Detection and preliminary identification of endogenous antitranspirants in water-stressed Sorghum plants

Sorghum plants that had been subjected to different degrees of water stress were examined for the occurrence of endogenous compounds capable of inducing stomatal closure, i.e. "antitranspirants". Acidic extracts contained increased amounts of abscisic acid (ABA) as the amount of stress increased, but another highly active compound easily distinguished from ABA also accumulated. This compound, also found in neutral extracts, was probably all trans-farnesol, an isoprenoid alcohol which, like ABA, is a sesquiterpenoid. Highly dilute solutions of "commercial" farnesol induced stomatal closure when applied to isolated epidermis of Commelina.