All-trans-farnesol: a naturally occurring antitranspirant?

Lipid extracts from Sorghum sudanese Stapf (cv Piper) that had been subjected to different degrees of water stress contained increasing amounts of a sesquiterpenoid, other than abscisic acid, as the amount of stress increased and subsequent bioassay showed that this substance was capable of inducing stomatal closure. Infra-red, nuclear magnetic resonance and mass spectral analysis after final purification by preparative gas-liquid chromatography showed conclusively that this substance was identical to all-trans-farnesol. Various derivatives, homologues and isoprenologues of all-trans-farnesol were tested for their ability to close stomata. Only trans-nerolidol approached all-trans-farnesol in activity when applied to isolated epidermis of Commelina communis L. Stomatal closure was induced slightly faster and more completely in the presence of all-trans-farnesol than in the presence of ABA at a similar molar concentration.