophenol (DCPIP) about 50%. Addition of heavy metals induced marked decrease in maximal variable fluorescence/initial fluorescene [(Fv)m/Fo], but no changes in Fo. With various concentrations of heavy metals, changes of chlorophyll a fluorescence emitted by PS Ⅱ showed gradual decrease in photochemical quenching (qQ), which indicates an increase in reduced state of electron acceptor, Q_A. Especially, the addition of HgCl_2 caused a notable decrease of qQ. In the presence of 50 ㎛ HgCl_2, energy-dependent quenching (qE) was completely reduced, whereas in the presence of 50 ㎛ CuCl_2 and ZnCl_2 it was still remained. The above results are discussed on the effects of mecury in relation to water-splitting system and plastoquinone (PQ) shuttle system.
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