Abstract
Phytohormones (plant growth regulators) can be applied as efficient elicitors to enhance the productivity of plant in vitro cultures, due to their significance in regulating the plant metabolism and strong influence on plant defense responses. In the present study, the effects of exogenous ethylene (ETY, applied in the form of ethephon as an ethylene-generating agent) and abscisic acid (ABA) on the synthesis of triterpenoids and steroids in Calendula officinalis hairy roots were investigated. ABA appeared to be an efficient elicitor of the biosynthesis of triterpenoid oleanolic acid (almost two-fold) and the release of its glycosides (saponins) to the culture medium (up to 6.6-fold). ETY had only a slight effect on triterpenoid metabolism; instead, it strongly influenced steroid metabolism, leading to profound modifications of the quantitative profiles of these compounds, particularly the ratio of stigmasterol to sitosterol. Both the applied phytohormones influenced the interplay between steroid and triterpenoid biosynthetic pathways, revealing the symptoms of their competition.
Highlights
Hairy root cultures (HRCs) are differentiated cultures of transformed roots which are induced by the infection with bacterium Rhizobium rhizogenes, known as Agrobacterium rhizogenes [1,2,3]
C. officinalis HRCs applied in the present study were shown to be capable of synthesizing one triterpenoid acid, i.e.,oleanolic acid, OA (3β-hydroxy-olean-12-en-28-oic a3coifd1)2, found both in the free form as well as its glycosides, which can be accumulated in the tissue and released to the surrounding medium
The influence of the ETY treatment on triterpenoid metabolism was rather slight; free OA accumulation in hairy root tissue was moderately increased at the concentration of 10 μM ETY and decreased at the concentration of 100 μM ETY.The
Summary
Hairy root cultures (HRCs) are differentiated cultures of transformed roots which are induced by the infection with bacterium Rhizobium rhizogenes, known as Agrobacterium rhizogenes [1,2,3]. The productivity of HRCs is not always sufficient for the economic viability, and several biotechnological strategies have been developed for its improvement This includes screening and selection of high-yield lines, optimization of culture media and culture conditions, replenishment of nutrients and precursor feeding, in situ product removal to overcome feedback inhibition, genetic engineering, as well as application of phytohormones and other elicitors [6,7]. Elicitation is currently one of the most practically feasible and most effective strategies for enhancing the production of phytochemicals in plant biotechnology [8,9,10,11,12] In this context, HRCs can serve as a suitable model for the investigation of the influence of different biotic and abiotic elicitors [13,14]
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