THESIS
2013
iv leaves, v-xvi, 140 pages : illustrations (some color) ; 30 cm
Abstract
Mercury is notorious for its bioaccumulation in the organisms and biomagnification
along the food web. However, research on the effects of mercury to phytoplankton, at the
bottom of aquatic food chain, is inadequate. Therefore, the present study investigated toxicity,
detoxification, toxicity prediction and pre-exposure effects of inorganic mercury and
methylmercury in marine phytoplankton. We found that: (1) MeHg had no influence on the
electron transport chain, but it inhibited population growth by reducing the rate of algal cells
division. In contrast, Hg(II) could inhibit the electron transport chain, reduce the cell viability
and then population growth. (2) Phytoplankton could synthesize phytochelatins (PCs) to cope
with mercury stress. Both synthesis and degradation/export...[
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Mercury is notorious for its bioaccumulation in the organisms and biomagnification
along the food web. However, research on the effects of mercury to phytoplankton, at the
bottom of aquatic food chain, is inadequate. Therefore, the present study investigated toxicity,
detoxification, toxicity prediction and pre-exposure effects of inorganic mercury and
methylmercury in marine phytoplankton. We found that: (1) MeHg had no influence on the
electron transport chain, but it inhibited population growth by reducing the rate of algal cells
division. In contrast, Hg(II) could inhibit the electron transport chain, reduce the cell viability
and then population growth. (2) Phytoplankton could synthesize phytochelatins (PCs) to cope
with mercury stress. Both synthesis and degradation/export of PCs showed rapid response to
mercury exposure. And the ability of MeHg to induce PCs was much lower than that of
Hg(II). (3) Both subcellular fraction and speciation of mercury could explain and predict the
interspecies differences in mercury sensitivity. For MeHg, the species-related sensitivity
could be interpreted by organelles, metal-rich granule (MRG), or metal sensitive fraction
(MSF) based MeHg. While For Hg(II), heat-stable protein (HSP) or biologically detoxified
metal (BDM) may be the best predictor of the growth inhibition. And the Hg(II) tolerance
also increased with the ability of phytoplankton to biotransform Hg(II) to PCs-Hg complex
and metacinnabar (β-HgS). (4) A unchanged tolerance to Hg(II) while an enhanced tolerance
to MeHg were observed in the multi-generation exposed algal cells, which may be resulted
from the changes in cellular mercury accumulation and their detoxification ability. Overall,
our studies demonstrated the toxicity and detoxification mechanisms of Hg(II) and MeHg in
marine phytoplankton, which are significant in understanding the changes in mercury trophic
transfer and community composition.
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