Induction of ethylene biosynthesis in tobacco leaf discs by cell wall disesting enzymes

Cellulysin induces ethylene production in tobacco leaf discs by initiating the formation of 1-aminocyclopropane-1-carboxylic acid. Induction occurred within 30 to 60 min of incubation and was inhibited by aminoethoxyvinylglycine, and the antiproteases, PMSF and soybean trypsin inhibitor. Cycloheximide (CHI) at 2.8 μg/ml and chloramphenicol (CAP) at 100 μg/ml did not inhibit this induction although incorporation of the label from (3,4-¹⁴C)methionine into the acid-insoluble fraction was inhibited by 57%. At 14 μg/ml CHI, and CAP, ethylene production was inhibited by 25% while protein synthesis was inhibited by 75%. We suggest that either the low amounts of protein synthesis that appear to be insensitive to CHI is sufficient to induce ethylene biosynthesis or that Cellulysin activates a preexisting but inactive form of ACC synthase to promote ethylene biosynthesis. Also, induction of ethylene production by microbial enzymes that digests plant cell walls may be an initial protective response of plants that serves to combat microbial infection.