Research on the promotion of tobacco growth and enhancement of stress resistance by molybdenum oxide nanozymes

Nanozymes have exhibited promising application prospects for enhancing stress resistance in agriculture due to their enzyme-mimicking catalytic activities. However, the dose-dependent effects of molybdenum oxide nanozymes in plants and their specific underlying mechanisms under abiotic stress remain unclear. To address the limited efficiency and unclear physiological mechanisms of conventional stress mitigation approaches, this study analyzes the correlation between nanozyme concentrations and key stress-response parameters through physiological and biochemical measurements. It finds that excessive reactive oxygen species (ROS) accumulation under stress is the primary cause of oxidative damage. These stress-induced injuries, which severely impair plant growth, can be effectively alleviated when ROS are scavenged by exogenous nanozymes. A systematic investigation of the applicability of molybdenum oxide nanozymes (MONs) for mitigating salt and drought stresses is then conducted.

This study synthesizes MONs via a hydrothermal method and combines them with a tobacco tissue culture model to explore their mechanism for alleviating salt (100 mmol/L NaCl) and drought (200 mmol/L mannitol) stress, thereby providing a theoretical basis for the application of nanozymes in crop stress resistance. The alleviating effects of MONs on tobacco were evaluated through physiological and biochemical analyses of treated plantlets. The MONs were synthesized using a hydrothermal method with controlled reaction parameters. Tobacco tissue cultures were established from surface-sterilized young leaves on MS medium supplemented with phytohormones. After subculture and rooting, plantlets were transferred to stress-inducing media containing either 100 mmol/L NaCl or 200 mmol/L mannitol. Seven nanozyme concentration gradients—70, 80, 90, 100, 110, 120, and 130 mmol/L—were applied every 2 days over a 7-day treatment period, with stress-only and non-stressed groups serving as controls. Data were preprocessed through tissue homogenization and centrifugation, and targeted biochemical assays were used to determine the physiological indicators. The activities of antioxidant enzymes—including peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD) —as well as malondialdehyde (MDA) and chlorophyll contents, were used to evaluate the physiological responses. All measurements were performed using commercial assay kits according to standard protocols, and each experiment was conducted in triplicate.

The results showed that: (1) under stress conditions, MON treatment markedly elevated the activity of the tobacco antioxidant enzyme system. POD activities in treated groups approached non-stressed control levels (460–480 U/g), whereas stress-only groups showed marked deviations. CAT activity, which was elevated in stress-only plants, generally declined (9.7–14.5 U/g) following nanozyme treatment, indicating that the nanozyme partially substituted for endogenous enzymes by directly scavenging ROS. SOD activity under salt stress recovered from 199.64 U/g in the stress-only group toward the control value of 283.57 U/g. Under drought stress, the elevated SOD activity in stress-only plants (464.47 U/g) decreased toward baseline values after nanozyme treatment; (2) the content of MDA, a key product of membrane lipid peroxidation, was significantly reduced by nanozyme treatment. Under drought stress, a 51.0% reduction was achieved at 110 mmol/L compared with the stress-only control, whereas under salt stress, gradual declines were observed, with the optimal effect at 120 mmol/L; and (3) chlorophyll loss caused by stress (46.3% under salt stress and 83.4% under drought stress) was effectively reversed, and chlorophyll content increased by up to ninefold at 130 mmol/L under drought stress compared with the stress-only control.

These findings suggest that the mechanism of action involves mimicking peroxidase activity to neutralize ROS, reduce oxidative stress, and thereby enhance photosynthetic capacity and stress resistance. By integrating physiological assessments and jointly analyzing multiple stress-response parameters, the correlations between nanozyme concentration and protection against each type of stress can be identified for targeted applications, thereby improving the shortcomings of conventional stress mitigation approaches to a certain extent. The method employed in this study achieved the intended objective, demonstrating that MONs effectively enhance the antioxidant defense system, protect membrane integrity, and preserve photosynthetic pigments under salt and drought stress. This study provides a solid theoretical basis for the application of nanozymes in crop stress resistance and establishes MONs as promising agents for enhancing crop tolerance to adverse environmental conditions.