Multiwalled Carbon Nanotubes-Jasmonate Interactions Enhance Biomass Production by Regulating Reactive Oxygen Species Homeostasis, δ-Aminolevulinic Acid/Glutamate-1-Semialdehyde Metabolism, Source-Sink Balance, and Defense Responses under Chromium Stress in Soybean

Abstract

Chromium (Cr) contamination severely reduces soybean growth by impairing photosynthesis, nutrient uptake, and osmolyte balance, posing a significant threat to food security. This study evaluated the synergistic effects of multiwalled carbon nanotubes (CNTs) and jasmonic acid (JA) in mitigating chromium (Cr) stress in soybean plants. Chromium stress markedly reduced delta amino levulinic acid (64.33%), Glutamate-1-semialdehyde (66.87%), carotenoids (58.11%), RuBisCo activity (73.01%), and total soluble sugar (48.34%), while increasing oxidative damage as indicated by higher malondialdehyde and electrolyte leakage. Co-application of CNTs and JA effectively mitigated Cr-induced oxidative stress in soybean by reducing hydrogen peroxide and malondialdehyde levels. It also improved SPAD chlorophyll, PSII efficiency, net photosynthetic rate, and transpiration rate, along with increasing flavonoid, protein, and iron content, while lowering Cr accumulation. Chromium stress significantly reduced total phenols (51.11%), flavonoids (57.12%), free amino acids (50.06%), carbon (46.12% & 53.07%), phosphorus (53.34% & 50.22%), copper (39.64% & 41.28%), and zinc (52.03% & 63.74%). However, CNTs and JA application reversed these effects by enhancing total phenols, flavonoids, free amino acids, carbon, phosphorus, copper, and zinc. Additionally, Cr accumulation in both shoots and roots was significantly reduced with CNTs and JA supplementation. Therefore, CNTs and JA mitigated Cr toxicity by improving growth, photosynthesis, antioxidant enzymes activity, and nutritional homeostasis. These findings demonstrate the potential of CNTs and JA as sustainable nano-hormonal based strategy for reducing Cr accumulation in soybean and safeguarding food security.