Abstract
The aim of the study was the evaluation of the efficiency of selected abiotic elicitors, i.e., silver and cadmium ions, ultrasound, and UV-C irradiation, in the stimulation of triterpenoid biosynthesis, accumulation, and saponin secretion in Calendula officinalis hairy root cultures. Apart from the possible enhancement of triterpenoid production, the relationship between primary and secondary metabolism (represented respectively by sterols and pentacyclic triterpenes), modifications of the sterol compositional profile, and fluctuations in the total triterpenoid content were monitored in the performed experiments. The main phenomenon observed as a response to heavy metal treatment was the stimulation (up to 12-fold) of the secretion of saponins, accompanied by significant changes in sterol composition. Ultrasound stimulated the secretion of saponins (up to 11-fold); however, it exerted diverse influences on the triterpenoid content in hairy root tissue (stimulating or decreasing) depending on the duration of the exposure to the elicitor. UV-C radiation caused a slight increase in the content of both sterols and saponins in hairy root tissue, and stimulated saponin secretion up to 8.5-fold. The expected symptoms of the competition between the biosynthetic pathways of sterols and pentacyclic triterpenoids were less evident in reactions to abiotic stressors than those reported previously for biotic elicitors.
Highlights
Triterpenoids represent a large group of plant isoprenoids synthesized from the C30 precursor squalene, a linear hydrocarbon, which is oxidized to 2,3-oxidosqualene and rearranged by special enzymes, oxidosqualene cyclases, to various cyclic structures [1,2]
We studied the effect of selected abiotic factors, i.e., silver and cadmium ions, ultrasound, and Ultraviolet radiation (UV)-C irradiation, on triterpenoid productivity in two C. officinalis hairy root lines differing in origin from initial explant
The main sterols identified by GC-MS in C. officinalis hairy roots were: campesterol [(24R)-ergost5-en-3β-ol], cholesterol [cholest-5-en-3β-ol], isofucosterol [stigmasta-5,24(28)-dien- 3-ol], stigmasterol
Summary
Triterpenoids represent a large group of plant isoprenoids synthesized from the C30 precursor squalene, a linear hydrocarbon, which is oxidized to 2,3-oxidosqualene and rearranged by special enzymes, oxidosqualene cyclases, to various cyclic structures [1,2]. Two main groups can be distinguished among these derived structures: steroids, i.e., tetracyclic compounds based on the perhydro-1,2-cyclopentano-phenanthrene moiety, and pentacyclic triterpenoids possessing a 5-ring carbon skeleton in various arrangements. Steroids contain a characteristic class of compounds with a hydroxyl group at C-3 called sterols. Plant sterols can exist in plants in a basic free form, and as esters with fatty or phenolic acids, or as glycosides and acylated steryl glycosides [3,4]. Pentacyclic triterpenoids can be classified according to their type of skeleton into oleananes, ursanes, lupanes, taraxasteranes, etc. They can exist in plants in free or bound forms, i.e., as esters or glycosides, referred to as saponins
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