The response of the freshwater microalga Chlorella vulgaris to mercuric ion (Hg2+) stress was examined using chlorophyll a fluorescence image analysis and O-J-I-P analysis as a way to monitor the toxic effects of mercury on water ecosystems. The levels of photosynthetic pigments, such as chlorophyll a and b and carotenoids, decreased with increasing Hg2+ concentration. The maximum photochemical efficiency of photosystem Ⅱ(Fv/Fm) changed remarkably with increasing Hg2+ concentration and treatment time. In particular, above 200 μM Hg2+, considerable mercury toxicity was seen within 2 h. The chlorophyll a fluorescence transient O-J-I-P was also remarkably affected by Hg2+; the fluorescence emission decreased considerably in steps J, I, and P with an increase in Hg2+ concentration when treated for 4 h. Subsequently, the JIP-test parameters (Fm, Fv/Fo, RC/CS, TRo/CS, ETo/CS, ΦPO, ΨO and ΦEO) decreased with increasing Hg2+ concentration, while N, Sm, ABS/RC, DIo/RC and DIo/CS increased. Therefore, a useful biomarker for investigating mercury stress in water ecosystems, and the parameters Fm, ΦPO, ΨO, and RC/CS can be used to monitor the environmental stress in water ecosystems quantitatively.

Abstract
 1. 서 론
 2. 재료 및 방법
  2.1. 실험재료 및 배양
  2.2. 엽록소 형광이미지 분석
  2.3. 엽록소 및 carotenoid 함량의 분석
  2.4. 엽록소형광 O-J-I-P 곡선의 분석
  2.5. 통계분석
 3. 결과 및 고찰
  3.1. 엽록소형광 특성의 변화
  3.2. 엽록소 및 carotenoid 함량의 변화
  3.3. 엽록소형광 O-J-I-P 곡선의 변화
  3.4. 광계Ⅱ에서의 에너지 흐름의 변화
 4. 결 론
 참 고 문 헌

• Soonja Oh(Agricultural Research Center for Climate Change, National Institute of Horticultural and Herbal Science, RDA)
• Seok Chan Koh(Department of Biology, Jeju National University) Corresponding author