Document Type : Original research article

Authors

• Mostafa Sarani ¹
• Maryam Allahdou ²
• Leila Mehravaran ²
• Halimeh Piri ³

¹ M.Sc Graduated in Agricultural Biotechnology, University of Zabol, Zabol, Iran

² Department of Plant Breeding and Biotechnology, University of Zabol, Zabol, Iran

³ Department of Irrigation, University of Zabol, Zabol, Iran

Abstract

Drought stress is the primary constraint on crop and medicinal plant yields in arid and semi-arid regions. Milk thistle is a medicinal plant with antioxidant secondary metabolites (flavonolignans). The effect of drought stress was evaluated in this study at three growth stages (6, 13, and 20 weeks after planting) using four different levels of irrigation (100, 75, 50%, and 25% of water requirement, respectively, as non-stress, mild stress, moderate stress, and severe stress). The experiment was conducted in a greenhouse located in Shandol village, Hirmand city, Iran, as a factorial experiment with a completely randomized design. The following agronomic and physiological characteristics were determined: fresh weight, dry weight, photosynthetic pigments, proline, carbohydrates, malondialdehyde, relative water content, and ion leakage. The results indicated that the effect of various irrigation levels, harvest time, and their interaction were significant for the majority of traits, except for the relative water content and ion leakage traits, indicating that these traits react differently at various growth stages. Fresh weight, dry weight, photosynthetic pigment content, and relative water content all decreased under drought stress conditions, to the point where the lowest amount was observed under severe drought stress (25% of water requirement). Drought stress results in thylakoid protein hydrolysis, chlorophyll a and chlorophyll b reduction, and pigment and photosynthetic structure loss. With increasing stress intensity, the concentrations of proline, carbohydrates, malondialdehyde, and ion leakage increased. As a result, the highest amount was discovered under severe drought stress conditions. As a result, this increase indicates that the plant is suffering from oxidative stress as a result of the drought. Proline content increased proportionately to the severity of the stress, reaching its maximum value under severe drought stress (25% water requirement). Thus, under drought stress conditions, milk thistle responds to oxidative stress by increasing the accumulation of this osmolyte

Highlights

• The study examines how drought stress affects milk thistle across three growth stages.
• The paper shows that drought stress reduces milk thistle biomass and photosynthetic pigment and increases proline and carbohydrates, indicating oxidative stress.
• The paper shows that milk thistle plant physiological traits vary significantly with irrigation level, harvest time, and their interaction, suggesting that the plant adapts to drought stress differently at different growth stages. 

Keywords

• Malondialdehyde
• Oxidative stress
• Photosynthetic pigments
• Water requirement