Heavy metal tolerance in two Algerian saltbushes: A review on plant responses to cadmium and role of calcium in its mitigation

Abstract

Heavy metal pollution is a common environmental constraint to human health. The physicochemical decontamination constitutes a high costly procedure and not practicable in extensive polluted soils. Therefore, selecting plants naturally tolerant to heavy metals is an alternative approach for a sustainable phytoremediation. The aptitude of species to tolerate heavy metals is determined by several biochemical trails that protect photosynthetic apparatus and maintain growth and chemical elements homeostasis. Cadmium (Cd) is a high toxic environmental pollutant and can interfere with various metabolic processes such as photosynthesis, respiration, and mineral uptake and some enzymatic activities that are crucial for plant growth. Atriplex halimus L. and A. nummularia L. (Amaranthaceae) are two widespread saltbushes used for desalination and rehabilitation of Algerian saline lands. These shrubs have a high biomass production, extensive root system, low nutrient requirements, and easy propagation, among other benefits. Calcium (Ca) supplementation was largely used to improve heavy metal tolerance of plant species. Ca is an indispensable element for plant growth, membrane integrity, osmotic adjustment, and signaling transduction. Exogenous application of this element can play a significant role to enhance plant tolerance against Cd toxicity. This chapter reviews the tolerance of A. halimus and A. nummularia saltbushes to Cd stress and the impact of this heavy metal on physiological and biochemical traits. In addition the beneficial role of Ca supplementation to alleviating Cd toxicity in these species was discussed.