The research team found that pipecolic acid, a small organic compound derived from lysine, initiates the process by inducing the accumulation of free radicals. Free radicals initiate a pathway that results in the accumulation of the signaling chemicals salicylic acid and glycerol-3-phosphate. Salicylic acid, glycerol-3-phosphate, and to a lesser extent, pipecolic acid then travel within the plant as part of the defense "preparedness" process. There, salicylic acid and glycerol-3-phosphate initiate additional pipecolic acid synthesis to continue this signaling pathway.
Pradeep Kachroo said that scientists knew the importance of pipecolic acid in systemic signaling, but did not understand how it related to the other known systemic chemical signals. Now they do not only know how pipecolic acid functions, but also how the chemical cooperates with other signals.
For details, read the UK news release.