Evidence of sulfur-bound reduced copper in bamboo exposed to high silicon and copper concentrations

abstract We examined copper (Cu) absorption, distribution and toxicity and the role of a silicon (Si) supple-mentation in the bamboo Phyllostachys fastuosa. Bamboos were maintained in hydroponics for 4 monthsand submitted to two different Cu (1.5 and 100 m mCu 2þ ) and Si (0 and 1.1 mM) concentrations. Cu and Sipartitioning and Cu speciation were investigated by chemical analysis, microscopic and spectroscopictechniques. Copper was present as Cu(I) and Cu(II) depending on plant parts. Bamboo mainlycoped withhigh Cu exposure by: (i) high Cu sequestration in the root (ii) Cu(II) binding to amino and carboxyl li-gands in roots, and (iii) Cu(I) complexation with both organic and inorganic sulfur ligands in stems andleaves. Silicon supplementation decreased the visible damage induced by high Cu exposure and modifiedCu speciation in the leaves where a higher proportion of Cu was present as inorganic Cu(I)S compounds,which may be less toxic. 2013 Elsevier Ltd. All rights reserved. 1. IntroductionPhytoremediation technologies are currently used for waste-water treatment (McCutcheon and Schnoor, 2003; Schroder et al.,2007; Vymazal, 2011). Bamboos are known for their high growthrate and biomass production as well as their resistance to a widerange of stress factors (Kleinhenz and Midmore, 2001), and theyare well adapted for the wastewater remediation (Arfi et al., 2009).Wastewater from food and farming industries (such as winery(Arfi et al., 2009), animal breeding (Nicholson et al.,1999)) or fromother industries (such as printing) can be contaminated bydifferent metals, including copper (Cu), a micro-nutrient that canbe toxic at high concentrations and affect the remediationefficiency. Little is known about the absorption and tolerance ofmetal by bamboos (Collin et al., 2013, 2012). In an hydroponicexperiment bamboos, (Gigantocloa sp. “Malay dwarf”) were shownto tolerate a high Cu concentration (Collin et al., 2013) which isknown to be toxic for other Poaceae plants such as wheat (Bravinet al., 2010) and Sabi grass (Kopittke et al., 2009). Therefore, inorder to improve phytoremediation technology, it is essential totest the extent of Cu tolerance in bamboos and identify mecha-nisms by which bamboos are able to cope with an excess Cucontent.Bamboos have been found to be very efficient in accumulatinghighamountsofsilicon(Si)intheirtissues,bothinnatural,i.e.upto183 mg g