Effect of octanoic acid on ethylene-mediated processes in Arabidopsis

We have examined whether octanoic acid (OA) one of the short chain saturated fatty acids (SCSFA), increases ethylene response in the following three ethylene-mediated processes: a) hypocotyl growth in darkness; b) formation of new flowers; c) flower abscission. These processes were examined in the presence or absence of exogenous ethylene in Arabidopsis wild type (WT) and in the ethylene-insensitive mutants, etr1-3 and ein2-1 and in the ethylene over-producer mutant eto1-1. Our results show that OA decreased hypocotyl length of WT in the absence or presence of exogenous ethylene, apparently showing that OA acts via augmentation of ethylene action. However, the hypocotyl growth inhibition could not be ascribed to increased ethylene sensitivity since application of inhibitors of ethylene synthesis (aminoethoxyvinylglycine; AVG) or action (1-methylcyclopropene;1-MCP) to WT seedlings did not prevent specifically the OA-induced growth inhibition. Also, OA inhibited hypocotyl growth in the mutants etr1-3 and ein2-1 in a similar pattern to that obtained in WT. On the other hand, OA had no effect on flower formation neither in WT, etr1-3 and eto1-1, in which ethylene reduced flower formation, nor in the ein2-1 mutant, in which ethylene had no effect. OA also did not increase flower abscission in WT or in the mutants etr1-3 and ein2-1 neither in the absence nor in the presence of ethylene. However, OA has augmented flower abscission in the mutant eto1-1 only in the absence of exogenous ethylene. This result might indicate that the effect of OA on eto1-1 is specific to this mutant and is not due to general deleterious effects inflicted by OA. Taken together, our results show that in general OA does not augment ethylene response in Arabidopsis, but it might affect ethylene action in flower abscission of the ethylene-overproducer mutant.