Reduction of lead toxicity effects and enhancing the glutathione reservoir in green beans through spraying sulfur and serine and glutamine amino acids.

Acid rain is one of the influential environmental factors in transport of heavy metals, including lead from the atmosphere to the surface of the earth and growing plants. Such situation can not only damage the growing plants but can also toxify the food chain, and endanger human life. In order to reduce stress damage due to lead, on green bean plant, the effect of spraying the plants by sulfur, also amino acids including serine and glutamine, was evaluated. A factorial experiment based on randomized complete block design with three replications was carried out using the green bean Sunray cultivar in 2020. Treatments include foliar application of lead at two levels (0.0 and 1 mmol) as lead acetate, foliar application of liquid sulfur at two levels (0.0 and 2 per thousand), and foliar application of amino acids at four levels (0.0, serine at 200 mg/L, glutamine at 200 mg/L, and co-application of serine and glutamine at the same concentrations) at pre-flowering stage. The results showed that leaf foliar uptake of most of the employed treatments resulted in reduction of leaf area index, leaf, stem and pods dry weight, stem diameter and height, pod yield, photosynthetic pigments such as chlorophyll a, chlorophyll b, and carotenoids, and relative leaf water content. However, grain protein content, hydrogen peroxide, and glutathione antioxidant activity significantly increased. Spraying of sulfur solution and serine and glutamine were effective in reducing the negative effects of lead stress, as it reduced the amount of hydrogen peroxide and grain protein and increased the reservoir of glutathione. These treatments also, compared to the pure lead treatment, significantly reduced lead accumulation in the pod, as the edible organ of green beans. This study results showed that foliar application of sulfur along with amino acids serine and glutamine reduced the lead toxicity effects through improving the physiological functions, and thus can increase the final yield and consequently human access to healthier food (Fig. 1). Fig. 1 Graphical abstract.