Heavy metals (HMs) such as cadmium (Cd) and zinc (Zn) disrupt photosynthesis and plant physiology. This study assesses their impact on hydroponically grown industrial hemp (Cannabis sativa) and examines the potential role of silicon (Si) as a protective agent, the latter being known to improve resistance to biotic and abiotic stresses. Various experimental conditions were established, including controls, exposure to Cd and Zn, and treatment with silicon. Physiological effects were assessed by analysing the light response curve, gas exchange and chlorophyll fluorescence, while pigment content was compared using a proteomic approach. The results show a significant decrease in electron transport, net CO2 assimilation, PSII effective quantum yield, transpiration and stomatal conductance. These perturbations reflect stomatal closure as well as altered electron transport under metal stress. In addition, analysis of light saturation highlights a reduction in maximum CO2 uptake and PSII quantum efficiency, as well as an increase in dark respiration in the face of HM stress. Cd and Zn exposure led to a reduction in chlorophyll and carotenoid levels, indicating pigment degradation. The increase in the chlorophyll a/b ratio under metal stress reflects a specific inhibition of chlorophyll b. Contrary to expectations, silicon supplementation did not mitigate the effects of pollutants. These results highlight the negative impact of HMs on the physiology of industrial hemp and reveal the ineffectiveness of silicon as a protective agent in this context. Proteomic analysis provides additional information on the differential accumulation of proteins and the mechanisms underlying the effects of Cd and Zn.
Regnier et al. (Wed,) studied this question.