Flavonoids (antioxidants systems) in higher plants and their response to stresses

Abstract

Flavonoids are a diverse group of secondary metabolites with a wide range of roles in mechanisms relating to UV protection, insect attraction, pathogen defense, symbiosis, variation of flower color, male fertility, pollination, allelopathy and auxin transport. Except bryophytes and pteridophytes, flavonoids are found only in higher plants. Flavonoids act as an antioxidative agent and scavenge reactive oxygen species (ROS), which are generated in plants during biotic and abiotic stresses. The ROS prevention by flavonoids is achieved through the inhibition of ROS-generating enzymes, the recycling of other antioxidants and the chelation of transition metal ions. Flavonoids are considered to be a secondary antioxidant system since they complement the function of other ROS scavenging systems when the reduction in the activities of antioxidant enzymes. This chapter describes the role of flavonoids in response to various stresses in higher plants.