Unravelling the protective role of silicon in Cannabis sativa hypocotyls under cadmium and zinc stress with imaging and -omics

Abstract

Potentially toxic elements (PTEs) such as cadmium (Cd) and zinc (Zn) are environmental pollutants affecting soil quality and plant growth. Cd is a highly toxic element primarily introduced into the environment through anthropogenic activities. The impact of Cd on plants is particularly severe, as it disrupts cellular metabolism. Zn, conversely, is an essential micronutrient required for several enzymatic functions, including those involved in DNA synthesis, protein production, and oxidative stress regulation. However, excessive Zn levels in soils can lead to toxic effects on plants. The multi-purpose crop hemp (Cannabis sativa L.) has gained attention for its ability to tolerate and accumulate PTEs, including Cd and Zn. In this study, the impact of Cd and Zn with and without the beneficial metalloid silicon (Si) was evaluated on 20-day-old hemp plantlets, focusing on the hypocotyl as a model for bast fibre formation. An integrative approach combining microscopy and multi-omics was applied. The results showed that Cd and Zn impaired bast fibre organisation and disrupted cell wall ultrastructure, causing an altered tissue architecture. Si mitigated these effects by preserving cell wall structure and stabilising secondary wall components. At the molecular level, Si enhanced apoplastic reinforcement through the activation of hemicellulose biosynthesis and cell wall-associated proteins. In addition, Si improved redox homeostasis by stimulating glutathione-dependent detoxification under Cd stress and supported energy metabolism under Zn exposure. Hormonal profiling indicated that Si modulated stress responses by maintaining cytokinin signalling while attenuating ABA- and JA-mediated pathways. The data obtained revealed specific responses at the tissular, ultrastructural and molecular levels, highlighting the beneficial role of Si in mitigating the effects of Cd and Zn.