Complexation and Toxicity of Copper in Higher Plants. I. Characterization of Copper Accumulation, Speciation, and Toxicity inCrassula helmsiias a New Copper Accumulator    

Abstract

The amphibious water plant Crassula helmsii is an invasive copper (Cu)-tolerant neophyte in Europe. It now turned out to accumulate Cu up to more than 9,000 ppm in its shoots at 10 mM (=0.6 ppm) Cu 2+ in the nutrient solution, indicating that it is a Cu hyperaccumulator. We investigated uptake, binding environment, and toxicity of Cu in this plant under emerged and submerged conditions. Extended x-ray absorption fine structure measurements on frozen-hydrated samples revealed that Cu was bound almost exclusively by oxygen ligands, likely organic acids, and not any sulfur ligands. Despite significant differences in photosynthesis biochemistry and biophysics between emerged and submerged plants, no differences in Cu ligands were found. While measurements of tissue pH confirmed the diurnal acid cycle typical for Crassulacean acid metabolism, D 13 C measurements showed values typical for regular C3 photosynthesis. Cu-induced inhibition of photosynthesis mainly affected the photosystem II (PSII) reaction center, but with some unusual features. Most obviously, the degree of light saturation of electron transport increased during Cu stress, while maximal dark-adapted PSII quantum yield did not change and light-adapted quantum yield of PSII photochemistry decreased particularly in the first 50 s after onset of actinic irradiance. This combination of changes, which were strongest in submerged cultures, shows a decreasing number of functional reaction centers relative to the antenna in a system with high antenna connectivity. Nonphotochemical quenching, in contrast, was modified by Cu mainly in emerged cultures. Pigment concentrations in stressed plants strongly decreased, but no changes in their ratios occurred, indicating that cells either survived intact or died and bleached quickly.

In Situ Distribution and Speciation of Toxic Copper, Nickel, and Zinc in Hydrated Roots of Cowpea

“…For example, in the roots, stems, and leaves of E. splendens (a Cutolerant plant) grown in 300 mM Cu for 10 to 60 d, most Cu was bound to O-containing ligands in the cell wall (Shi et al, 2008). Similarly, Kü pper et al (2009) reported that, in frozen, hydrated shoots of Crassula helmsii grown for 8 d at 10 mM Cu, Cu was bound by O ligands (such as organic acids). However, other studies have reported Cu to be bound to S-containing ligands.…”

“…Finally, although metals are known to induce toxicities within minutes or hours of exposure (Blamey et al, 2004, most studies determine metal speciation after comparatively long periods of exposure (often days or weeks). For example, although Mijovilovich et al (2009), van Steveninck et al (1994, and Kü pper et al (2009) utilized frozen, hydrated samples grown at relevant concentrations, the plants were exposed to metals for comparatively long periods of time (7 d to 4 months). While these studies provide useful data about long-term toxicity, the speciation after these extended periods may not be related to the initial toxic effects of the metals (or the initial response of the plants to metal toxicity).…”

Influence of Soil Chemistry and Plant Physiology in the Phytoremediation of Cu, Mn, and Zn

“…Furthermore, Eleocharis acicularis can accumulate a maximum of 20200 μg g −1 of Cu in its shoots, suggesting great potential for use in the phytoremediation of water environments (Sakakibara et al, 2011). The amphibious water plant Crassula helmsii can also hyperaccumulate Cu (Kupper et al, 2009). Based on the Cu accumulation of Azolla filiculoides (6013 μg g −1 ), this species can be regarded as a potential phytoremediation organism with high potential for cleaning water polluted with Cu (Valderrama et al, 2012).…”

Bioaccumulation and changes in the photosynthetic apparatus of Prosopis juliflora exposed to copper

“…In this sense, chlorophyll a flourescence represent an excellent screening tool for evaluation of heavy metal stress in aerial parts of plants (Kummerová et al, 2010;Hussain et al, 2011 is replaced by Cu +2 from the water-splitting apparatus at the oxidizing side, resulting in a disruption of photosynthetic reactions (Küpper et al, 2009). Additionally, the decline in the F v /F 0 ratio is indicative of a decline in the rate of photochemistry as the primary electron acceptor pool (Q n ) became increasingly oxidized, or a reduction of the pool size of the primary electron acceptors associated with PSII activity (Krause and Weiss, 1991).…”