Salt stress-induced proline accumulation and changes in tyramine and polyamine levels are linked to ionic adjustment in tomato leaf discs

The changes induced in the levels of proline, tyramine and polyamines in response to salt (NaCl) shock treatments were studied using tomato (Lycopersicon esculentum Mill.) leaf discs incubated in saline media supplemented with various concentrations of CaCl2 and KCl. When the leaf discs were subjected to high salinity (100-300 mM NaCl), they accumulated significant amounts of proline (Pro), tyramine, 1,3-diaminopropane (Dap), cadaverine (Cad)and agmatine (Agm) while their free polyamine (PA) content decreased. Under salinized conditions (250 mM NaCl), increase of Pro content in leaf tissues and CaCl2 concentration in the external medium were positively correlated. This correlation was even stronger doubling KCI concentration. Cad and Dap were also accumulated, while tyramine was not significantly modified. In contrast, the amount of free Agm, putrescine (Put), spermidine (Spd) and spermine (Spm) decreased to very low levels. Under non salinized conditions the amount of Put and Spd also deceased in response to the increase of CaCl2 concentration in the external medium and this effect was reinforced in presence of highest concentrations of KCl. While analyzing the changes in the internal ionic status of the leaf explants in response to the salt treatment, it became clear that the internal Na+ and Ca2+ levels exert a positive effect on Pro, tyramine, Agm and Dap levels and a negative one on the levels of Put and Spd. The physiological interest of these responses is discussed. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.