ZnO and rGO-Based nanoparticles regulate morphophysiological, biochemical, and molecular responses of Phaseolus vulgaris L. under drought and arsenic stress.

Combined arsenic and PEG-induced osmotic stress markedly impaired growth, water status, oxidative balance, and stress-associated metabolism in two Phaseolus vulgaris genotypes (G-53 and G-68). Relative to the non-stressed control, combined stress reduced SPAD values by 6.9% in G-53 and 6.0% in G-68, while increasing cell membrane damage (CMD) by 44.3% and 33.8%, and malondialdehyde (MDA) by 51.0% and 107.1%, respectively. Arsenic accumulated predominantly in roots, whereas nutrient balance and transcriptional responses varied according to genotype and treatment. Plants were pretreated with foliar 0.5% ZnSO4, rGO, ZnO, or rGO-ZnO nanoparticles (NP) and subsequently exposed to single or combined stress conditions. Across the evaluated traits, rGO-ZnO was most frequently associated with attenuation of stress injury. Under combined stress, rGO-ZnO reduced CMD by 19.3% in G-53 and 44.2% in G-68 and reduced MDA by 40.4% and 61.5%, respectively, relative to the corresponding stressed controls. The same treatment increased proline from 1.57 to 2.39 µmol mL− 1 in G-53 and from 0.80 to 3.25 µmol mL− 1 in G-68. RT-qPCR analysis further indicated treatment- and genotype-dependent variation in the relative transcript abundance of genes related to metal transport, signaling, and photosynthetic metabolism. Overall, Zn-based materials, particularly rGO-ZnO NPs, were associated with partial alleviation of combined stress effects; however, treatment-related changes in arsenic partitioning indicate that agronomic relevance should be evaluated alongside food-safety considerations.