Phytochelatin induction by selenate in Chlorella vulgaris, and regulation of effect by sulfate levels

Abstract

Phytochelatins (PCs) are short metal detoxification peptides made from the sulfur-rich molecule glutathione. The production of PCs by algae caused by Se exposure has never been studied, although many algae accumulate Se, forming Se-rich proteins and peptides, and higher plants have demonstrated PC production when treated with Se; therefore, a goal of the current study was to examine whether Se induces PC production in algae. Furthermore, selenate is thought to compete with sulfate in the S assimilation pathway, and sulfate therefore may have a protective effect against the toxic effects of high doses of Se in algae. Hence, the interaction of selenate and sulfate was investigated with respect to the induction of PCs. Chlorella vulgaris was cultured in media with either low (31.2 µM) or high (312 µM) concentrations of sulfate. These cultures were exposed to selenate in doses of 7, 35, and 70 nM for 48 h. In a separate treatment, Cd (890 nM) was added as a positive PC-inducing control, and one no-metal negative control was used. Total Se and Se speciation were determined, and glutathione, phytochelatin-2, and phytochelatin-3 were quantified in each of cell digests, cell medium, and cell lysates. We found that PCs and their precursor glutathione were induced by selenate as well as by a Cd control. The high concentration of sulfate was able to counter selenate-induced production of PCs and glutathione. These data support two possible mechanisms: a negative feedback system in the S assimilation pathway that affects PC production when sulfate is abundant, and competition for uptake at the ion transport level between selenate and sulfate.

Effect of Selenate on Viability and Selenomethionine Accumulation ofChlorella sorokinianaGrown in Batch Culture

“…Based on PSII fluorescence, oxygen evolution, and pigment production data, it can be concluded that 40 mg·L −1 of selenate was a sublethal concentration for Chlorella sorokiniana culture and can therefore be used for SeMet accumulation studies. Similar findings for Chlorella vulgaris were reported in which chlorophyll production was not significantly affected by exposure to selenate during 9 days of batch cultivation [9]. …”

“…The primary cause of Se deficiency that reduces growth, reproduction, and even causes death is its low amount in soil and consequently in animal feed [8]. Selenium bioeffects are mainly involved in immune function, reproduction, metal toxicity resistance, and other biological functions [9]. Besides, selenium has been proven to be an effective anticancer agent mainly based on statistical and model studies [10], when it is supplied in a suitable bioactive form [11–13].…”

Melatonin mediates selenium‐induced tolerance to cadmium stress in tomato plants

“…15,67 Se could activate PCs synthase, increase the amount of PC precursors, and stimulate plants to produce more PCs that would eventually form more heavy metal-PC complexes. 68 Our recent study found that melatonin increased the GSH content by stimulating the activity of γ-glutamylcysteine 69 and elevated the PC content by activating PC biosynthetic genes, PCS 15 . In agreement with earlier results, we found that Se, Cd, and melatonin increased the levels of GSH and PCs in tomato leaves (Fig.…”

Assessing Different Mechanisms of Toxicity in Mountaintop Removal/Valley Fill Coal Mining-Affected Watershed Samples Using Caenorhabditis elegans

“…We found that pcs-1 ( tm1748 ) knockouts were more sensitive than wild-type to selenium, which is a known contaminant of the Mud River. While the relationship between phytochelatin and selenium remains unstudied in nematodes, algae [52] produce phytochelatin upon exposure to selenium, and selenium forms trisulfide linkages with phytochelatin in vitro [38]. The greater sensitivity of pcs-1 ( tm1748 ) knockout nematodes to sodium selenite in comparison to wild-type worms and a corresponding lack of induction of metallothionein expression after exposure to selenium, in concert with research by other groups demonstrating the greater importance of phytochelatin in comparison to metallothionein in the elimination of metals, suggest that phytochelatin is responsible for mitigating the effects of excess selenium in nematodes.…”