The Effect of Drought Stress on Some Morphological, Phytochemical, and Biochemical Characteristics of the Medicinal Plant Field Sowthistle (Sonchus arvensis L.)

Field Sowthistle (Sonchus arvensis L.) is a plant with high potential medicinal and nutritional values, the medicinal properties of this plant are due to the presence of important phytochemical compounds, especially phenols, and flavonoids. Drought is an important abiotic stress and the most limiting factor for plant growth and production. S. arvensis has valuable secondary metabolites, hence investigation on the responses of this plant against drought stress is of great importance. The purpose of this research was to study the effect of drought stress on morphological characteristics and some phytochemical and biochemical parameters in S. arvensis.

To investigate the effect of drought stress on the morphological, phytochemical, and biochemical characteristics of Field Sowthistle, a pot experiment was carried out as a completely randomized design in three replications. The treatment of drought stress included four levels of 100% (non-stress), 75%, 50%, and 25% of field capacity. The morphological traits studied were shoot and root fresh weight, shoot and root dry weight, plant height, and root length. Also, phytochemical traits include photosynthetic pigments, relative water content, total phenol, total flavonoid, antioxidant capacity with two DPPH and FRAP methods, proline and soluble sugar, and biochemical traits such as activity of antioxidant enzymes catalase, superoxide dismutase, glutathione Peroxidase, ascorbate peroxidase, and total protein were also measured in middle and lower leaves.

The results showed that drought stress had a significant effect on the growth components, the relative content of leaf water, proline, soluble sugar, chlorophyll a and b and total chlorophyll, carotenoid, total phenol, total flavonoid, antioxidant activity of catalase, superoxide dismutase, ascorbate peroxidase, guaiacol peroxidase and inhibition of DPPH radical activity and iron reducing power (FRAP). With the decrease in soil water content, plant height, fresh and dry weight of shoots and roots, relative water content, chlorophyll a and total chlorophyll decrease, and in contrast to root length, chlorophyll b, carotenoid, proline, soluble sugar, total protein, phenol and Total flavonoid, antioxidant enzymes, inhibition of DPPH radical activity and iron reducing power (FRAP) increased. Also, some traits were investigated in the middle and lower leaves, and there was a difference between the above traits between the middle and lower leaves, and the middle leaves contained more of the examined traits.

The results of the present study indicated that drought stress decreases morphological traits except for root length. Also, a higher amount of phytochemical traits were observed in the middle leaves compared to the lower leaves. In general, drought stress caused an increase in the biochemical and phytochemical traits, except for the relative water content, chlorophyll a, and total chlorophyll.