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BACKGROUND Heavy metal pollution caused by the exploitation of mineral resources in the social development has caused serious threats to the ecosystem and human health. Hyperaccumulating plants have super-enrichment and super-tolerance capabilities for heavy metals, which is an effective way to reduce environmental heavy metal pollution, protect human health, and realize green mineral exploration. It has been widely used in phytoremediation, plant mining and plant prospecting. OBJECTIVES To better understand the enrichment and tolerance mechanisms of hyperaccumulating plants, reveal the principles of heavy metal-plant interactions, and improve the ability of plants to accumulate heavy metals. METHODS Based on a brief description of the effects of heavy metals on plants, the focus of this article is the accumulation mechanism of heavy metal hyperaccumulation plants, and a review of the progress in the fields of detoxification and tolerance mechanisms. RESULTS (1) The root exudates of hyperaccumulator and microorganisms work together to promote the dissolution of heavy metals. After being absorbed by the symplastic and apoplastic pathways, the heavy metals are transported upwards to aerial parts through xylem, and segregated in vacuoles, achieving the hyperaccumulation of heavy metals. (2) Concentration of free metal ions in cytoplasm can be reduced by combining heavy metals with small molecular organic acids, cell walls, phytochelatins and vacuole isolation, which increases plant tolerance. (3) Under heavy metal stress, plants activate a variety of specific antioxidant enzymes to resist oxidative stress and achieve hypertolerance on heavy metals. (4) A possible mechanism is suggested that arsenic-induced oxidative stress in plants should be composed of arsenic reduction and methylation, and Haber-Weiss reaction. CONCLUSIONS In-depth research on the physiological and biochemical processes involved in hyperaccumulation and hypertolerance of hyperaccumulator reveals key factors and related principles. Finding effective ways to improve their specific accumulation and indication capabilities will contribute to the research and application of hyperaccumulators to develop in depth. |
