Coping With Metal Toxicity – Cues From Halophytes

Abstract

Being the native flora of saline soil, halophytes are well studied for their salt tolerance and adaptation mechanism at the physiological, biochemical, molecular and metabolomic levels. However, these saline habitats are getting contaminated due to various anthropogenic activities like urban waste, agricultural runoff, mining, industrial waste that are rich in toxic metals and metalloids. These toxic metals impose detrimental effects on growth and development of most plant species. Halophytes by virtue of their tolerance to salinity also show high tolerance to heavy metals which is attributed to the enhanced root to shoot metal translocation and bioavailability. Halophytes rapidly uptake toxic ions from the root and transport them toward aerial parts by using different transporters which are involved in metal tolerance and homeostasis. A number of defense related physiological and biochemical strategies are known to be crucial for metal detoxification in halophytes however; there is paucity of information on the molecular regulators. Understanding of the phenomenon of cross-tolerance of salinity with other abiotic stresses in halophytes could very well boost their potential use in phytoremediation. In this article, we present an overview of heavy metal tolerance in case of halophytes, associated mechanisms and cross-tolerance of salinity with other abiotic stresses.

Hydrogen sulfide, a signaling molecule in plant stress responses

“…This enzyme thus degrades ACC, the immediate ethylene precursor and is therefore involved in ethylene metabolism in land plants (Mcdonnell et al, 2009). Furthermore, AtDCD2 catalyzes the release of H 2 S from D‐cysteine as well as L‐cysteine (Papenbrock et al, 2007), although this phenomenon has not been observed in rice ( Oryza sativa ; Zhou et al, 2020a). In agreement, rice DCD1 recombinant protein possesses specific D‐CDes activity rather than ACC deaminase activity (Zhou et al, 2020a).…”

Comparative Assessment of Toxic Metals Bioaccumulation and the Mechanisms of Chromium (Cr) Tolerance and Uptake in Calotropis procera

“…A maximum allowable limit of 64 mg/kg Cr is recommended to protect environmental health (Shahid et al, 2017). The use of plants to remove non-essential metals, including Cr, a process termed "phytoremediation, " dates for decades (Nikalje and Suprasanna, 2018). Bioconcentration factor (BCF) and translocation factor (TF) are some of the parameters used in the evaluation of plant metals phytoremediation capacity.…”

Osmoprotectants and Nonenzymatic Antioxidants in Halophytes

“…The strategies exercised by plants characterized as halophytes (Grigore and Toma 2017) that provide efficient osmoprotection and tolerance to salinity and other environmental stresses (e.g., drought, cold, or high temperatures) causing dehydration and cellular turgor loss as well as stress factors like heavy metals and flooding (cross-tolerance, stress memory) were described as more effective in stress response than in glycophytic plants (Mishra and Tanna 2017;Nikalje and Suprasanna 2018;Nikalje et al 2019).…”

“…The resistance/tolerance strategies of halophytes exposed to environmental stresses were widely discussed in many reviews. The aspect of maintenance of cellular osmotic balance and mechanisms of compartmentalization of toxic ions in halophytic plants was summarized by Shabala and Munns (2017) and Nikalje and Suprasanna (2018). The potential of halophytes, growing both in lab/greenhouse conditions and in natural habitats, for the synthesis/accumulation of (i) compatible solutes and/or (ii) antioxidant compounds whose mode of action can be individual or combined, was described by Flowers et al (2015), Slama et al (2015), and Vicente et al (2016).…”