Pb-hyperaccumulator aquatic fern Salvinia minima Baker, responds to Pb²⁺ by increasing phytochelatins via changes in SmPCS expression and in phytochelatin synthase activity

• Published in: Aquatic toxicology 2009-03, Vol.91 (4), p.320-328
• Main Authors: Estrella-Gómez, N, Mendoza-Cózatl, D, Moreno-Sánchez, R, González-Mendoza, D, Zapata-Pérez, O, Martínez-Hernández, A, Santamaría, J.M
• Format: Article
• Language: English
• Subjects: Animal, plant and microbial ecology; Applied ecology; aquatic plants; bioaccumulation; Biodegradation of pollutants; Biological and medical sciences; biosynthesis; Biotechnology; Ecotoxicology, biological effects of pollution; Effects of pollution and side effects of pesticides on plants and fungi; Environment and pollution; enzyme activity; ferns and fern allies; Fundamental and applied biological sciences. Psychology; gene expression; heavy metals; hyperaccumulators; Industrial applications and implications. Economical aspects; lead; phytochelatins; Salvinia; Salvinia miima; water pollution
• ISSN: 0166-445X; 1879-1514
• DOI: 10.1016/j.aquatox.2008.11.002

The relationship between accumulation of Pb²⁺ and the activation of chelation and metal sequestration mechanisms mediated by phytochelatins (PC) was analyzed in the Pb²⁺ hyperaccumulator aquatic fern Salvinia minima, after exposure to 40μM Pb(NO₃)₂. The tissue accumulation pattern of lead and the phytochelatin biosynthesis responses were analyzed in both, S. minima submerged root-like modified fronds (here named “roots”), and in its aerial leaf-like fronds (“leaves”). S. minima roots accumulated a significantly higher concentrations of Pb⁺² than leaves did. Accumulation of Pb²⁺ in roots was bi-phasic with a first uptake phase reached after 3h exposure and a second higher uptake phase reached after 24h exposure. In leaves, a single delayed, smaller uptake phase was attained only after 9h of exposure. In roots lead accumulation correlated with an increased phytochelatin synthase (PCS) activity and an enhanced PC production. A higher proportion of polymerized PC₄ was observed in both tissues of exposed S. minima plants relative to unexposed ones, although a higher concentration of PC₄ was found in roots than in leaves. PCS activity and Pb²⁺ accumulation was also higher in roots than in leaves. The expression levels of the S. minima PCS gene (SmPCS), in response to Pb²⁺ treatment, were also evaluated. In S. minima leaves, the accumulation of Pb²⁺ correlated with a marked increase in expression of SmPCS, suggesting a transcriptional regulation in the PCS activation and PC accumulation in this S. minima tissue. However, in roots, the basal expression of SmPCS was down-regulated after Pb²⁺ treatment. This fact did not correlate with the later but strong increase in both, PCS activity and PC production; suggesting that the PC biosynthesis activation in S. minima roots occurs only by post-translational activation of PCS. Taken together, our data suggest that the accumulation of PC in S. minima is a direct response to Pb²⁺ accumulation, and phytochelatins do participate as one of the mechanism to cope with Pb²⁺ of this Pb-hyperaccumulator aquatic fern.