Plant Response to Toxic Metals: Emerging Sources, Phytohormone Role, and Tolerance Responses

Abstract

The availability of toxic metals in the soil system is an important limiting factor for global crop productivity, being considered a major threat to food security. In the last years, vast areas of arable land around the world have been polluted by toxic heavy metals such as arsenic (As), cadmium (Cd), and lead (Pb), and the high accumulation of these elements in edible plants is causing severe damages to the health of humans and animals. Soil acidification, for many reasons, can turn the most abundant metal in the soil, aluminum (Al), also toxic for plants. A large number of different transporters, enzymes, and ligands, as well as their related genes, which play an important role in uptake, translocation, subcellular compartmentalization, and detoxification of different toxic metals, have been implicated in how plants respond and survive. Between metal perception and response, multiple signaling pathways are triggered, in which hormone participation has been evidenced and clarified. In this chapter, we provide an overview about the interaction between the main molecular components shared between major toxic metal(loid)s, such as As, Cd, Pb, and Al, and plant hormone pathways, focusing on abscisic acid (ABA), discussing interesting topics which raise perspectives for plant tolerance bioengineering.