Research in Plant Metabolites

Research in Plant Metabolites

Investigating the Antioxidant Response of the Cyanobacterium Nostoc sp. as a Biofertilizer under Polyethylene Glycol-Induced Osmotic Stress after Gamma Irradiation

Document Type : Original Article

Authors
Elham Lamizadeh 1
Akbar Hassani 1
Mehdi Nourzadeh Hadad 2
Hasan Etesami 3
1 Department of Soil Science and Engineering, Faculty of Agriculture, University of Zanjan, Zanjan, Iran
2 Nuclear Agriculture Research School, Nuclear Science and Technology Research Institute, Karaj, Iran
3 ³ Faculty of Agricultural Science and Engineering, College of Agriculture and Natural Resources, University of Tehran, Tehran, Iran
10.22034/jrpsm.2026.584825.1117
Abstract
Background and Objective: The cyanobacterium Nostoc sp. is recognized as a valuable biofertilizer in sustainable agriculture due to its capacity for nitrogen fixation, production of bioactive metabolites, and enhancement of soil fertility. However, soil osmotic stress is one of the most critical abiotic stresses that severely limits the growth and performance of these biofertilizers. A novel approach to improving stress tolerance involves the application of physical pre-treatments, such as gamma irradiation, to induce defense mechanisms and establish cross tolerance. The present study was designed to investigate the hypothesis that gamma irradiation can enhance the resistance of Nostoc sp. to osmotic stress through the proactive activation of its antioxidant system. To this end, changes in reactive oxygen species (ROS) levels and the activities of superoxide dismutase (SOD) and peroxidase (POD) in response to the interaction between gamma irradiation and osmotic stress were evaluated.
Materials and Methods: The experiment was conducted as a factorial based on a completely randomized design with three replications. The first factor consisted of gamma irradiation pretreatment at six dose levels (0, 20, 50, 100, 500, and 1000Gy), and the second factor was osmotic stress. ROS levels were quantified using fluorimetry and the DCFH-DA probe. SOD activity was determined based on the inhibition of nitro blue tetrazolium (NBT) reduction, while POD activity was assayed spectrophotometrically using pyrogallol as a substrate. Data were analyzed via two-way analysis of variance (ANOVA) and Tukey’s test at a significance level of p≤0.01.
Results: The results revealed that the main effects of gamma irradiation and osmotic stress, as well as their interaction, on all three biochemical parameters were significant at the p≤0.01 level. In nonirradiated samples, the application of osmotic stress led to a substantial increase in ROS levels (approximately 17-fold compared to the control) and a subsequent decline in SOD and POD activities at high osmotic stress levels. Conversely, prophylactic irradiation at moderate doses (50 and 100Gy) significantly prevented excessive ROS accumulation. The most notable finding was that in samples pre-treated with a 100Gy dose, SOD activity under stress conditions surged from 31.13 to 92.41 units (an approximate 3-fold increase), and POD activity escalated from 12.45 to 74.03 units (an approximate 6-fold increase). Although high irradiation doses (500 and 1000Gy) alone exhibited detrimental effects, when combined with osmotic stress, the samples pretreated with 100Gy demonstrated the optimal protective performance.
Conclusion: The findings of this study indicate that gamma irradiation at moderate doses (50 and 100Gy) can serve as an effective strategy to enhance osmotic stress resistance in the cyanobacterium Nostoc sp. This phenomenon is elucidated by the cross tolerance mechanism. Mild irradiation primes the cell to counteract the severe ROS accumulation induced by osmotic stress through the generation of a basal ROS level and the proactive activation of SOD and POD enzymes. In other words, irradiation triggers an “early warning system” and shifts the cellular tolerance threshold. These findings hold significant practical implications for the production of drought tolerant biofertilizers. Gamma pre-treatment can be implemented as a straightforward and cost effective industrial process to improve the efficacy of Nostoc sp. in saline soils, which comprise a substantial proportion of agricultural lands. Ultimately, this research provides a scientific foundation for the development of a new generation of irradiated biofertilizers capable of tolerating multiple environmental stresses.
Keywords
Biofertilizerو Nostoc sp
Gamma Irradiation
Reactive oxygen species
Superoxide dismutase
Peroxidase
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