MERCURIC CHLORIDE DAMAGES THE THYLAKOID MEMBRANE STRUCTURE OF CHLOROPLASTS AND ALTERS THE PROFILES OF SOD, CAT AND EST ISOZYMES IN Chlamydomonas reinhardtii

The effect of mercuric chloride on the thylakoid membrane structure and the banding patterns of antioxidant enzymes in Chlamydomonas reinhardtii (C. reinhardtii) were explored. Three strains of C. reinhardtii, CC-124 (wild type), CC-2473 (psbA) and CC-2913 (NL-11) were used. Ours results showed that Hg2+ inhibited cell growth and reduced the chlorophyll content, strain CC-2913 being the most sensitive to Hg2+. The maximum fluorescence emission peak at an excitation wavelength of 278 or 295nm generally declined in response to increasing Hg2+ concentration indicating that Hg2+ seriously damaged the protein structure. The isoenzymic patterns of several antioxidant enzymes, SOD, CAT and EST were assayed, but the isoenzymic patterns differed between strains, indicating that each strain of alga dealt with Hg2+-induced stress differently and that the mechanism involved might be complex. It is also speculated that CAT might play an important protective role during Hg2+-induced stress.