Chemical Composition and Phytotoxic Activity of Essential Oil from Senecio erucifolius

Translated from Khimiya Prirodnykh Soedinenii, No. 3, May–June, 2021, pp. 492–493.

Senecio erucifolius L. (Asteraceae) is a perennial plant with a rhizomatic thermophilic habit that is distributed in parts of Asia, Europe, and the Mediterranean [1, 2]. Many species of the genus Senecio are used in traditional medicine in Asia and Africa [3]. The genus Senecio numbers ~1100 species worldwide that are well known as rich sources of pyrrolizidine alkaloids [4]. Previous phytochemical investigations found pyrrolizidine alkaloids, cyclohexanone derivatives, and flavonoids in S. argunensis, which was considered a subspecies of S. erucifolius [5, 6]. Also, three new compounds including semiquinol butyl 2-(1-hydroxy-4-oxocyclohexa-2,5-dienyl)acetate, the semiquinol jacaranone, and methyl 2-(4-hydroxyphenyl)acetate were isolated from S. erucifolius [3]. However, the chemical composition and phytotoxic activity of S. erucifolius essential oil were not investigated.

The aerial part of S. erucifolius was collected in June 2018 in Shawan District, Xinjiang Province, China (43.9680° N, 85.8763° E; 1146 m elevation), during flowering. A voucher specimen (serial No. XJBI 201825706) is deposited in the herbarium of Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences. Essential oil was extracted by traditional steam distillation for 4 h using fresh plant (200 g). Then, the essential oil was dried over anhydrous Na2SO4 and stored in a closed brown vial at 4°C. The yield of yellow essential oil was 0.18%.

The chemical composition of the essential oil was analyzed using a 7890A-5975C GC-MS system equipped with a DB-5ms column (5%-phenyl-methylpolysiloxane; 30 m × 0.25 mm; 0.25 μm film thickness) and a flame-ionization detector [7]. The relative contents of separate compounds were calculated from GC peak areas without correction coefficients. Constituents were identified by comparing their mass spectra and retention indices (RI, calculated by linear interpolation relative to the retention times of a standard mixture of C7-C40n-alkanes under the same GC-MS operating conditions) with the NIST14 database library and our own libraries [8, 9].

A total of 37 compounds were identified, which was 85.7% of the total essential-oil mass. They were classified as sesquiterpene hydrocarbons (32.7%), non-terpene O-containing compounds (29.0%), hydrocarbons (14.4%), monoterpenes (6.6%), and oxygenated sesquiterpenes (2.1%). The dominant constituents were dibutyl phthalate (16.2%), isoledene (7.7%), β-cis-ocimene (5.5%), butylcyclopentane (4.9%), and germacrene D (4.8%) (Table 1).

Table 1. Chemical Composition of Essential Oil from S. erucifolius

The phytotoxic activity of the essential oil was evaluated against three weeds, i.e., Medicago sativa L., Urtica cannabina L., and Amaranthus retroflexus L. [7]. The essential oil was first dissolved in Me2CO (final concentration 0.5%), diluted with distilled H2O to produce solutions of concentrations 0, 0.125, 0.25, 0.5, 1, 2, and 4 mg/mL (Me2CO in a preliminary experiment at these concentrations did not significantly affect the development of sprouts of the test plants). Six repetitions of the phytotoxicity biotest were performed (n = 60). In general, the essential oil at low concentrations stimulated growth of sprouts of the treated species; at high concentrations, suppressed it.

The length of roots of M. sativa, U. cannabina, and A. retroflexus increase by 21.00, 10.46, and 2.53%, respectively, after treatment with oil at the lowest concentration (0.125 mg/mL) and decreased by 9.36, 23.00, and 19.53% after treatment at the highest concentration (4 mg/mL). The lengthening of the runners was analogous to the essential oil but to a lesser extent (Table 2).

Table 2. Phytotoxic Activity of Essential Oil from S. erucifolius

Length of roots and runners expressed as average ± SE (n = 60); statistically significant difference (p < 0.05) shown by different letters.

Dibutyl phthalate, the dominant constituent of S. erucifolius essential oil, is widely used as a plasticizer. It was often detected in plants such as Atriplex cana and in microorganisms, indicating that it may be biosynthesized [10–13]. Furthermore, nanoplastics can accumulate in plants depending on their surface charge. This could have direct impacts for the environment and agricultural security [14]. Thus, we came to the conclusion that dibutyl phthalate in the essential oil could have come from environmental contamination or biosynthesis by S. erucifolius itself.

The work was financially supported by the Second Tibetan Plateau Scientific Expedition and Research (STEP) (2019QZKK0502) in collaboration with the Program of Tian-Shan Scientists of Shandong, China (ts201712071).