Environmental stress effect on the phytochemistry and antioxidant activity of a South African bulbous geophyte, Gethyllis multifolia L. Bolus

Abstract

Gethyllis multifolia is a South African bulbous geophyte with medicinal properties and on which very limited research has been conducted. This research investigated the effect of drought and shade, which are experienced in the natural habitat, on the antioxidant properties, as well as the isolation of natural compounds from certain plant parts. The total polyphenol, flavonol/flavone and flavanone contents, oxygen radical absorbance capacity (ORAC), ferric reducing antioxidant power (FRAP) and radical cation scavenging ability (ABTS) were measured in the leaves, bulbs and roots (dry weight) of G. multifolia under photo- and drought stress. A significantly higher total polyphenol content was observed in the roots under the photo- and drought stresses when compared to the control. When all the plant parts were compared, the highest total polyphenol content was observed in the drought-stressed roots of G. multifolia. An increased antioxidant capacity was observed in the root system of G. multifolia where the FRAP, ORAC and ABTS were found to be significantly higher during drought stress when compared to the control. Phytochemical investigation of the leaves, bulbs and roots of G. multifolia revealed the presence of tannins, flavonoids, phenolics, saponins, glycosides (phenolic and terpenoid) as well as essential oils, while the test for alkaloids was negative. Further in -depth studies on the roots of G. multifolia led to the isolation of three known flavonoids, of which one was also isolated as its endogenously acetylated derivative. Their structures were elucidated by chemical and spectroscopic methods as 2,3-dihydro-7-hydroxy-2-phenyl-4H-1-benzopyran-4-one (1), (1-[2.4-dihydroxyphenyl]-3-phenylpropan-1-one) (2), 2,3-dihydro-5,7-dihydroxy-2-phenyl-4H-1-benzopyran-4-one or pinocembrin (3) and 5,7-diacetoxy-2,3-dihydro-2-phenyl-4H-1-benzopyran-4-one (4). This investigation indicated how environmental conditions can be manipulated to enhance the antioxidant properties of certain plant parts for future cultivation of this species and the isolation of the four natural compounds elucidated its medicinal potential and created a platform for future in vivo research.