Document Type : Research Paper - Plant Physiology
Authors
1 Department of Horticultural Sciences, Garmsar Branch, Islamic Azad University, Garmsar, Iran .
2 Department of Biology, Garmsar Branch, Islamic Azad University, Garmsar, Iran
Abstract
Introduction
There is no doubt that significant progress is being made in nanoscience and technology, which has paved the way for advancements in many different fields such as agriculture, biology, food, and medicine. Among the different types of nano-scaled metal oxides, zinc oxide nanoparticles (ZnONPs) are among the most widely employed nano-compounds in various industries, including agriculture, food, and medicine. Nitric oxide (NO) is a bioactive signaling substance in living organisms, including plants, which plays vital roles in different stages of plant development during the life cycle. Physiological responses of crop plants to long-term application of NO or ZnONPs individually and mixed manners have not been well investigated and remain largely unknown. The purpose of this research is to investigate the effect of long-term foliar application of NO or ZnONPs on the growth performance and physiology of tomato plants. Considering the necessity of developing a sustainable agricultural approach, this project was designed to evaluate the effect of long-term foliar application of NO or ZnONPs on the growth, performance, nutrition and metabolism of tomato plants.
Materials and methods
This study was implemented as a completely randomized design with four treatment groups and three independent replications. This experiment was conducted in soilless conditions (cocopeat and perlite) in a greenhouse (Islamic Azad University, Garmsar branch, Garmsar). Tomato seedlings was irrigated with Hoagland nutrient solution. 30-day-old tomato seedlings were sprayed with ZnO-NP at two concentrations (0 and 3 mg/L) or NO (0 and 25 μM) 15 times with an interval of 72 hours.
Results and Discussion
The results showed that NO and ZnONPs treatments, especially in the combined one, caused a significant increase in the biomass in shoot and root compared to the control. The applied treatments also affected the characteristics of the plants in the reproductive stage. The application of NO and ZnONPs treatments significantly reduced the time of entering into the reproductive phase, increased fruit production, and enhanced fruit biomass, which indicated the effectiveness of these treatments on plant reproductive development. Foliar spraying with NO and ZnONPs caused a significant improvement in the content of several essential minerals, including potassium (K+), iron (Fe) and zinc (Zn) in both leaves and fruits, compared to the control group. The NO and ZnONPs treatments synergistically and significantly augmented in the concentrations of photosynthetic pigments, including chlorophyll a (Chl a), chlorophyll b (Chl b), and carotenoids in leaves in comparison to the control group. The highest amount of proline amino acid was observed in ZnONP and NO+ZnONP treatment groups, which was significantly higher than the control group. Single and combined treatments of seedlings with NO and ZnONPs led to a significant increase in the content of soluble phenols in leaves compared to the control group. Phenylalanine ammonia lyase (PAL) enzyme activity also followed the same trend as soluble phenols. Also, the activity of antioxidant peroxidase enzyme showed a significant up-regulation in response to the application of NO or ZnONPs. The highest activity of nitrate reductase enzyme was recorded in the leaves of plants simultaneously supplemented with NO and ZnONPs.
Conclusion
The results of this research indicated that foliar spraying with NO or ZnONPs at low concentration can lead to the promotion of plant growth and metabolism and also strengthening the plant's defense system, while reducing the risk of possible toxicity. These findings can be useful for designing future studies on nano-fertilizers or pesticides. This study also emphasizes the necessity of providing transcriptome and proteome data in future studies
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