The Pb-hyperaccumulator aquatic fern Salvinia minima Baker, responds to Pb(2+) by increasing phytochelatins via changes in SmPCS expression and in phytochelatin synthase activity.
The relationship between accumulation of Pb(2+) and the activation of chelation and metal sequestration mechanisms mediated by phytochelatins (PC) was analyzed in the Pb(2+) hyperaccumulator aquatic fern Salvinia minima, after exposure to 40microM Pb(NO(3))(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 Pb(2+) 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 PC(4) was observed in both tissues of exposed S. minima plants relative to unexposed ones, although a higher concentration of PC(4) was found in roots than in leaves. PCS activity and Pb(2+) accumulation was also higher in roots than in leaves. The expression levels of the S. minima PCS gene (SmPCS), in response to Pb(2+) treatment, were also evaluated. In S. minima leaves, the accumulation of Pb(2+) 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 Pb(2+) 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 Pb(2+) accumulation, and phytochelatins do participate as one of the mechanism to cope with Pb(2+) of this Pb-hyperaccumulator aquatic fern.
Estrella-Gómez
N
N
Centro de Investigación Científica de Yucatán Mérida, Mexico.
Mendoza-Cózatl
D
D
Moreno-Sánchez
R
R
González-Mendoza
D
D
Zapata-Pérez
O
O
Martínez-Hernández
A
A
Santamaría
J M
JM
D019881:Aminoacyltransferases / Q000235:genetics / Q000378:metabolism*; D029624:Ferns / Q000187:drug effects* / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D005618:Fresh Water; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects*; D007854:Lead / Q000633:toxicity*; D054811:Phytochelatins / Q000378:metabolism*; D018515:Plant Leaves / Q000201:enzymology / Q000378:metabolism; D018517:Plant Roots / Q000201:enzymology / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D013438:Sulfhydryl Compounds / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000633:toxicity*
D012333:RNA, Messenger; D013438:Sulfhydryl Compounds; D014874:Water Pollutants, Chemical; D007854:Lead; D054811:Phytochelatins; D019881:Aminoacyltransferases; C093784:glutathione gamma-glutamylcysteinyltransferase