Induction of Phenylalanine ammonia-lyase and lipoxtgenase in cotton seedlings by mechanical wounding and aphid infestation*

Abstract

Abstract It has been suggested that infestation of plants causes increases in the activities of phenylalanine ammonia-lyase (PAL) and lipowygenase (LOX), key enzymes in the phenolic compounds synthesis pathway and the octadecanoid pathway, respectively. The purpose of this work is to investigate whether he infestation of cotton aphid (Aphis gossypii) and mechanical wound can cause the induction of PAL and LOX activities in cotton seedlings, and whether the induction occurs in healthy seedlings growing nearby the attacked ones. The specific activities of PAL and LOX were measured using spectrophotometric method after aphid infestation and mechanical wounding. Result indicated that PAL activity and LOX activity were greatly induced by mechanical wounding and aphid infestation in cotton seedlings. The induction of PAL and LOX occured not only in wounded and infested seedlings but also in intact healthy seedlings growing nearby. After exposed to the aphid infestation-induced volatiles, the specific activity of PAL in cotton seedlings increased by 6% at 24 h, 80% at 48 h, 235% at 72 h compared to the control, and the specific activity of LOX increased by 18% at 24 h, 34% at 48 h, 24% at 72 h, 200% at 48 h, 164% at 72 h, respectively and the specific activity of LOX increased by 28% at 24 h, 37% at 48 h, 8% at 72 h, respectively. It suggests that the included volatiles are involved in plant-plant communication as airborne transferred signals.