Analysis of anatomical changes and cadmium distribution in Aegiceras corniculatum (L.) Blanco roots under cadmium stress

Heavy metal stress changes the morphological and anatomical structure of plant organs. In this study, we determined the anatomical changes and Cd distribution in the roots of Aegiceras corniculatum (L.) Blanco (Black mangrove) under Cd stress. The results showed that Cd levels in A. corniculatum root tissues decreased in the following order: endodermis > pith > xylem > epidermis and exodermis > phloem > cortex. The endodermis secondary casparian strip replaces exodermis casparian strip and plays a role in the “retardation mechanism”, which sort of compensates for the missing exodermis retardation effect. The xylem and pith both show high affinity for Cd and contain enriched Cd. This creates a low-Cd environment for phloem and protects the nutrient transport function of the vasculature against Cd toxicity. The present study provides new evidences suggesting that Cd regional enrichment and anatomical structure changes are an adaptive strategy of mangrove plants to HM tolerance. •The endodermis secondary casparian strip participates in “retardation mechanism”.•The endodermis compensates for the missing exodermis retardation effect.•The xylem and pith show high affinity for Cd that in the vasculature.•Xylem and pith protect nutrient transport function of vasculature from Cd toxicity.