Polyphenol oxidase participates in the response of plants to wounding and herbivore attack, mediated by the octadecanoid wound-signalling pathway. Chloroplast polyphenol oxidase is a 64 kDa nuclear-encoded protein that is targeted to the thylakoid lumen. It was found that polyphenol oxidase is one of the most strongly phosphorylated protein in thylakoid lumen although the role of this protein modification is not known (Sokolenko et al., 1995, FEBS Lett. 371, 176 – 180, Koussevitzky et al., 2004, Planta 219, 412 - 419).