Antioxidant Responses of Phenolic Compounds and Immobilization of Copper in Imperata cylindrica, a Plant with Potential Use for Bioremediation of Cu Contaminated Environments

Abstract

This work examined the capability of Imperata cylindrica to respond, tolerate and accumulate Cu when growing at high Cu concentration (300 mg kg−1 of substrate) at different times of exposure (2, 14 and 21 days). The Cu accumulation in plants was examined by atomic absorption spectroscopy (AAS) and Cu localized by Scanning Electron Microscopy-Energy Dispersive X-Ray spectroscopy. Additionally, the phenolic compound identifications and concentrations were determined using liquid chromatography coupled to mass spectrometry. Our results showed that root biomass decreased significantly at high Cu levels, with a greater decrease at 21 days (39.8% less biomass in comparison to control). The root showed 328 mg Cu kg−1 dry weight at 21 days of exposure to Cu, being the tissue that accumulates most of the Cu. Lipid peroxidation was a clear indicator of Cu stress, principally in shoots. The exposure to Cu significantly increased the synthesis of phenolic compounds in shoots of plants exposed 21 days to Cu, where 5-caffeoylquinic acid reached the highest concentrations. Our results support that I. cylindrica is a Cu accumulator plant in root organs with a medium level of accumulation (between 200–600 mg Cu kg−1 biomass), which can tolerate the exposure to high Cu levels by means of increasing the synthesis of phenolic compound in shoots, suggesting a potential use as phytoremediation tool in Cu polluted environments.

Main Molecular Pathways Associated with Copper Tolerance Response in Imperata cylindrica by de novo Transcriptome Assembly

“…This also supports the further homogeneity in the shoot samples irrespective of the Cu treatment ( Figure 2 and Figure 3 ). These results are in agreement with previous report by Vidal et al [ 20 ], where high concentrations of Cu (> 300 mg kg −1 DW) were reported in root organs of I. cylindrica , compared to values about 10-fold lower in shoot tissues. The Cu uptake and accumulation firstly occurs at a great magnitude in the root organs, therefore producing a low rate of translocation to shoots [ 33 , 34 ].…”

“…The Probable copper-transporting ATPase HMA5, in turn, plays a key role in transmembrane Cu transport and is specifically induced by Cu in plants [50]. Moreover, studies in Oryza sativa demonstrated that this gene is involved in the loading of Cu to the xylem in roots and other organs [51], playing a key role in the Cu accumulation in root organs, which agrees with other observations by Vidal et al [20]. The joint up-regulation of these genes demonstrated their importance in the Cu detoxification process in the plant roots, since these transporters take Cu ions from the soil, further distributing among plant organs and finally compartmentalize into subcellular organelles in the cell [52].…”

“…After 6 months of growth, the plants were incorporated to the described treatments. To measure the genetic response associated to Cu tolerance mechanisms in I. cylindrica , the controls and treatments were grown in a greenhouse under the conditions described above for 21 days after the Cu application, based on previous reports by Vidal et al [ 20 ]. After this period, the plants were harvested, separated into shoots and root organs (roots and rhizomes), weighed, and immediately frozen at −80 °C for further RNA extraction.…”

“…Some previous studies have shown the ability of I. cylindrica to exude high levels of low molecular weight organic acids [ 19 ] and accumulate this element in its rhizomes over 300 mg Cu kg −1 of dry weight. Moreover, a recent study through scanning electron microscopy and energy dispersive X-ray spectrometer detector confirmed the preferential Cu accumulation in root organs by I. cylindrica [ 20 ].…”

Effect of Lead and Copper on Photosynthetic Apparatus in Citrus (Citrus aurantium L.) Plants. The Role of Antioxidants in Oxidative Damage as a Response to Heavy Metal Stress

“…Our data suggest that these strategies are involved with protection against oxidative damage, thus protection of the photosynthetic machinery. Previous investigations [ 55 ] have also confirmed that plants that produce high amounts of phenolic compounds as a response to the heavy metal stress could be good candidates for phytoremediation.…”