Ultrahistochemical Detection of Epoxides in Plant Cuticular Membranes

Abstract

Ultrathin sections of the cuticular membranes of several plant species show a deposit of silver granules after reaction with an acidic solution of iodide ions followed by silver proteinate solution. Depolymerization analysis of the cutins from 20 species in which the staining reaction was studied indicated that expoxide groups were the reactive components. Experiments with isolated cuticular membrane preparations and with pure cutin monomers supported this conclusion and established that the first stage of the reaction is likely to be the formation of the iodohydrin derivatives of the epoxides with iodide. These groups presumably react with silver proteinate to produce silver in the second stage of the test. The reaction could be blocked by treating sections with either aqueous sulphuric acid, sulphuric acid in methanol, or boron trifluoride in methanol, reagents capable of converting epoxide groups in the cutin of the specimen to unreactive derivatives.