Effect of modified light spectra on cadmium uptake and root exudation of tomato and mustard plants

Phytoremediation is a widely used and effective method for removing cadmium (Cd) from contaminated soils. Recent studies suggest that modifying the light spectrum during plant growth can improve their heavy metal uptake and tolerance. However, further research is needed to understand the variations among plant species and their biochemical responses to Cd stress under different light spectra. This study examined the impact of high blue/red photon flux ratio (B light) compared to full-spectrum white light (FS-light) on cadmium uptake, plant physiology, and root exudation in tomato (Solanum lycopersicum) and Indian mustard (Brassica juncea). Tomato plants exhibited significant physiological changes under different light treatments, with B light resulting in greater Cd accumulation in roots and reduced biomass. A detailed analysis of root exudates showed that Cd-induced metabolites were produced under both FS and B light conditions. Cadmium-induced exudates included steroidal saponin, tomatine, and predicted spirostane triterpenoids. Light spectrum-specific exudates comprised amino acids, terpenes, peptides, fatty acids, and phenylpropanoids. These metabolites were significantly upregulated under FS light conditions but diminished or absent under B light. Mustard was less affected by light spectrum changes. While it showed reduced plant height under B light, biomass and root exudation remained relatively unaffected. This study revealed a plant species-specific response to B light and Cd stress and underscores the potential application of tailored light spectra to optimize Cd phytoremediation and to manipulate root metabolite exudation profiles.