Castor bean,crude extract and ricin are potential sources of the “ricin letter” events,which have posed a great threat on public security worldwide.Investigations on tracing the geographic origins of castor beans are of urgent need in case of accidental food ingestion,environmental exposure and deliberate poisoning.Here,based on a thorough optimization of section preparation,matrix application and several key parameters,a novel,sensitive and convenient matrix assisted laser desorption ionization-mass spectrometry imaging(MALDI-MSI) method was firstly established for three endogenous defensive Ricinus communis biomarkers(RCB) with high abundance and low toxicity.Using the mature castor beans obtained from representative geographic origins,Shanxi province in North China and Sichuan province in South China,the abundance and spatial,longitudinal distributions of three RCBs in the castor bean sections were elucidated.Results showed that the RCBs were mainly distributed in the endosperm and embryo of the mature seeds,which exerted distinct abundance difference between Shanxis and Sichuans.Furthermore,the reconstructed 3D MSI model based on the longitudinal visualization in half of a Shanxis seed revealed different abundances of RCBs in main organs of castor beans,consistent with the 2D MSI results.Moreover,the three RCBs all belonged to the component of the highest contribution degree in the non targeted data mining analysis.It is suggested that a whole set of RCBs 1-3 should be integratedly regarded as the traceable biomarkers for different geographical location.The low cytotoxic effect of RCBs assured a safe and reliable alternative way for retrospective analysis.This new MSI strategy exhibits its high sensitivity and favorable applicability in deep insight to unravel the role of defensive peptides biomarkers in intoxication identification,and could timely respond to food and environment sourced hazard emergencies.