Saponarin, a Di-glycosyl Flavone from Barley (Hordeum vulgare L.): An Effective Compound for Plant Defense and Therapeutic Application

Abstract

Saponarin (SA) is a major di-C-glycosyl-O-glycosyl flavone, which is predominantly accumulated in the young green leaves of barley (Hordeum vulgare L.), with numerous biological functions in plants, such as protection against environmental stresses. Generally, SA synthesis and its localization in the mesophyll vacuole or leaf epidermis are largely stimulated in response to biotic and abiotic stresses to participate in a plant's defense response. In addition, SA is also credited for its pharmacological properties, such as the regulation of signaling pathways associated with antioxidant and anti-inflammatory responses. In recent years, many researchers have shown the potential of SA to treat oxidative and inflammatory disorders, such as in protection against liver diseases, and reducing blood glucose, along with antiobesity effects. This review aims to highlight natural variations of SA in plants, biosynthesis pathway, and SA's role in response to environmental stress and implications in various therapeutic applications. In addition, we also discuss the challenges and knowledge gaps concerning SA use and commercialization.

Figure 1

Chemical structure of saponarin (C₂₇H₃₀O₁₅).

Figure 2

Schematic representation of saponarin biosynthesis pathway in barley. The malonyl-CoA and 4-coumaroyl-CoA are condensed to form naringenin via CHS, followed by a ring closure reaction by CHI. The further successive step involved in the formation of isovitexin flavone remains unelucidated up to now. OGT catalyzes competing reactions to generate saponarin by adding another sugar substituent to the 7-O position of the isovitexin backbone. Enzyme abbreviations: CHS, chalcone synthase; CHI, chalcone isomerase; CGT, DIOX, dioxygenase; UDP-Glc-dependent C-glucosyltransferase; FNS, flavone synthase (hypothetical), OGT, UDP-Glc:Flavone-7-O-glycosyltransferase.

Figure 3

Effect of environmental factors on saponarin accumulation in young barley leaves.

Figure 4

Screening and antioxidant roles of saponarin in young barley leaves under UV–B radiation.

Figure 5

Therapeutic potential of saponarin against inflammatory disorders.