Algae. 1994; 9(2): 237-246.

Characteristics of Fluorescence Induction Kinetics from Ulva pertusa Kjellman and Effects of Mercury

Mee Gyung Kim, Soo Kyung Kang, Choon-Hwan Lee, Chin Bum Lee, Ik Kyo Chung

The Institute of Environmental Research, Inje University. Department of Marine Science, Pusan National University. Department of Molecular Biology, Pusan National University. Department of Biology, Donguei University

The effects of mercury on the photosynthetic machinery of Ulva pertusa Kjellman were examined by measuring oxygen evolution, pigment contents, and fluorescence induction process. By increasing the concentration of added HgCl sub(2) upto 0.6 ppm, oxygen evolution rate and pigment contents were decreased gradually. Chlorophyll a/b ratio was also decreased, suggesting that chlorophyll a was decreased (probably degraded) more rapidly than chlorophyll b by the treatment of mercury. Overall pattern of the fluorescence induction curve was very similar to that measured from terrestrial plant leaves. However, several characteristic differences were observed: (1) fluorescence intensity decreased very rapidly after P(peak), (2) D(dip)-P increase was significantly reduced when measured 30 sec after a saturation pulse, and (3) Fmax was decreased when measured again 30 sec after a first measurement by using a saturation pulse. Due to the second and third characteristics, at least 30 min dark interval was required before starting an additional measurement using a sample. When the mercury concentration was increased, Fp (fluorescence intensity at P) was decreased gradually, but Fi (the intensity at inflection) did not increased. The decrease Fp could be explained by the inhibition of mercury at a site near oxygen evolving complex. By the addition of 0.2 ppm HgCl sub(2), Fp was increased slightly without significant changes in ID pattern. This result suggests that the inhibition site of mercury at the electron transport chain on the reducing side of PSII is not the Q sub(B) or DCMU binding site. When the mercury concentration was increased, Fo was decreased slightly, but Fmax, (Fv)m/Fmax, qQ and qN was decreased significantly. By the addition of mercury more than 0.6 ppm, photosynthetic activities were almost completely blocked but pigment contents was stayed the same.

Keywords : chlorophyll fluorescence, Ulva pertusa, mercury toxicity