Many areas intended for crop production suffer from the concomitant occurrence of heavy metal pollution and elevated salinity; therefore, halophytes seem to represent a promising perspective for the bioremediation of contaminated soils. In this study, the influence of Cd treatment (0.01-10.0 mM) and salinity stress (0.4 M NaCl) on the expression of genes involved in heavy metal uptake (irt2-iron-regulated protein 2, zip4-zinc-induced protein 4), vacuolar sequestration (abcc2-ATP-binding cassette 2, cax4-cation exchanger 2 pcs1-phytochelatin synthase 1) and translocation into aerial organs (hma4-heavy metal ATPase 4) were analyzed in a soil-grown semi-halophyte Mesembryanthemum crystallinum. The upregulation of irt2 expression induced by salinity was additionally enhanced by Cd treatment. Such changes were not observed for zip4. Stressor-induced alterations in abcc2, cax4, hma4 and pcs1 expression were most pronounced in the root tissue, and the expression of cax4, hma4 and pcs1 was upregulated in response to salinity and Cd. However, the cumulative effect of both stressors, similar to the one described for irt2, was observed only in the case of pcs1. The importance of salt stress in the irt2 expression regulation mechanism is proposed. To the best of our knowledge, this study is the first to report the combined effect of salinity and heavy metal stress on genes involved in heavy metal trafficking.Plants 2020, 9, 475 2 of 15 by the occurrence of three symptoms: first, increased osmotic pressure, which results in water deficit conditions; second, accumulation of toxic ions in plant organs [4]; and third, nutritional imbalance, which influences the growth and development of challenged plants [5]. These symptoms are primarily responsible for adverse alterations in morphological, physiological and biochemical processes that disrupt the agricultural production and ecological balance of the area [3].Many areas, including arable lands, suffer from concomitant contamination with heavy metals (HMs) and salts. Recently, the accumulation of HMs in the environment has increased as a consequence of intensified human activities, such as mining, smelting and agricultural practices, including the long-term application of fertilizers, fungicides or pesticides [6]. Since HMs are non-degradable, they may persist in a contaminated substrate for decades [7]. The threat posed by heavy metals to humans has an origin in plants, which are the first link in the food chain. Plants can take up HMs from various sources, such as air, water or soil; the latter process predominates and is dependent on many factors, such as temperature, soil pH, aeration and, clearly, on the particular species involved in the accumulation process.Cadmium is one of the HMs that is particularly widely spread in the environment and has gained prominence as an important issue not only in urbanized lands, but also in less explored, rural, agricultural or wildlife areas. Cd toxicity results from altered uptake and transport of nutrient elements (Ca, Mg, P), disruption ...

No abstract

The common ice plant (Mesembryanthemum crystallinum L.) is a widely studied model due to its tolerance to numerous biotic and abiotic stresses. In this study, carried out in model pots, the plants were treated with variant doses of Cd(II) and Cr(VI) and proved resistant to extreme levels of these heavy metals. Initial toxicity symptoms were observed upon final concentrations of 818 mg Cd kg−1 soil d.w., and 1699 mg Cr kg−1 applied as potassium chromate. Biometric analyses revealed that none of the Cr(VI) doses affected dry weight of the plant organs thus maintaining the shoot-to-root ratio. The Cd and Cr hypertolerance strategies were divergent and resulted in different accumulation patterns. For the case of Cd(II), an excluder-like mechanism was developed to prevent the plant from toxicity. For chromate, high accumulation potential together with Cr(VI) root-to-shoot translocation at sublethal concentrations was revealed (up to 6152 mg Cr kg−1 shoot at 4248 mg Cr kg−1 soil). It is concluded that M. crystallinum reveals considerable phytoremediation capabilities due to unique growth potential in contaminated substrates and is suitable for bioreclamation of degraded soils. The plant is especially applicable for efficient phytoextraction of chromate-contamination, whereas for Cd-affected areas it may have a phytostabilizing effect.