Heavy metals (HMs) are among the main environmental pollutants that can enter the soil, water bodies, and the atmosphere as a result of natural processes (weathering of rocks, volcanic activity), and also as a result of human activities (mining, metallurgical and chemical industries, transport, application of mineral fertilizers). Plants counteract the HMs stresses through morphological and physiological adaptations, which are imparted through well‐coordinated molecular mechanisms. New approaches, which include transcriptomics, genomics, proteomics, and metabolomics analyses, have opened the paths to understand such complex networks. This review sheds light on molecular mechanisms included in plant adaptive and defense responses during metal stress. It is focused on the entry of HMs into plants, its transport and accumulation, effects on the main physiological processes, gene expressions included in plant adaptive and defense responses during HM stress. Analysis of new data allowed the authors to conclude that the most important mechanism of HM tolerance is extracellular and intracellular HM sequestration. Organic anions (malate, oxalate, etc.) provide extracellular sequestration of HM ions. Intracellular HM sequestration depends not only on a direct binding mechanism with different polymers (pectin, lignin, cellulose, hemicellulose, etc.) or organic anions but also on the action of cellular receptors and transmembrane transporters. We focused on the functioning chloroplasts, mitochondria, and the Golgi complex under HM stress. The currently known molecular mechanisms of plant tolerance to the toxic effects of HMs are analyzed.

Phenolic compounds (PCs) in plants play an important role in growth control and have antioxidant, structural, attractant, signaling and protective functions. Information on the discovery, study and identification of phenolic compounds in plants, their role in the complex system of secondary metabolites has been analyzed and summarized. The functions of PCs at the macromolecular, cellular as well as organism and population levels are described. The pathways of PCs formation, enzymes responsible for their synthesis and the plasticity of the synthesis in a plant cell are highlighted. The involvement of PCs in the plant breathing, photosynthesis, oxidation-reduction processes and regulation of the plants physiological state are discussed.

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