Chromium tolerance and detoxification in plants: Uptake, reduction and immobilization mechanisms.

Chromium contamination in soil is of environmental and health concern, with chromate (CrVI) being more toxic than chromite (CrIII). Despite recent progress in understanding Cr-plant interactions, mechanism-centered analysis of plant responses to Cr exposure is lacking. This review explores Cr tolerance and detoxification mechanisms in plants, focusing on Cr uptake, reduction and immobilization. In particular, the review examines the contributions of apoplastic and symplastic pathways to plant Cr uptake, highlighting the role of antioxidants in Cr reduction. Toxic CrVI inhibits plant growth by inducing oxidative stress and impairing plant physiological processes. Plant roots reduce Cr exposure through three barriers: root-exuded organic acids and recruited microorganisms to reduce Cr availability, while the cell wall serves as the primary Cr accumulation site due to its abundant carboxyl groups. Once inside the cells, CrVI is reduced to less toxic CrIII and immobilized by thiol-containing groups or precipitated with anions, while enzymatic and non-enzymatic antioxidants mitigate oxidative damage in plants. This review also discusses strategies to alleviate Cr toxicity by enhancing antioxidant capacity in plants and reducing Cr availability in soil. Overall, elucidating the mechanisms underlying the Cr tolerance and detoxification in plants not only improves crop yield and quality but also facilitates their application in remediation of contaminated soils.