Influence of different cytokinins on the phenolic acids and antioxidant activity of two Brachystelma species

Abstract

The genus Brachystelma morphologically ranges from slender climbers to geophytes that mainly occur in Australia, Southeast Asia and sub-Saharan Africa. These species are well-known for their nutrition and medicinal values. The current study evaluated the effect of cytokinins (CKs) on the phenolic acid content and antioxidant activity of two in vitro-regenerated Brachystelma species. We quantified the phenolic acids (using Ultra-high performance liquid chromatography-tandem mass spectrometry, UHPLC-MS/MS) and antioxidant (Oxygen radical absorbance capacity, ORAC) potential of two (B. pulchellum and B. pygmaeum) species that were successfully micropropagated, with the use of three cytokinins (CKs): benzyladenine (BA), isopentenyladenine (iP) and meta-topolin riboside (mTR). The presence of CKs strongly influenced the concentrations of the 11 phenolic acids (consisting\xa0of seven hydroxybenzoic acids and four hydroxycinnamic acids) and ORAC of the in vitro-regenerated B. pulchellum and B. pygmaeum. Generally, the levels of hydroxycinnamic acids were higher than the hydroxybenzoic acids in both Brachystelma species. Ferulic (9–55\xa0µg/g DW) and sinapic (14–97\xa0µg/g DW) acids were the major phenolic acids in the micro-propagated plants. In both Brachystelma species, the majority of the CK-regenerated plants had higher ORAC relative to the control. The best antioxidant activity (>\u200970\xa0μmol/g Trolox equivalents, TE) was obtained from 25\xa0μM iP and mTR treatments for B. pulchellum and B. pygmaeum, respectively. Overall, the current study demonstrated the ability of CKs to serve as a suitable tool for the production of valuable therapeutic chemicals in the two Brachystelma species. Application of cytokinins (CKs) had a significant effect on the quality and quantity of phenolic acids in in vitro cultured Brachystelma pulchellum and B. pygmaeum. We observed the accumulation of 11 phenolic acids (7 hydroxybenzoic acids and 4 hydroxycinnanmic acids) at varying concentrations. Ferulic and sinapic acids were the most abundant phenolic acids in the in vitro-regenerants and increased in response to\xa0the CK treatments. In addition, the presence of CKs successfully enhanced the ORAC of the in vitro-regenerated B. pulchellum.