Calcium regulates the physiological and molecular responses of Morus alba roots to cadmium stress

Heavy metal cadmium (Cd) is toxic to organisms. Mulberry (Morus alba L.) is a fast-growing perennial that is also an economical Cd phytoremediation material with large biomass. However, the molecular mechanisms underlying its Cd tolerance remain unclear. Here, we reveal the physiological and molecular mechanisms underlying Cd toxicity under varying calcium (Ca) treatments. First, under low-Ca treatment (0.1 mM Ca), mulberry growth was severely inhibited and the root surface structure was damaged by Cd stress. Second, electrophysiological data demonstrated that 0.1 mM Ca induced an increased Cd2+ influx, leading to its accumulation in the entire root and root cell walls. Third, high-Ca treatment (10 mM Ca) largely alleviated growth inhibition, activated antioxidant enzymes, increased Ca content, decreased Cd2+ flux, and inhibited Cd uptake by roots. Finally, 0.1 mM Ca resulted in the activation of metal transporters and the disruption of Ca signaling-related gene expression, which facilitated Cd accumulation in the roots, aggravating oxidative stress. These adverse effects were reversed by treatment with 10 mM Ca. This study preliminarily revealed the mechanism by which varying Ca levels regulate Cd uptake and accumulation in mulberry roots, provided an insight into the interrelationships between Ca and Cd in the ecological and economic tree mulberry and offered a theoretical basis for Ca application in managing Cd pollution. [Display omitted] •Ca reduces Cd accumulation in the root cell wall of mulberry seedlings.•Cd2+ influx is inhibited by Ca in mulberry root meristem zone.•Enzymatic antioxidant system is activated by Ca in response to Cd-induced oxidative stress.•Low Ca treatment increases PME activity under Cd stress in mulberry root.•High Ca treatment weakens RBOHD expression under Cd stress in mulberry root.