Red clover (Trifolium pratenseL.) isoflavones: root phenolic compounds affected by biotic and abiotic stress factors

Abstract

Phenolic compounds have recently received considerable attention for their ability to protect plant and human cells from oxidative stress-induced damage. Red clover (Trifolium pratense L.) is a rich source of isoflavonoids with multiple potential protective functions. The aim of this study was to identify and characterise phenolic compounds in red clover roots by high-performance liquid chromatography and mass spectrometry and to study the effects of stress factors and growth stage on root phenolics. A total of 28 phenolic compounds were tentatively identified in red clover roots. The most abundant phenolics in pot-grown roots were formononetin glycoside malonate (G-M) (1.51-4.26 mg g(-1)), formononetin (2.21-3.57 mg g(-1)) and biochanin A (1.73-2.17 mg g(-1)), whereas field-grown roots were rich in formononetin-G-M (3.90-4.27 mg g(-1)), maackiain-G-M (2.35-3.02 mg g(-1)) and pseudobaptigenin-G-M (1.80-2.58 mg g(-1)). Concentrations were affected by the growth stage. Ozone exposure slightly affected the total phenolic content in roots and also had minor effects on individual compounds. Elevated ozone, cultivation regime and growth stage affected the levels of phenolics in red clover roots, suggesting sensitivity of root phenolics to biotic and abiotic stress conditions. The high levels of phenolics found in roots even in late autumn may be utilised in many applications.