Abstract
BACKGROUND: Global warming severely challenges sweet potato cultivation by disrupting physiological, biochemical, and structural processes. The potential of glutathione-gold nanoclusters (GSH-Au NCs) in enhancing thermotolerance remains largely unexplored in vegetable sweet potato, a key industrial and food security crop. We hypothesized that foliar application of GSH-Au NCs would mitigate heat-induced disruptions in photosynthesis, redox homeostasis, and cellular structures by enhancing antioxidant defenses and enzymatic activities. RESULTS: Under controlled heat stress (42 °C day/35°C night for 7 days), heat stress diminished shoot biomass, leaf area, RWC, and root biomass, while impairing photosynthesis and elevating oxidative damage (H(2)O(2): 276.7% and MDA: 481.5%) and electrolyte leakage by 85.7%. GSH-Au NCs (2 mg L(- 1)) reversed these effects, enhancing growth, shoot and root biomass (45.3% and 28.3%), and RWC (7.9%). These improvements were associated with enhanced photosynthetic efficiency through elevated chlorophyll content (72.6%), Rubisco activity (26.4%), gas exchange parameters (Pn: 86.1% and Gs: 389%), and chlorophyll fluorescence (Fv/Fm: 16.0% and ETR: 48.2%). Mechanistically, GSH-Au NCs correlated with upregulation of ascorbate-glutathione (AsA-GSH) cycle, boosting enzymatic (SOD: 30.1%, APX: 33.6%, and GR: 20.9%) and non-enzymatic antioxidants (AsA/DHA: 33.8% and GSH/GSSG: 29.1%), while lowering oxidative markers: H(2)O(2) (37.8%), MDA (51.7%), and EL (26.8%), compared with heat stressed plants without NCs treatment. Transcriptional upregulation of SOD, APX, GR, DHAR, and MDHAR genes supported these effects. Additionally, GSH-Au NCs enhanced glyoxalase activity (Gly I: 36.9% and Gly II: 35.0%), reducing toxic methylglyoxal (29.3%). Higher proline (51.7%) and secondary metabolites (polyphenols: 38.3% and flavonoids: 62.9%) further strengthen stress resilience. Moreover, GSH-Au NCs restored stomatal behavior and preserved chloroplast and mitochondrial structure. CONCLUSIONS: These findings highlight GSH-Au NCs (2 mg L(- 1)) as a sustainable, cost-effective, eco-friendly nanobiotechnological strategy for mitigating heat stress in sweet potato and promoting climate-resilient horticulture, advancing beyond prior studies on individual GSH or Au nanomaterials by demonstrating the synergetic effects of their combined nanocluster form for the first time in plant species.