PERCEPTION OF FREE CUTIN MONOMERS BY PLANT-CELLS

Enzymatic degradation of plant cuticles by fungal pathogens results in the release of free cutin monomers. The hypothesis that free cutin mo nomers are recognized by plant cells as endogenous stress-related sign als was tested in a model system consisting of cultured potato cells. Addition of cutin monomers in the micromolar range induced a transient alkalinization of the culture medium, similar to that observed with c hitin or chitotetraose that served as positive control. The cutin mono mers tested varied considerably in their potential to induce alkaliniz ation, the most and least active compounds being cis-g,10-epoxy-18-hyd roxystearic acid and palmitic acid, respectively. n,16-dihydroxypalmit ic acid (n = 8, 9 or 10) was found to be the major component of potato leaf cuticle and was among the most active cutin monomers. 9,10-Dihyd roxystearic acid, an analogue of the cutin monomer threo-9,10,18-trihy droxystearic acid, exhibited biological activity in a stereoselective manner, only the naturally occurring threo-stereoisomer inducing a rap id and strong alkalinization response. Alkalinization of the culture m edium was inhibited by addition of the protein-kinase inhibitor K-252a , and the onset of alkalinization was paralleled by changes in phospho rylation of specific proteins. The active cutin monomers also stimulat ed the production of the plant stress hormone ethylene and activated d efence-related genes at the mRNA level. The data provide evidence for a role of enzymatic breakdown products of plant cuticles as a new clas s of endogenous signal molecules.