Investigating the role of brassinolide in tolerance to lead toxicity on growth and physiological traits of pinto beans

Background and objectives:
Heavy metal pollution is becoming a serious problem for agricultural lands and a great threat to the sustainability of agricultural ecosystems. Lead is one of the most dangerous heavy metals, which is the second heavy metal after arsenic in terms of toxicity and occurrence. One of the important aspects of tolerance of non-living stresses including heavy metals in plants is the role of plant growth regulators. Among these growth regulators, we can mention brassinosteroid, which plays an important role in inducing the reaction of plants to many abiotic stresses such as heavy metals. As a messenger molecule, this compound increases the activity of antioxidant enzymes and reduces the production of reactive oxygen species. In the production of the leguminous family, the toxicity caused by heavy metals has a significant effect. Therefore, the present research is aimed at investigating the effect of the heavy metal lead and the moderating effect of brassinolide.
Materials and methods:
This experiment was conducted in the spring and summer of 1400 in a potted form in a greenhouse located in Ray City in order to investigate the role of brassinolide application in reducing the toxicity caused by lead heavy metal stress in the pinto bean plant variety. This research was conducted in the form of a completely randomized design with 6 treatments and 4 replications. The treatments were 1) control (no application of lead and brassinolide) (T1). 2) lead stress (application of 200 mg/kg of soil from a source of lead nitrate) (T2). 3) lead stress + seed treatment with brassinolide. Concentration of 0.1 mg/liter for 12 hours (T3). 4) Lead stress + seed treatment with brassinolide with a concentration of 0.2 mg/liter for 12 hours (T4). 5) Lead stress + spraying Brassinolide with a concentration of 0.1 mg/liter from the 4-leaf stage during 3 stages with an interval of 7 days (T5). During 3 stages with an interval of 7 days (T6).
Results:
The results of this research showed that the vegetative traits all decreased due to the use of lead and the toxicity of this heavy metal, but biomarkers and antioxidant enzymes increased along with root lead. This method increased the resistance of pinto beans to lead stress. The results of the mean comparisons showed that the highest seed yield with an average of 18.31 gr/plant was obtained from the control treatment (no use of lead and brassinolide) and the lowest amount with an average of 8.22 grams per plant was obtained from the treatment of lead toxicity with an amount of 200 ml g/kg and lack of brassinolide consumption were found to moderate the effect of lead. Also, among the treatments in which brassinolide was used as a compound preventing the harmful effects of the heavy metal lead, the highest amount with an average of 13.84 grams per plant was related to the use of 0.2 mg/liter as a foliar spray, which indicates The superiority of using brassinolide as a foliar spray is compared to other methods and consumption amounts.
Conclusion:
These results showed that seed pretreatment and foliar spraying with brassinolide can be used as a useful method to tolerate lead stress in beans by reducing lead absorption, increasing the activity of antioxidant enzymes and improving the greenness index and water condition of the plant.