First evidence of metal tolerance involving phytochelatins and monothiols in salt marsh plants

VANESA L. NEGRIN; BÁRBARA TEIXEIRA; RITA MENDES GODINHO; ROGÉRIO MENDES; CARLOS VALE

Santa Fe

Conferencia; III Conferencia Panamericana de Sistemas de Humedales para el Tratamiento y Mejoramiento de la Calidad del Agua; 2016

Facultad de Ing. Química- Universidad Nacional del Litoral

IntroductionMost salt marsh plants accumulatelarge amounts of metals in their aerial and belowground organs (e.g., Duarte etal., 2010), which implies the existence of mechanisms of tolerance to metaltoxicity. Synthesis of thiol-containing molecules is one of the main responsesof plants to cope with this (Schant et al., 2002). These molecules consist ofmonothiols, including cysteine (Cys), γ-glutamylcystein (γ-EC) andglutathione (GSH), and phytochelatins (PCs), which are polymers of glutathioneof different length. The sulfhydryl groups of these molecules bind metalsinactivating them inside the cells. PCs are more efficient in sequesteringmetal ions than monothiols, and GSH is also a documented defense againstoxidative stress (Alscher, 1989).PCsand monothiols are synthetized by several algae and plant species, but to thebest of our knowledge, they were never reported for salt marsh species. Here wereport the synthesis of these compounds in two Portuguese salt marshes with differentlevel of metal contamination: Rosário, in the Tagus estuary, receives urbaneffluents from nearby Lisbonand is colonised by Spartina maritima,Halimione portulacoides, Sarcocornia perennis and Salicornia fruticosa, and Óbidos, located in Óbidos lagoon, isvegetated with H. portulacoides and S. perennis. The objective of this workis to document the presence of thiol-containing molecules in plant partsMethodologyPlantswere sampled in October 2014 at low tide in Rosário (H. portulacoides, S.perennis and S.maritima) and Óbidos(H. portulacoidesand S.perennis) marshes. Each plant was separated in above and belowground parts, which were washed separately. S. maritima roots were separated in two sizes, small (<1mm) and largeroots (> 1mm). Thiol-containing compounds wereextracted following the method described in Akhter et al. (2012). Preparationof standards and solutions, derivatization and HPLC conditions were madefollowing Minocha et al (2008). Metal determination was done following Duarte et al. (2010). Reportedvalues are mean ± SD.Resultsand discussion:Both monothiols and PCs were detected in salt marshplants. The content oftotal monothiols exceeded or were not significantly different from theconcentration of total PCs (see table), as observed by Machado-Estrada et al. (2013)in a mining area. Regarding each monothiol, GSH concentrationswere usually an order of magnitude higher than those ofγ-EC and Cys. GSH wassignificantly higher in aboveground tissues than in roots for all species,which might be related with higher environmental stress in aerial parts(Alscher, 1989).Values of GSH were significantly higher in leaves of S.maritima (1886 ± 236 nmol/g) than inthe rest of the types of tissues, species and sites. The highest Cysconcentration was also found in S.maritima, in large roots. γ-EC was produced only by above and belowground tissues of S.maritima and H.portulacoides from Rosário, being the concentration in S.maritima significantly higher. Production of PCs occurred in roots and in above parts of allanalyzed plants. PC2 and PC3 were synthesized by all thestudied tissues, except PC3 in roots of S.perennis in Óbidos. The concentration of PC2 in largeroots of S. maritima (147 ± 55 nmol/gdw) was significantly higher than in the rest of the types of tissues, speciesand sites. PC4 and PC5 were not detected in roots, exceptin large roots of S. maritima. PC5,when present, reached concentrations higher than the rest of the PCs. Thehighest concentration of PC5 (~159 nmol/g dw) was found in stems of S.perennis in either salt marsh,followed by small roots of S. maritima.In spite of the variability in the production of the different PCsand monothiols it was possible to discern a distribution pattern. High contentof PC2 in large roots and PC3 and GSH in leaves of S. maritima is in line with the pioneerability of this species in contaminated sediments (like in Rosário). Inaddition, PC4 and PC5 were both found in large roots of S. maritima. The content of PCs in rootsof S. maritima is consistent with the values of metals in roots ofthis species in the area (Duarte et al., 2010). PCA illustrates thespecificity of S. maritima.