Introduction: The plant species Cyamopsis tetragonoloba L. (Fabaceae) is a source of guar gum that has a variety of applications in the pharmaceutical industry because of its therapeutic properties. Other parts of the plant are also used as food and fodder. This study was conducted to evaluate some physiological changes and gum production of guar in response to foliar spraying with synthesized zinc oxide nanoparticles (ZnO-NPs).Methods: ZnO-NPs were synthesized using guar gum by the co-precipitation method. The properties of the ZnO-NPs were investigated using various analytical techniques, including ultraviolet-visible spectroscopy (UV-Vis), scanning electron microscopy (SEM), transmission electron microscope (TEM), energy dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The nanoparticles were sprayed on the leaves of the Saravan landrace of guar to study their effects on the physiological properties of the plant. The experiments were performed in a completely randomized design with three replications.Results: Treatment of plants with ZnO-NPs resulted in an improvement of some physiological properties. After exposure to 500 mg/L of ZnO-NPs, the contents of chlorophyll a, chlorophyll b, total chlorophyll, carotenoids, gum, and soluble protein were increased by 47.88%, 78.43%, 54.37T, 29.41%, 55.08%, and 52.12%, respectively. Additionally, the amount of Zn and insoluble sugars showed the highest increase, by 3.96 and 4.31 times, respectively. In contrast, soluble sugars content as well as the activity of catalase (CAT), peroxidase (POX), and ascorbate peroxidase (APX) reduced 0.69-, 2.23-, 1.60-, and 3.91-fold, respectively.Conclusion: ZnO-NPs improved the physiological properties of guar at different concentrations, with the best effects obtained at the maximum concentration of 500 mg/L. The results of this study suggest that the ZnO-NPs synthesized by the biocompatible process are appropriate candidates to prepare guar gum to be used in pharmaceutical and therapeutic-based approaches.
Keywords: ascorbate peroxidase, chlorophyll, Cyamopsis tetragonoloba, guar gum, nanoparticles, zinc oxide