chlorophyll-a and Heavy-Metal-Poisoning

Acclimation to heavy metal-induced stress is a complex phenomenon. Among the mechanisms of heavy metal toxicity, an important one is the ability to induce oxidative stress, so that the antioxidant response is crucial for providing tolerance to heavy metal ions. The effect of chronic stress induced by ions of five heavy metals, Ag, Cu, Cr (redox-active metals) Cd, Hg (nonredox-active metals) on the green microalga Chlamydomonas reinhardtii was examined at two levels - the biochemical (content of photosynthetic pigments and prenyllipid antioxidants, lipid peroxidation) and the physiological (growth rate, photosynthesis and respiration rates, induction of nonphotochemical quenching of chlorophyll fluorescence). The expression of the genes which encode the enzymes participating in the detoxification of reactive oxygen species (APX1, CAT1, FSD1, MSD1) was measured. The other gene measured was one required for plastoquinone and α-tocopherol biosynthesis (VTE3). The application of heavy metal ions partly inhibited growth and biosynthesis of chlorophyll. The growth inhibition was accompanied by enhanced lipid peroxidation. An increase in the content of prenyllipid antioxidants was observed in cultures exposed to Cr2O7(2-), Cd(2+) (α- and γ-tocopherol and plastoquinone) and Cu(2+) (only tocopherols). The induction of nonphotochemical quenching was enhanced in cultures exposed to Cu(2+), Cr2O7(2-) and Cd(2+), as compared to the control. Chronic heavy metal-induced stress led to changes in gene expression dependent on the type and concentration of heavy metal ions. The up-regulation of antioxidant enzymes was usually accompanied by the up-regulation of the VTE3 gene.

Topics: Adaptation, Physiological; Antioxidants; Chlamydomonas reinhardtii; Chlorophyll; Environmental Pollutants; Gene Expression Regulation; Heavy Metal Poisoning; Ions; Lipid Peroxidation; Lipid Peroxides; Metals, Heavy; Oxidative Stress; Photosynthesis; Poisoning; Reactive Oxygen Species; Real-Time Polymerase Chain Reaction; Respiration; Up-Regulation

Copper (Cu) is an essential micronutrient for algal growth and development; however, it is also generally considered to be one of the most toxic metals when present at higher levels. Seaweeds are often exposed to low concentrations of metals, including Cu, for long time periods. In cases of ocean outfall, they may even be abruptly exposed to high levels of metals. The physiological processes that are active under Cu stress are largely unknown. In this study, the brown macroalga Sargassum fusiforme was cultured in fresh seawater at final Cu concentrations of 0, 4, 8, 24 and 47 μM. The Cu(2+) concentration and chlorophyll autofluorescence were measured to establish the toxic effects of Cu on this economically important seaweed. The accumulation of Cu by S. fusiforme was also dependent upon the external Cu concentration. Algal growth displayed a general decline with increasing media Cu concentrations, indicating that S. fusiforme was able to tolerate Cu stress at low concentrations, while it was negatively impacted at high concentrations. The term "acute stress" was employed to indicate exposure to high Cu concentrations for 1 day in this study. On the other hand, "chronic stress" was defined as exposure to lower sub-lethal Cu concentrations for 7 days. Proteins were extracted from control and Cu-treated S. fusiforme samples and separated by two-dimensional gel electrophoresis. Distinct patterns of protein expression in the acute and chronic stress conditions were observed. Proteins related to energy metabolism and photosynthesis were reduced significantly, whereas those related to carbohydrate metabolism, protein destination, RNA degradation and signaling regulation were induced in S. fusiforme in response to acute copper stress. Energy metabolism-related proteins were significantly induced by chronic Cu stress. Proteins from other functional groups, such as those related to membranes and transport, were present in minor quantities. These results suggest that S. fusiforme is sensitive to excess Cu, regardless of the presence of acute or chronic stress. We discuss the possible function of these identified proteins, taking into consideration the information available from other plant models.

Topics: Chlorophyll; Copper; Electrophoresis, Gel, Two-Dimensional; Energy Metabolism; Environmental Monitoring; Heavy Metal Poisoning; Metals, Heavy; Photosynthesis; Poisoning; Proteome; Proteomics; Sargassum; Seawater; Seaweed; Water Pollutants, Chemical