The selective induction of the phenylalanine ammonia-lyase pathway in the resistance response of wheat to the russian wheat aphid

Abstract

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is notorious for causing severe yield losses in many of the wheat producing areas of the world. The phenylpropanoid pathway is involved in many plant defence mechanisms. Phenylalanine ammonia-lyase (PAL) is a key enzyme leading to biosynthesis of phenolic acids, some of which are involved in plant defence mechanisms. The effect of RWA infestation on PAL activity and phenolic acid composition was studied in resistant (Tugela DN) and susceptible (Tugela) wheat cultivars. PAL activity was selectively induced in the infested resistant wheat. The increase in PAL activity was reflected in the selective increase in certain phenolic acid concentrations. The phenolic acids that were selectively induced in resistant wheat upon RWA infestation were identified using the authentic phenolic acids p-hydroxybenzoic acid, gallic acid, resorcylic acid, gentisic acid, caffeic acid, p-hydroxyphenylacetic acid, and ferulic acid. The induced levels of these phenolic acids corresponded to the peak PAL activities. It is evident that the phenylpropanoid pathway contributes to the resistance of wheat to the RWA.