Fluid Composition and Factors that Elicit Secretion by the Trap Lobes of Dionaea muscipula Ellis

Abstract

Summary The chemical requirements for the elicitation of the secretion of digestive fluid by the trap lobes of Dionaea muscipula Ellis (Venus's Flytrap) were examined and the mineral ion and organic solute composition of the secreted fluid determined. A wide range of low molecular weight nitrogen compounds were found to cause the secretion of both Cl- and acid proteolytic activity when given at concentrations of 1 or 10 mM. Salts of the alkali metals were similarly effective while alkaline earth and transition metal salts and salt-free protein suspensions were inactive. The digestive fluid has an average osmolarity of 10–14 mosM. Cl- is usually present at 5–10 mEq and constitutes more than 90 per cent of the contribution of anions to the total osmolarity and between 70 and 100 per cent of the contribution of free anions to the electrical charge balance of the secretion. H+'s ore the principal monovalent cation in the fluid and are found at an average activity of 1–2 mEq while K+, Na+, Mg++ and Ca++ are each present at concentrations of less than 1 mM. Short-chain carboxylic acids, including formic acid, could not be detected in the secretion but low concentrations of glycerol, inositol, glucose, an unidentified dimeric sugar and several long-chain fatty acids were found. It is proposed that HC1 is responsible for the acidity of the digestive fluid and that a major effect of secretion elicitors is to initiate the discharge of this mineral acid from the digestive glands. The source and significance of the organic constituents of the secretion remains to be determined.