Plant Oxidative and Antioxidant Responses to Heavy Metal Stress

Dear Colleagues,

The concentration of hazardous metals, such as Cd, Pb, Cr or Hg, and metalloids, such as As or Se, is reaching threatening levels in agricultural ecosystems, mostly originating from several anthropogenic activities including agriculture. Plants suffer different damages and alterations in key physiological processes, which may constitute the first step of metal(loid) biomagnification in trophic chains that may reach humans, constituting a serious threat for food security. As a result, plant growth is hampered, and numerous symptoms appear upon metal(loid) accumulation in plant cells, with loss of respiration and/or photosynthesis, where impaired electron transfer generates reactive oxygen species (ROS), along with other sources such as plasma membrane-associated NADPH-oxidases (Rboh). To cope with cellular redox imbalance, plants have an intricated antioxidant network that prevents oxidative damages triggered by toxic metal(loid)s, with glutathione (GSH) playing a pivotal role. In addition, GSH is the precursor of phytochelatins, a collection of biothiols able to form stable complexes with metal(loid)s that accumulate harmlessly in vacuoles, the cellular compartments that show high metal(loid) concentrations, along with cell walls. Despite the ample research effort conducted in recent years, little is known about the mechanisms that control antioxidant responses, including glutathione metabolism, which are modulated by endogenous regulators such as abscisic acid, cytokinins, jasmonate or ethylene. On the other hand, significant changes in the biomolecular composition of plant cells occur under metal(loid)-driven oxidative stress, with remarkable alterations in lipid and protein profiles, along with DNA damage and genotoxicity. The activation of cellular mechanisms for recycling damaged components, including controlled ubiquitination and proteasome degradation of non-functional proteins, and/or induction of autophagy, a self-destructive pathway that helps the cell to replace entire damaged organelles, is envisaged. Recent evidence found in crop and model plants, as well as in microalgae, suggests that those recycling processes contribute to metal(loid) tolerance, particularly once ROS accumulate upon exposure to toxic metal(loid)s. Therefore, avoidance of extensive oxidative damage caused by metal(loid)s will help to optimise phytoremediation approaches to clean up polluted soils and waters. In this sense, this Special Issue is proposed to attract the interest of researchers working in the field of plant responses to metals and metalloids, with particular emphasis on the mechanisms related to oxidative stress induction, antioxidant defences and amelioration of ROS accumulation. Researchers are invited to contribute to this Special Issue with original research and review articles on the oxidative stress alteration caused by toxic metals and metalloids, including changes in subcellular components, metal(loid) compartmentation and complexation, biochemical and physiological alterations and “omics” approaches, to broaden our current knowledge on tolerance and stress avoidance mechanisms.

Dr. Luis E. Hernandez
Dr. Cristina Ortega Villasante
Guest Editors

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• antioxidants
• autophagy
• biothiols
• cellular damage
• compartmentation
• glutathione
• metals
• metalloids
• oxidative stress
• phytochelatins
• phytoremediation
• reactive oxygen species
• tolerance