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 re sponse to salt (NaCl) shock treatments were studied using tomato (Lycopersi con esculentum Mill.) leaf discs incubated in saline media supplemented wit h various concentrations of CaCl2 and KCl. When the leaf discs were subject ed 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 sal inized conditions (250 mM NaCl), increase of Pro content in leaf tissues an d CaCl2 concentration in the external medium were positively correlated. Th is correlation was even stronger doubling KCI concentration. Cad and Dap we re also accumulated, while tyramine was not significantly modified. In cont rast, the amount of free Agm, putrescine (Put), spermidine (Spd) and spermi ne (Spm) decreased to very low levels. Under non salinized conditions the a mount of Put and Spd also deceased in response to the increase of CaCl2 con centration in the external medium and this effect was reinforced in presenc e of highest concentrations of KCl. While analyzing the changes in the inte rnal ionic status of the leaf explants in response to the salt treatment, i t became clear that the internal Na+ and Ca2+ levels exert a positive effec t 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.