Seed priming versus foliar spraying of biologically synthesized mixed-valence copper oxide(Cu₄O₃): improving...

Climate change is a major global challenge, with soil salinity emerging as a critical factor limiting agricultural productivity. This study reports the biological synthesis of mixed-valence copper oxide (Cu₄O₃) nanoparticles (MVCN) by utilizing Leucaena leucocephala seed extract and copper sulfate as precursors, and evaluates their role in mitigating salinity stress in sunflower (Helianthus annuus L.) plants. The synthesized MVCN were characterized by EDX, XRD, FTIR, UV-Vis, SEM, TEM, and Zeta potential analyses. FTIR confirmed effective capping by seed extract, while SEM revealed spherical particles (13-18 nm) and TEM indicated diverse morphologies, suggesting anisotropic growth.A pot experiment was conducted under 150 mM NaCl stress, with MVCN applied via seed priming or foliar spraying (100 mg/L). Both treatments enhanced plant growth and biochemical traits, with foliar spraying proving more effective. Growth parameters increased significantly: shoot fresh weight (32%), shoot dry weight (50%), shoot length (56%), root fresh weight (65%), root dry weight (35%), and leaf area (30%). Biochemical improvements included chlorophyll a (49%), soluble sugars (45%), soluble protein (30%), oil content (34%), phenolics (31%), and proline (29%). Conversely, Na content and malondialdehyde (MDA) levels decreased by 34% and 46%, respectively, indicating alleviation of salinity-induceddamage.These findings demonstrate that foliar application of biosynthesized MVCN offers a sustainable and promising strategy to enhance crop resilience under salt stress, contributing to improved agricultural productivity in saline environments.