NaCl- and ethylene-dependent cadaverine accumulation and its possible protective role in the adaptation of the common ice plant to salt stress

The accumulation of free polyamines is very important for plant resistance to abiotic stresses. In this study, a putative defensive role of free cadaverine (Cad) in the halophyte Mesembryanthemum crystallinum L. (the common ice plant) was studied. Under salinity conditions (500 mM NaCl), Cad accumulation was accompanied by enhanced ethylene (Eth) production in true leaves of the common ice plants. The involvement of Eth in Cad production was confirmed by detached leaf treatment with exogenous Eth. In experiments with etiolated seedlings of the common ice plants and Eth-insensitive arabidopsis mutant (ein4), it was shown that the interactions between Cad and Eth under stress conditions were especially essential for cell elongation. However, a NaCl-induced increase in the Cad content and Eth production was not related to expression of stress-induced PEPC gene (at the mRNA level). DNA protection by Cad from oxidative degradation in vitro in the hydroxyl radical-generating system was demonstrated. This polyamine was supposed to act as a free radical scavenger. A possible interaction between Eth production and Cad accumulation and its relevance to plant stress–adaptation are discussed.