Integrated application of cold atmospheric plasma and dopamine mitigates cadmium toxicity by enhancing antioxidant defense and restricting cadmium accumulation in fenugreek (Trigonella foenum-graecum L.)

Cadmium (Cd) toxicity severely restricts plant growth, yet effective strategies for limiting Cd uptake remain limited. This study investigated the effectiveness of integrating cold atmospheric plasma (CAP) seed priming with exogenous dopamine (DA) to enhance Cd tolerance in fenugreek. Factorial ANOVA revealed significant CAP × DA interaction effects for key physiological, biochemical, and molecular traits. Compared with Cd-stressed plants, the combined application of CAP (6 kV for 4 min) and 200 μM DA significantly enhanced root (123%) and shoot growth (75%), fresh and dry biomass, total chlorophyll (140%), relative water content (23%), proline (125%), and flavonoids (106%). The combined treatment also increased ascorbate peroxidase (APX), catalase (CAT), superoxide dismutase (SOD), and polyphenol oxidase (PPO) activities by 123%, 121%, 47%, and 36%, respectively. These responses were associated with a concomitant upregulation in the expression of APX, CAT, SOD, and PPO, reflecting a coordinated activation of the antioxidant defense system at both the transcriptional and enzymatic levels. Consequently, hydrogen peroxide accumulation (40%), malondialdehyde content (44%), electrolyte leakage (42%), and Cd accumulation declined significantly, with Cd concentrations decreasing by 60% in roots and 55% in shoots. The combined treatment also resulted in the highest Cd retention in the growth medium, indicating restricted Cd uptake. FESEM and EDX confirmed plasma-induced physicochemical modifications of the seed surface. Collectively, these findings indicate that CAP and DA strengthen defense systems, mitigate oxidative damage, and are associated with greater Cd retention in the growth medium and reduced Cd accumulation in plant tissues, thereby improving cadmium tolerance in fenugreek.