Systemin has been extensively studied since it was discovered and is described as a peptidic hormone in tomato plants and other . Jasmonic acid and systemin are proposed to act through a positive feed-back loop with jasmonic acid， playing synergistic roles in response to both wounding and insect attack. Despite its biological relevance， most studies regarding the function of systemin in defence have been studied via gene expression， which encodes the propeptide prosystemin that is later cleaved to systemin (SYS). Interestingly， hardly any studies have been based on quantification of the peptide.