The Feedback of Stress Phytohormones in Avena sativa (L.) on Soil Multi-Contamination

As chemical messengers, phytohormones can enhance the tolerance of plants to stress caused by toxic elements (TEs) such as cadmium (Cd), lead (Pb), and zinc (Zn). This study investigated the combined toxicity of Cd, Pb, and Zn, and its impact on stress phytohormones (jasmonates, salicylic acid, and abscisic acid), in oat (<i>Avena sativa</i> L.) using anthropogenically contaminated soil in a 4-week pot experiment. The uptake of TEs by the roots increased in the multi-contaminated soil, while Zn was the only TE to be translocated to the leaves. The toxic effect of the TEs was assessed in terms of plant growth, revealing a decline in leaf dry biomass, whereas the impact on the roots was insignificant. These findings align with the levels of stress phytohormones. An increase in bioactive forms of stress phytohormones in leaves due to TEs indicates TE toxicity and leaf sensitivity. Conversely, low levels of these phytohormones, along with crosstalk between them, suggest reduced defense against TEs in the roots. The abundance of stress phytohormones declined in the following order: salicylic acid > jasmonates > abscisic acid. These results help to understand the mechanism by which plants respond to TEs, particularly their combined toxicity.