The Effect of Using Salicylic Acid and Sodium Nitroprusside on the Physiological Characteristics of Henna (Lowsonia inermis L.) under Drought Stress

IntroductionHenna (Lawsonia inermis L.) is a perennial, dicotyledonous plant native to North Africa and Southeast Asia. This plant is cultivated in tropical regions as an ornamental species and for its dye production (Singh, Luqman, & Mathur, 2015). Drought stress directly affects a range of physiobiochemical and phytochemical processes, as well as molecular responses (Farooq, Wahid, Kobayashi, Fujita, & Basra, 2009; Rady, Belal, Gadallah, & Semida, 2020). Salicylic acid is a phenol-based phytohormone that regulates vital physiological activities within the plant, including water uptake, ion transport, transpiration, and photosynthesis (Klessig, Choi, & Dempsey, 2018). Sodium nitroprusside is a nitric oxide-releasing compound (Farouk & Al-Huqail, 2020). Nitric oxide inhibits free radicals by inducing gene expression and enhancing the activity of antioxidant enzymes, thereby protecting cells from damage caused by abiotic stresses (Ahmad et al., 2016).Materials and MethodsThis experiment was conducted in 2021 on a farm located in Qaleganj City, Kerman Province. The climate of Qaleganj is classified as semi-desert according to the dry amber method. The characteristics of the soil at the test site are detailed in Table 1. The experiment was carried out in the form of split plots based on a randomized complete block design with four replications. The main factor included three levels of irrigation (50%, 75%, and 95% of crop capacity), while the secondary factor involved foliar spraying with growth regulators (control, salicylic acid, sodium nitroprusside, and a combination of salicylic acid and sodium nitroprusside). The seeds of the henna plant (Lawsonia inermis L.) were obtained from the Faculty of Agriculture at Bahonar University, Kerman, Iran. The planting date for the henna plant was April 1, and the harvesting date was November 5.Results and DiscussionThe results showed that drought stress caused a decrease in traits such as plant height, leaf area index, and yield. Additionally, drought stress increased traits such as malondialdehyde concentration, ascorbate peroxidase enzyme activity, catalase enzyme activity, and phenylalanine ammonialyase enzyme activity. The application of the combination of salicylic acid and sodium nitroprusside enhanced the leaf surface index, ascorbate peroxidase enzyme activity, catalase enzyme activity, and phenylalanine ammonialyase enzyme activity. The highest seed yield from the treatment with the combination of salicylic acid and sodium nitroprusside was 3546.66 kg.ha-1 under irrigation conditions of 95% of crop capacity, while the lowest seed yield, from the treatment without growth regulator application, was 2243.33 kg ha-1 under 50% crop capacity conditions.ConclusionWhen faced with drought stress, the henna plant employs osmotic regulation mechanisms by increasing the accumulation of proline, thereby tolerating water deficit conditions to some extent. Spraying the combination of salicylic acid and sodium nitroprusside resulted in an increase in antioxidant enzymes, leaf surface index, and leaf density per hectare, helping to mitigate the destructive effects of stress. Based on the results of this research, it is recommended to use a salicylic acid and sodium nitroprusside solution under drought stress conditions to maintain performance in henna plants.