An Overview of the Mechanisms through Which Plants Regulate ROS Homeostasis under Cadmium Stress

Abstract

Cadmium (Cd²⁺) is a non-essential and highly toxic element to all organic life forms, including plants and humans. In response to Cd stress, plants have evolved multiple protective mechanisms, such as Cd²⁺ chelation, vesicle sequestration, the regulation of Cd²⁺ uptake, and enhanced antioxidant defenses. When Cd²⁺ accumulates in plants to a certain level, it triggers a burst of reactive oxygen species (ROS), leading to chlorosis, growth retardation, and potentially death. To counteract this, plants utilize a complex network of enzymatic and non-enzymatic antioxidant systems to manage ROS and protect cells from oxidative damage. This review systematically summarizes how various elements, including nitrogen, phosphorus, calcium, iron, and zinc, as well as phytohormones such as abscisic acid, auxin, brassinosteroids, and ethylene, and signaling molecules like nitric oxide, hydrogen peroxide, and hydrogen sulfide, regulate the antioxidant system under Cd stress. Furthermore, it explores the mechanisms by which exogenous regulators can enhance the antioxidant capacity and mitigate Cd toxicity.

Keywords: antioxidant enzymes; antioxidants; cadmium; reactive oxygen species; regulatory mechanism.

Figure 1

Antioxidant systems involved in the response to Cd stress. Abbreviations: superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; peroxidase, POD; guaiacol peroxidase, GPX; glutathione reductase, GR; dehydroascorbate reductase, DHAR; monodehydroascorbate reductase dehydroascorbate, MDHAR; ascorbic acid, AsA; glutathione, GSH; glutathione oxidized, GSSG; phytochelatins, PCs; MTs, metallothioneins; monolignols, ML; oxidized monolignols, oxML; dehydroascorbate, DHA; monodehydroascorbate, MDHA.

Figure 2

Regulation of antioxidant enzyme activities and antioxidant content by mineral elements, plant growth regulators, and signal molecules.The regulation of the catalytic activity of key antioxidant enzymes involved in induced oxidative stress—such as SOD, CAT, APX, POD, MDHAR, DHAR, GPX, and GR—as well as the levels of major non-enzymatic antioxidants, including GSH, AsA, proline, flavonoids, carotenoids, and phenolics, is influenced by various mineral elements, plant growth regulators, and signaling molecules. Abbreviations: superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; peroxidase, POD; guaiacol peroxidase, GPX; glutathione reductase, GR; dehydroascorbate reductase, DHAR; monodehydroascorbate reductase dehydroascorbate, MDHAR; ascorbic acid, AsA; glutathione, GSH; indole-3-acetic acid, IAA; gibberellin, GA; jasmonic acid, JA; brassinosteroids, BRs; abscisic acid, ABA; salicylic acid, SA; ethylene, ETH; strigolactone, SL; melatonin, MLT; hydrogen peroxide, H₂O₂; hydrogen sulfide, H₂S; nitric oxide, NO.

Figure 3

Regulation of Cd²⁺ absorption by various elements, plant growth regulators, and signal molecules. Abbreviations: indole-3-acetic acid, IAA; gibberellin, GA; jasmonic acid, JA; brassinosteroids, BRs; abscisic acid, ABA; salicylic acid, SA; ethylene, ET; strigolactone, SL; melatonin, MLT; polyamines, PAs; hydrogen peroxide, H₂O₂; nitric oxide, NO.