Ethylene production by the lichen ramalina duriaei

The lichen Ramalina duriaei evolved ethylene when in a wetted state, the rate of ethylene evolution being constant for at least the first 20 h. Inhibitors of the ACC (I-aminocyclopropane-I-carboxylic acid) pathway did not inhibit ethylene production. Metal ions stimulated the production, with Fe²⁺ being the most effective. This stimulation was not affected by inhibitors of the ACC pathway but was inhibited by free radical scavengers such as propylgallate and quercitin. Endogenous ACC content was similar whether the lichens were producing ethylene at a basal rate or during Fe²⁺-stimulated ethylene formation. Malondialdehyde and aldehyde contents were higher in the presence of Fe²⁺. The results are discussed in terms of known pathways of ethylene production by micro-organisms.