Endophyte mediated delivery of methionine-functionalized hydroxyapatite nanoparticles for stress alleviation in Zea mays L.

Drought stress is a major abiotic constraint to maize (Zea mays L.) productivity, especially in arid and semi-arid regions of the world. This study aimed to investigate the potential of methionine-functionalized hydroxyapatite nanoparticles (Met-HANPs), alone and with endophytic fungi isolated from the tubers of Solanum tuberosum L., to enhance drought tolerance under polyethylene glycol (PEG) induced osmotic stress (0, -0.2, -0.4, -0.6 MPa). Methionine capped hydroxyapatite nanoparticles (Met-HANPs) were synthesized via co-precipitation using calcium nitrate, disodium phosphate, and methionine (pH 11). Characterization confirmed successful synthesis where X-diffraction (XRD) revealed a pure hexagonal phase (a = 9.22 Å, c = 6.885 Å), Fourier Transform Infrared Spectroscopy (FTIR) detected functional groups associated with methionine and phosphate groups, Scanning Electron Microscopy (SEM) showed particle sizes of 104–377 nm, and Energy Dispersive X-ray Spectroscopy (EDX) verified elemental composition. A greenhouse experiment (randomized block design) assessed the treatments’ effects on germination, growth, and biochemical traits. Met-HANPs, particularly with endophytes, significantly improved drought resilience. Final Germination Percentage rose from 53% (control) to 96% (Met-HANPs) and 98% (Met-HANPs + endophytes); Seed Vigor Index increased from 480 to 2295. Growth metrics such as Absolute Growth Rate (AGR), Relative Growth Rate (RGR), and Crop Growth Rate (CGR) were markedly higher under treatment. Photosynthetic pigment content also improved, with chlorophyll a reaching 3.02 mg/g fresh weight (FW) versus 1.06 mg/g FW in control. Proline content, a key stress marker, rose from 1.75 to 7.29 µmol/g FW. Antioxidant enzyme activities (Superoxide Dismutase (SOD), Peroxidase (POD), Catalase (CAT), Ascorbate Peroxidase (APOX) increased significantly under Met-HANPs + endophytes, indicating enhanced oxidative stress defense. These findings suggest that Met-HANPs, especially in synergy with endophytes, can substantially improve maize performance under drought, offering a promising approach for climate-resilient agriculture.