Phytochemical investigation and reproductive capacity of the Bulgarian endemic plant species Marrubium friwaldskyanum Boiss. (Lamiaceae)

Authors: ZHELJAZKOV, VALTCHO - Oregon State University; SEMERDJIEVA, IVANKA - Agricultural University Of Bulgaria; STEVENS, JAN - Oregon State University; WU, WENBIN - Oregon State University; Cantrell, Charles; YANKOVA-TSVETKOVA, ELINA - Bulgarian Academy Of Sciences; KOLEVA-VALKOVA, LYUBKA - Agricultural University Of Bulgaria; STOYANOVA, ALBENA - Agricultural University Of Bulgaria; ASTATKIE, TESS - Dalhousie University

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/24/2021
Publication Date: 12/30/2021
Citation: Zheljazkov, V.D., Semerdjieva, I.B., Stevens, J.F., Wu, W., Cantrell, C.L., Yankova-Tsvetkova, E., Koleva-Valkova, L.H., Stoyanova, A., Astatkie, T. 2021. Phytochemical investigation and reproductive capacity of the Bulgarian endemic plant species Marrubium friwaldskyanum Boiss. (Lamiaceae). Journal of Agricultural and Food Chemistry. https://doi.org/10.3390/plants11010114.
DOI: https://doi.org/10.3390/plants11010114

Interpretive Summary: Marrubium friwaldskyanum Boiss (Lamiaceae) is a Bulgarian endemic species. Endemic plants represent untapped resources with potential as a source of natural products with new chemical constituents or profiles. This is the first report on the endemic species M. friwaldskyanum phytochemistry, embryology, and surface analyses of nutlet (seed) and pollen structure and seed viability. The essential oil (EO) composition of M. friwaldskyanum was dissimilar to that of other Marrubium species EO profile reported in the literature. Overall, the phytochemistry and some of the miscroscopic analyses distinguished this endemic species from other species in Marrubium. Marrubium friwaldskyanum seems promising to be developed as a new cash crop. A similar species, M. vulgare (horehound), is among the top selling herbal supplements in the U.S.

Technical Abstract: Marrubium friwaldskyanum Boiss (Lamiaceae) is a Bulgarian endemic species. Endemic plants represent untapped resources with potential as a source of natural products with new chemical constituents or profiles. This is the first report on the endemic species M. friwaldskyanum phytochemistry, embryology, and surface analyses of nutlet (seed) and pollen structure and seed viability. Overall, the essential oil (EO) composition of M. friwaldskyanum was dissimilar to that of other Marrubium species EO profile reported in the literature. The main EO constituents of M. friwaldskyanum were caryophyllene, germacrene D, bicyclogermacrene, and caryophyllene oxide. The effect of harvest stage was significant only on copaene, caryophyllene, caryophyllene oxide, and muurolol. The concentration of copaene (1.26-1.83% range of the total oil), caryophyllene (31-41%), caryophyllene oxide (6.4-11.8%), and muurolol (1.3-2.8%) were the highest at 2-3 pair of leaves or before flowering and lower at flowering. Harvest stage did not significantly affect the concentrations of the other six identified EO compounds bourbonene (1.1%),'humulene (2.8%), germacrene D (23.3%), bicyclogermacrene (2.85%), cadinene (1.1%), and spathulenol (2.8%). In a separate experiment, grinding of the biomass prior to EO extraction had significant effect only on the concentrations of limonene (0.24-3.3% of the total oil) and bicyclogermacrene (3.6-9.1%). Grinding in water or without water, maceration, and addition of Tween 20 had rather small effects on EO profile. The identified EO constituents and their mean concentrations in this experiment were caryophyllene (25.4%), germacrene D (17.6%), caryophyllene oxide (9.1%), spathulenol (6.5%), muurolol (5.0%), carvacrol (3.9%), copaene (2.5%), bourbonene (2.5%), cadinene (2.4%), humulene (1.8%), and farnesene (1.3%). Embryological studies observed anther and the development of the male gametophyte and also ovule and development of the female gametophyte of M. friwaldskyanum. Furthermore, pollen and seed viability assays were conducted. Mass spectrometry-based metabolomics analysis of an extract of the aboveground shoots revealed the presence of 48 natural products which were identified as flavonoids, phenolic acids, and (tri)terpenoids by comparison with a natural products library containing 500 authentic standards. In addition, morphological analyses of leaves, stems, calyx, and corolla surfaces were conducted using scanning electron microscopy (SEM). Overall, the phytochemistry and some of the miscroscopic analyses distinguished this endemic species from other species in Marrubium. Marrubium friwaldskyanum seems promising to be developed as a new cash crop. A similar species, M. vulgare (horehound), is among the top selling herbal supplements in the U.S.