Molecular Mechanisms of Metal Toxicity and Plant Tolerance
A special issue of International Journal of Molecular Sciences (ISSN 1422-0067). This special issue belongs to the section "Molecular Plant Sciences".
Deadline for manuscript submissions: closed (30 December 2022) | Viewed by 12738
Special Issue Editor
Interests: plant ecophysiology; biotic stress; abiotic stress; photosynthesis; antioxidative mechanisms; photoprotective mechanisms; mineral nutrition; ROS
Special Issues, Collections and Topics in MDPI journals
Special Issue Information
Dear Colleagues,
Increased industrial and agricultural human activities, such as mining and smelting, electroplating, wastewater irrigation, and chemical fertilizers, have resulted in high environmental concentrations of toxic metals. It is now well recognized that the increased concentrations of some non-essential metals such as Cd, Pb, or Cr accumulate in the environment and subsequently become toxic to all living organisms. Environmental pollution by toxic heavy metals is growing worldwide and poses an increasing hazard to the environment and human health.
Plants growing on metal-polluted sites possess tolerance for high metal concentrations by restricting the metal transport to the aerial tissues. However, some plant species can accumulate metals at very high concentrations in their aerial parts and are called hyperaccumulators. For example, foliar Cd concentrations above 100 μg g−1 dry biomass (0.01%) are considered extraordinary and a threshold value for Cd hyperaccumulation. Hyperaccumulators that can be used for phytoremediation of anthropogenically heavy metal-contaminated soils—and also for phytomining, which is the commercial extraction of high-value metals from metal-rich soils—are plant species that actively take up heavy metals, translocate them into the aerial parts, and isolate them into an unhazardous form that is not detrimental to vital enzymes and especially photosynthesis. Plant metabolites with metal chelating ability are crucial in mediating the adaptation of plants to the excess of heavy metals and supporting the uptake of metals in hyperaccumulator species, providing a tool for increased phytoremediation.
Plants have developed various exclusive and effective mechanisms for heavy metal detoxification and tolerance, including control of the metal influx and acceleration of the metal efflux, metal chelation and sequestration, metal remobilization, and scavenging of metal-induced overproduction of reactive oxygen species (ROS). Unlike redox-active metals such as Fe and Cu, other metals (e.g., Pb, Cd, Ni, Mn, Al and Zn) cannot generate ROS directly, only via different indirect mechanisms.
Reactive oxygen species (e.g., O2•–, H2O2, OH•, 1O2) are partly reduced or activated forms of atmospheric oxygen (O2). In plant cells, they are constantly formed by the unavoidable leakage of electrons onto O2 from the energy metabolism activities in chloroplasts, mitochondria, and peroxisomes or in plasma membranes, or as byproducts in the various metabolic pathways located in diverse cellular parts. Metal-induced ROS accumulation is scavenged by enzymatic antioxidants, such as superoxide dismutase (SOD), ascorbate peroxidase (APX), monodehydroascorbate reductase, (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), glutathione peroxidase, (GPX), guaicol peroxidase (GOPX), glutathione-S- transferase (GST), and catalase (CAT), as well as non-enzymatic metabolites, such as ascorbic acid, glutathione, a-tocopherol, carotenoids, phenolic compounds, flavonoids, and proline.
Although ROS were initially believed to be toxic byproducts of an aerobic metabolism that must be scavenged to avoid oxidative damage to the cell, it is now widely accepted that ROS are used by most organisms as crucial signal transduction molecules that at basal levels are essential to sustain life. ROS regulate several processes such as the cell cycle, plant growth and development, systemic signaling, programmed cell death, abiotic stress responses, and pathogen defense.
Disturbances in the electron transport, enzymatic activities involved in CO2 fixation, or stomatal closure may result in a metal-induced decrease in photosynthetic efficiency. Photosystem II (PSII) is extremely sensitive to heavy metal toxicity that exerts multiple effects on both donor (inhibition of oxygen evolution) and acceptor sites (inhibition of electron transfer from quinone A (QA), to quinone B (QB). Since plant production is driven by photosynthesis, by assessing heavy metal’s influence on the rate of photosynthesis we can estimate the molecular mechanisms of metal toxicity and plant tolerance.
In this Special Issue of the International Journal of Molecular Sciences, we expect to publish a collection of papers on the recent advances in Molecular Mechanisms of Metal Toxicity and Plant Tolerance.
Prof. Dr. Michael Moustakas
Guest Editor
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Keywords
- Hyperaccumulator species
- Phytoremediation
- Phytochelatins
- Metal detoxification
- Metal uptake
- Metal transporters
- Ηeavy metal tolerance
- Metal remobilization
- Metal-induced ROS
- Metalloproteins
- Metal deficiencies
