Uncovering Organosulfur Natural Products in the 'Shy-Plant' Mimosa pudica via Direct Analysis in Real Time Mass Spectrometry: Volatiles Emission from Touch Sensitive Roots

Mimosa pudica L. (Mimosaceae) is a small shrub endemic to South America, now pantropically distributed. M. pudica displays the properties of seismonasty where the leaves fold and stems droop in response to both touch, as well as nyctinasty, a type of circadian rhythm. It was previously reported that the principal component of the odor that is produced when M. pudica is uprooted is caused by CS 2 and COS, both of which were detected by GC-MS. The present study has found that the roots emit a foul odor in response to direct root stimulation. Further, neither CS2 nor COS were observed when plant volatiles were adsorbed onto a SPME fiber and analyzed by DART-TOF-MS. Detected in the root headspace were a mixture organosulfur compounds including S-propyl-1-propanethiosulfinate, propane sulfenic acid, 2,4,6-triethyl-1,3,5-trithiane, 2-mercaptoaniline and the antipsychotic derivative phenothiazine. GC-MS analysis of SPME fibers exposed to M. pudica root volatiles showed the presence of CS2. It is demonstrated here that DART-TOF-MS is a useful tool in the study of reactive and fleeting organosulfur species that are too heat labile to be observed by GC-MS. A hypothesis that explains the appearance of CS2 is that organosulfur compounds are heat labile and undergo secondary reactions when exposed to high GC injection port temperatures.