Abstract
Hyperaccumulation and hypertolerance of Trace Metal Elements (TME) like Cd and Zn are highly variable in pseudo-metallophytes species. In this study we compared the impact of high Cd or Zn concentration on the photosynthetic apparatus of the Arabidopsis arenosa and Arabidopsis halleri pseudo-metallophytes growing on the same contaminated site in Piekary Slaskie in southern Poland. Plants were grown in hydroponic culture for 6 weeks, and then treated with 1.0 mM Cd or 5.0 mM Zn for 5 days. Chlorophyll a fluorescence and pigment content were measured after 0, 1, 2, 3, 4, and 5 days in plants grown in control and exposed to Cd or Zn treatments. Moreover, the effect of TME excess on the level of oxidative stress and gas-exchange parameters were investigated. In both plant species, exposure to high Cd or Zn induced a decrease in chlorophyll and an increase in anthocyanin contents in leaves compared to the control condition. After 5 days Cd treatment, energy absorbance, trapped energy flux and the percentage of active reaction centers decreased in both species. However, the dissipated energy flux in the leaves of A. arenosa was smaller than in A. halleri. Zn treatment had more toxic effect than Cd on electron transport in A. halleri compared with A. arenosa. A. arenosa plants treated with Zn excess did not react as strongly as in the Cd treatment and a decrease only in electron transport flux and percentage of active reaction centers compared with control was observed. The two species showed contrasting Cd and Zn accumulation. Cd concentration was almost 3-fold higher in A. arenosa leaves than in A. halleri. On the opposite, A. halleri leaves contained 3-fold higher Zn concentration than A. arenosa. In short, our results showed that the two Arabidopsis metallicolous populations are resistant to high Cd or Zn concentration, however, the photosynthetic apparatus responded differently to the toxic effects.
Highlights
Due to industrial and agricultural activities, such as mining, smelting, traffic, using of fertilizers, and sewage sludges, as well as natural processes including atmospheric deposition and weathering of minerals metal contamination has become serious environmental problem worldwide (Alloway, 2013; Su et al, 2014).Cadmium (Cd) is considered as one of the most toxic non-essential elements for plants (Clemens and Ma, 2016)
In order to gain a better understanding of mechanisms underlying metal tolerance of A. halleri and A. arenosa, metal content, photosynthetic activity, levels of oxidative stress, gasexchange parameters, chlorophyll, flavonol, and anthocyanin indices were analyzed in metallicolous populations from the same contaminated site in southern Poland grown in control, and exposed to high Cd and Zn concentrations
It is tempting to suggest that the higher accumulation of Zn by A. halleri and higher accumulation of Cd by A. arenosa is connected with different transport activity of transporters responsible for the uptake and translocation of both metals in plants
Summary
Due to industrial and agricultural activities, such as mining, smelting, traffic, using of fertilizers, and sewage sludges, as well as natural processes including atmospheric deposition and weathering of minerals metal contamination has become serious environmental problem worldwide (Alloway, 2013; Su et al, 2014).Cadmium (Cd) is considered as one of the most toxic non-essential elements for plants (Clemens and Ma, 2016). Arabidopsis halleri and A. arenosa are pseudo-metallophytes closely related to A. thaliana (Clauss and Koch, 2006), which are used to study the adaptation to environments highly contaminated with TME. Both species can be commonly found on metalliferous and non-metalliferous sites in southern Poland (Fiałkiewicz and Rostanski, 2006; Szarek-Łukaszewska and Grodzinska, 2007, 2011; Preite et al, 2018). While Zn hyperaccumulation is a constitutive trait, Cd accumulation is highly variable within A. halleri populations (Pauwels et al, 2012; Meyer et al, 2015; Sitko et al, 2017; Stein et al, 2017; Corso et al, 2018; Frérot et al, 2018; Schvartzman et al, 2018), whereas these traits are poorly studied in A. arenosa
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