Document Type : Research Article
Authors
1 Department of Horticulture, Faculty of Agriculture, University of Bou Ali sina, Hamedan, Iran
2 Soil and Water Research Department, Chaharmahal and Bakhtiari Agricultural and Natural Resources Research and Education Center, Agricultural Research, Education and Extension Organization (AREEO), Shahrekord,Iran
3 Horticulture Crops Research Department, Natural Resources Research and Education Center of Chaharmahal and Bakhtiari, AREEO, Shahrekord, Iran
Abstract
Vegetables are among the most important agricultural products in Iran, holding significant importance in terms of production and consumption. These products, in addition to meeting nutritional needs, play a crucial role in public health. Due to their high nutritional value, fiber content, and antioxidant compounds, the consumption of vegetables has always been emphasized by nutritionists and is increasing. In healthy diets, regular consumption of vegetables is recommended as a rich source of vitamins, minerals, and antioxidants. However, one of the main challenges associated with vegetable consumption is the nitrate content, which can have adverse effects on human health.Nitrate is a natural compound in plants that is primarily absorbed from the soil and accumulates in plant tissues. Under normal conditions, small amounts of nitrate are essential for plant growth, but excessive accumulation can pose serious health risks. Overconsumption of nitrate may lead to diseases such as methemoglobinemia (blue baby syndrome), which is particularly dangerous for infants. Additionally, some studies have suggested that excessive nitrate intake may be linked to an increased risk of certain cancers. Therefore, controlling nitrate levels in agricultural products and finding effective methods to reduce its accumulation in plants is of great importance.Selenium, due to its effects on plant growth and its role in antioxidant systems, is an essential micronutrient for human health. This element plays a crucial role in boosting the immune system, preventing oxidative stress, and reducing the risk of chronic diseases. In plants, selenium acts as a growth regulator and influences various metabolic processes. Numerous studies have shown that selenium can reduce nitrate accumulation in plants and improve nitrogen uptake and utilization efficiency. This highlights the significance of investigating the effects of selenium on nitrogen metabolism and nitrate levels in plants.In this study, the effect of sodium selenite and calcium nitrate foliar application on certain growth characteristics, biochemical properties, nitrate and selenium content, and nitrate reductase enzyme activity in spinach was investigated. Spinach is one of the most widely consumed leafy vegetables due to its high iron, vitamin C, and antioxidant compound content, making it highly nutritious. The treatments included foliar application of calcium nitrate (5, 10, and 20 mM), sodium selenite (0.5, 1, and 1.5 mM), and a control (distilled water). Foliar application is a commonly used method in plant nutrition management due to its rapid absorption and direct impact on plant physiology. After the growth stage (8–10 leaf stage), growth indices, biochemical compounds, nitrate and selenium content, and nitrate reductase activity were measured.The results indicated that foliar application of sodium selenite and calcium nitrate significantly affected chlorophyll a, b, total chlorophyll, and carotenoid content. An increase in chlorophyll content suggests improved photosynthesis and light absorption efficiency in plants. Additionally, the highest total phenol content, antioxidant activity, and nitrate reductase activity were observed in the 20 mM calcium nitrate and 1.5 mM sodium selenite treatment. Phenolic and antioxidant compounds play a crucial role in protecting plant cells against environmental stresses and pathogens. Therefore, increased antioxidant activity in plants can also enhance the nutritional quality and shelf life of the final product.The highest nitrate content was observed in the control, while the highest selenium concentration was found in the 1.5 mM sodium selenite treatment. These findings suggest that selenium application can reduce nitrate levels and improve the nutritional quality of spinach. Since excessive nitrate accumulation in leafy vegetables can endanger consumer health, adopting effective methods to reduce this compound in plants is essential. The use of regulatory elements such as selenium provides a practical solution for mitigating this issue.
The results of this study demonstrated that sodium selenite foliar application reduced nitrate accumulation, increased nitrate reductase enzyme activity, and enhanced selenium concentration in spinach. Nitrate reductase is a key enzyme in nitrogen metabolism, responsible for reducing nitrate to nitrite and facilitating its utilization in essential plant structures. Increased activity of this enzyme indicates improved nitrogen uptake and utilization, which can lead to better growth and higher yield.Therefore, foliar application of 1.5 mM sodium selenite in spinach is recommended to achieve maximum antioxidant compounds, increased selenium concentration, and minimal nitrate accumulation. This method not only improves the nutritional quality of agricultural products but also serves as a sustainable approach to reducing health risks associated with nitrate accumulation in vegetables. Furthermore, the application of selenium can enhance the plant’s defense mechanisms and increase its resistance to environmental stresses.
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