Exogenous Putrescine Modulates Variety-Specific Cadmium Tolerance in Wheat Seedlings: Synergistic Roles of Antioxidant Defense and Physiological Homeostasis

Dandan Zhong¹Haili Yan¹Xinxia Chen¹Ziyu Zhong²Xuerui Li²Xiangzhen Jia²Siyu Chang²Jie Shen^2*Dongxu Zhang^1*

• ¹Millet Research Institute, Shanxi Agricultural University, Changzhi, China
• ²Changzhi University, Changzhi, China

Cadmium (Cd) contamination in farmland is a significant environmental issues affecting crop yields. Putrescine (Put), a polyamine compound, functions as a signaling molecule that actively mediates plant responses to environmental adversities. Wheat exhibits a distinctive propensity for translocating the heavy metal Cd into its seeds compared to other crops, which poses a critical environmental adaptation challenge that needs to be addressed in agricultural systems. This study employed Changmai 4013 (Cd-tolerant) and Chang 6475 (Cd-sensitive) varieties as test materials to investigate the regulatory effect of exogenous Put treatment on the Cd tolerance of both varieties under Cd stress. Wheat seeds were soaked in 0.05, 0.1, 0.2, 0.4, 0.8, and 1.6 mM Put solution, and then cultured in a 80 mg·L−1 Cd solution. The results indicated that Cd stress significantly inhibited wheat germination and seedling vigor. However, exogenous Put treatment effectively alleviated the stress-induced damage. It reduced malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) content, decreased relative electrical conductivity, increased catalase (37.4%), glutathione (39.47%), and relative water content (30.67%), promoted the synthesis of osmotic regulators, reduced Cd accumulation in roots and shoots, and promoted growth. Exogenous Put also significantly increased the endogenous levels of spermidine (Spd), spermine (Spm), and Put in both cultivars. Significant cultivar differences were observed in the response, as polyamine levels in Changmai 4013 peaked at the 0.1 mM Put treatment, while Chang 6475 showed the most significant increase in endogenous Put content at the 0.2 mM Put treatment. A comprehensive evaluation using the Membership Function (MV) method indicated that the 0.1 mM Put treatment provided the best overall alleviation effect for both cultivars. Multivariate analysis revealed distinct mitigation mechanisms between the two cultivars. Changmai 4013 primarily relied on maintaining physiological homeostasis, whereas Chang 6475 depended on enhancing the antioxidant system. Furthermore, the latter exhibited a stronger demand for and utilization capacity of exogenous Put. These findings provide an important theoretical basis for wheat cultivar selection in Cd-contaminated areas and the precision field application of Put.