Compared to antioxidants and polyamines, the role of maize grain-derived organic biostimulants in improving cadmium tolerance in wheat plants

Abstract

Recently, the strategy of seed soaking has been successfully applied using extracts from different plant parts for healthy growth of plant under different environmental stresses. Compared to antioxidants like ascorbic acid (AsA) and glutathione (GSH) or polyamines (PAs) like spermine (SPM), spermidine (SPD), and putrescine (PUT), the effects of seed soaking using maize grain extract (MGE) on the biomass, productivity, phytohormones, and antioxidant defense system and its different components were examined with Cd²⁺-stressed wheat plants. In a preliminary study, seed soaking using AsA + GSH or PUT + SPD + SPM was more effective in increasing shoot fresh and dry weights, SPAD chlorophyll, and grain yield, and reducing malondialdehyde (MDA) content than individuals. In addition, MGE at 2% was more efficient than other concentrations. Therefore, they were selected for the main study. In the main study, compared to the control, seed soaking in AsA + GSH, PUT + SPD + SPM or MGE had positive effects on plant growth, yield, photosynthetic efficiency, contents and redox states of AsA and GSH, contents of PAs and plant hormones to varying degrees. Proline content and its metabolism enzymes activity, contents of soluble protein, N-compounds, soluble sugars, and α-tocopherol (α-TOC), and activities of antioxidant enzymes were not affected. However, contents of MDA and hydrogen peroxide (H₂O₂) were significantly reduced under normal conditions. Under Cd²⁺ stress (1.2 mM), along with the detrimental increases in the contents of MDA, H₂O₂ and Cd²⁺, contents of N-compounds, soluble sugars, proline content and its metabolism enzymes activities, AsA and GSH and their redox states, and polyamines, and activities of antioxidant enzymes were increased. In contrast, plant growth and yield, photosynthetic efficiency, soluble protein, and plant hormones were significantly reduced compared to the control. However, all of these attributes were significantly improved to varying degrees along with reduced contents of Cd²⁺, MDA, and H₂O₂ by seed soaking in AsA + GSH, PUT + SPD + SPM or MGE compared to the Cd²⁺-stressed control. Compared to AsA + GSH or PUT + SPD + SPM, seed soaking in MGE at 2% conferred the best results. Therefore, it is recommended to soak wheat seeds using MGE to improve plant growth and productivity by restricting the inhibitory influences of oxidative stress induced by Cd²⁺ stress.

Keywords: Antioxidant reducing power; Cadmium stress; Defense systems; Plant hormones; Proline and metabolism enzymes; Wheat productivity.