Ethylene triggers salt tolerance in maize genotypes by modulating polyamine catabolism enzymes associated with H2O2 production

The current study was undertaken to investigate if there is a relationship between metabolisms of ethylene and polyamines in the processes of salinity acclimation of salt-tolerant and salt-sensitive maize genotypes. Biphasic ethylene production (at 5.5 and 12.5 h) was registered only in salt-sensitive plants during NaCl exposure. In the salt-tolerant genotype, the unique ethylene peak at 5.5 h was closely related to increased polyamine accumulation (a polyamine-dependent H2O2 signalling process), whereas the same did not occur in the salt-sensitive genotype. The absence of H2O2 signalling at 5.5 h in the salt-sensitive genotype was related to a burst in ethylene production at 12.5 h, known as 'stress ethylene', as well as a concomitant decrease in total polyamine content by salinity. The lack of stress ethylene synthesis in the salt-tolerant genotype was attributed to down-regulation of 1-aminocyclopropane-1-carboxylic acid oxidase (ACO) activity and ZmACO5b gene expression. Our findings suggest that ethylene is intimately involved in salt stress acclimation through activation of a complex pathway of signalling by H2O2 that is polyamine catabolism-dependent.