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

VANESA L. NEGRIN; ROGÉRIO MENDES; RITA MENDES GODINHO; BÁRBARA TEIXEIRA; 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 accumulate large amounts of metals in their aerial and belowground organs (e.g., Duarte et al., 2010), which implies the existence of mechanisms of tolerance to metal toxicity. Synthesis of thiol-containing molecules is one of the main responses of plants to cope with this (Schant et al., 2002). These molecules consist of monothiols, including cysteine (Cys), γ-glutamylcystein (γ-EC) and glutathione (GSH), and phytochelatins (PCs), which are polymers of glutathione of different length. The sulfhydryl groups of thesemolecules bind metals inactivating them inside the cells. PCs are more efficient in sequestering metal ions than monothiols, and GSH is also a documented defense against oxidative stress (Alscher, 1989).PCs and monothiols are synthetized by several algae and plant species, but to the best of our knowledge, they were never reported for salt marsh species. Here we report the synthesis of these compounds in two Portuguese salt marshes with different level of metal contamination: Rosário, in the Tagus estuary, receives urban effluents from nearby Lisbon and is colonised by Spartina maritima, Halimione portulacoides, Sarcocornia perennis and Salicornia fruticosa, and Óbidos, located in Óbidos lagoon, is vegetated with H. portulacoides and S. perennis. The objective of this work is to document the presence ofthiol-containing molecules in plant parts.MethodologyPlants were sampled in October 2014 at low tide in Rosário (H. portulacoides, S. perennis and S. maritima) and Óbidos (H. portulacoides and 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). Thiol-containing compounds were extracted following the method described in Akhter et al. (2012). Preparation of standards and solutions, derivatization and HPLC conditions were made following Minocha et al (2008). Metal determination was done following Duarte et al. (2010). Reported values are mean ± SD.Results and discussion:Both monothiols and PCs were detected in salt marsh plants. The content of totalmonothiols exceeded or were not significantly different from the concentration of total PCs (see table), as observed by Machado-Estrada et al. (2013) in a mining area. Regarding each monothiol, GSH concentrations were usually an order of magnitude higher than those of γ-EC and Cys. GSH was significantly 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 in the rest of the types of tissues, species and sites. The highest Cys concentration 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 all analyzed plants. PC2 and PC3 were synthesized by all the studied tissues, except PC3 in roots of S.perennis in Óbidos. The concentration of PC2 in large roots of S. maritima (147 ± 55 nmol/g dw) was significantly higher than in the rest of the types of tissues, species and sites. PC4 and PC5 were not detected in roots, except in large roots of S. maritima. PC5, when present, reached concentrations higher than the rest of the PCs. The highest concentration of PC5 (~159 nmol/g dw) wasfound 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 PCs and monothiols it was possible to discern a distribution pattern. High content of PC2 in large roots and PC3 and GSH in leaves of S. maritima is in line with the pioneer ability of this species in contaminated sediments (like in Rosário). In addition, PC4 and PC5 were both found in large roots of S. maritima. The content of PCs in roots of S. maritima is consistent with the values of metals in roots of this species in the area (Duarte et al., 2010). PCA illustrates the specificity of S.maritima.