Uptake of jasmonic acid and related compounds by mesophyll protoplasts of the barley leaf

Jasmonic acid (JA) permeates the plasma membrane of mesophyll cells by diffusion as the lipophilic undissociated JAH molecule probably without the participation of a saturable uptake component. The mesophyll plasma membrane is nearly impermeable to the JA anion. The permeability coefficients of JA and several JA derivatives (its methyl ester (JAMe), 7-iso-cucurbic acid (7-iso-CA), 6-epi-7-iso-cucurbic acid (6-epi-7-iso-CA), and both stereoisomers of the JA leucine conjugate (+)-JA-Leu and (-)-JA-Leu)) were determined and used in a simplified mathematical model to predict stress-dependent JA redistribution between cytosol and apoplast in comparison with ABA. The redistribution of JA takes place similar to ABA; however, its velocity is much higher because of the high JA membrane permeability. When the permeability coefficients for the mesophyll plasma membrane are plotted double-logarithmically against the ratio of the distribution coefficient and the molecular ratio to the power of 1.5 (K(D)Mr(-1.5)), two straight lines result for two different classes of compounds. The permeability coefficients of JA conjugates are lower than that of the free acid by approximately one order of magnitude, but they are still significantly higher than that of ABA