Special Issue on "Metallophytes for soil remediation" - Preface

Heavy Metals, Their Phytotoxicity, and the Role of Phenolic Antioxidants in Plant Stress Responses with Focus on Cadmium: Review

The current state of heavy metal (HM) environmental pollution problems was considered in the review: the effects of HMs on the vital activity of plants and the functioning of their antioxidant system, including phenolic antioxidants. The latter performs an important function in the distribution and binding of metals, as well as HM detoxification in the plant organism. Much attention was focused on cadmium (Cd) ions as one of the most toxic elements for plants. The data on the accumulation of HMs, including Cd in the soil, the entry into plants, and the effect on their various physiological and biochemical processes (photosynthesis, respiration, transpiration, and water regime) were analyzed. Some aspects of HMs, including Cd, inactivation in plant tissues, and cell compartments, are considered, as well as the functioning of various metabolic pathways at the stage of the stress reaction of plant cells under the action of pollutants. The data on the effect of HMs on the antioxidant system of plants, the accumulation of low molecular weight phenolic bioantioxidants, and their role as ligand inactivators were summarized. The issues of polyphenol biosynthesis regulation under cadmium stress were considered. Understanding the physiological and biochemical role of low molecular antioxidants of phenolic nature under metal-induced stress is important in assessing the effect/aftereffect of Cd on various plant objects-the producers of these secondary metabolites are widely used for the health saving of the world's population. This review reflects the latest achievements in the field of studying the influence of HMs, including Cd, on various physiological and biochemical processes of the plant organism and enriches our knowledge about the multifunctional role of polyphenols, as one of the most common secondary metabolites, in the formation of plant resistance and adaptation.

The effect of interactions between soil compaction and phenol contamination on plant growth characteristics: Implications for scaling bioremediation at industrial sites

In phenol contaminated soils from an industrial site, soil compaction and soil chemical contaminants influenced germination, emergence, and early plant growth (roots and shoots) for Thrift (Ameria maratima) and Blackbutt oats (Avena sativa). The specific effects were of soil compaction (low, 100 psi and high, 800 psi) at two concentrations of phenol (biotreated, ∼200 mg kg^-3; untreated, ∼1150 mg kg^-3). Plant responses to compaction and phenol varies between the two species. Emergence of Thrift showed greater sensitivity to increasing soil compaction but only under high phenol concentrations. Low phenol inhibited Thrift root length, as is the case with Balckbutt oats, although high phenol had no significant impact on Thrift. While shoot length of Blackbutt oats is not significantly affected by increasing soil compaction, it is negatively impacted at the increased phenol concentrations in the untreated soils indicating an interaction effect with compaction. This is the first study that examines the impact of soil contamination on oats. The oat variety tested had known drought tolerance and hardiness indicating an ability to withstand compaction, and which may explain those characteristics. Thrift was most resistant to contamination which is consistent with its previously reported tolerance of pollutants. Implications of the study are that Blackbutt oats represent a potential candidate species for land rehabilitation under high compaction conditions such as at degraded soil sites at decommissioned mining operations, polluted industrial sites, or degraded (compacted) agricultural land.