Induction of Lead‐Binding Phytochelatins in Vetiver Grass [Vetiveria zizanioides (L.)]

Abstract

Elevated lead (Pb) concentrations in residential houseyards around house walls painted with Pb-based pigments pose serious human health risks, especially to children. Vetiver grass (Vetiveria zizanioides L.) has shown promise for use in in situ Pb phytoremediation efforts. However, little is known about the biochemical mechanisms responsible for the observed high Pb tolerance by vetiver. We hypothesized that vetiver exposure to Pb induced the synthesis of phytochelatins (PC(n)) and the formation of Pb-PC(n) complexes, alleviating the phytotoxic effects of free Pb ions. Our main objective was to identify PC(n) and Pb-PC(n) complexes in root and shoot compartments of vetiver grass using high-performance liquid chromatography coupled to electrospray mass spectrometry (HPLC-ES-MS). After 7 d of exposure to Pb, vetiver accumulated up to 3000 mg Pb kg(-1) in shoot tissues, but much higher Pb concentrations were measured in root ( approximately 20,000 mg kg(-1)), without phytotoxic symptoms. Scanning electron micrographs showed Pb deposition in the vascular tissues of root and shoot, suggesting Pb translocation to shoot. Collision-induced dissociation analyses in MS/ MS mode during HPLC-ES-MS analysis allowed for the confirmation of four unique PC(n) (n = 1-4) based on their respective amino acid sequence. The high tolerance of vetiver grass to Pb was attributed to the formation of PC(n) and Pb-PC(n) complexes within the plant tissues, using ES-MS and Pb mass isotopic patterns. These data illustrate the mechanism of high Pb tolerance by vetiver grass, suggesting its potential usefulness for the remediation of Pb-contaminated residential sites.

Potential of sunflower, castor bean, common buckwheat and vetiver as lead phytoaccumulators

“…Romeiro et al (2006) observed that castor bean plants cultivated under Pb concentrations from 0 and 400 μmol L -1 , in nutrient solution, accumulated ≈ 25,000 g kg -1 of Pb in root dry matter. In vetiver, great capacity of Pb accumulation in the roots and low translocation of this element to the shoots were shown by other authors (Alves et al, 2008;Andra et al, 2009;Danh et al, 2011), highlighting its great potential for Pb phytostabilization. A.…”

“…Such tolerance of vetiver to Pb is probably due to the more efficient mechanisms of defense and detoxification existing in this species (Andra et al, 2009). The compartmentalization in subcellular structures, the decrease in transport through the membrane and formation of chelating peptides rich in proteins, such as phytochelatins, are some of these mechanisms that help, directly or indirectly, plants tolerate the accumulation of Pb and other heavy metals (Yadav, 2010;Hossain et al, 2012;Gupta et al, 2013).…”

Phytoremediation of Explosive-Contaminated Soils

“…This species of grass has a large biomass with the potential for growing larger than 2 m in height and contains a dense root system with the potential for reaching below 3 m underground [28]. Vetiver is a known hyperaccumulator of lead and has the potential for remediating a variety of other heavy metals as well [29,30]. It is also reported to have a high affinity for organic contaminants such as polycyclic aromatic hydrocarbons and explosive compounds [23,31].…”

Utilización de Sustancias Húmicas Comerciales para Optimizar la Fitorremediación de Suelos Mineros Usando Vetiveria (Chrysopogon zizanioides L. Roberty) y Verdolaga (Atriplex portulacoides L.)

“…De acuerdo con Andra et al (2009) esta especie es muy tolerante a la exposición de altas concentraciones de Pb debido a su complejación con fitoquelatinas, por lo que el Zn o el As debieron de ser los causantes principales de la fitotoxicidad. Datta et al (2011) demostraron que la vetiveria es capaz de tolerar niveles moderados de As en el suelo de hasta 225 mg kg -1 , concentración inferior al de este suelo.…”