Free spermidine and spermine content in Lotus glaber under long-term salt stress

Polyamine metabolism has long been involved in plant stress responses, although physiological roles of putrescine, spermidine and spennine are still under debate. Regarding long-term salinization, it have been suggested that high titers of spermidine and/or spermine, but not putrescine, are correlated with the response of plants to salinity. In this work, we use the moderately salt tolerant glycophyte Lotus glaber as a model to test the hypothesis that free spermidine and spermine are biochemical indicators of salt stress response. For such purpose, we evaluated polyamine content in three different long-term salt stress approaches: germinating and growing seedlings under salinity, salinization of growing plants and imposition of salt stress to clone stem cuttings obtained from plants recovered from saline lowlands. Proline was also tested to evaluate if polyamines levels correlate with this compatible solute response. Results from these experiments showed a similar trend concerning higher polyamines content i.e., a salt induced a decrease of free spermidine and an increase of free spermine, in line with the idea that polyamine are biochemical indicators of salt stress. However, polyamine levels not always paralleled the accumulation of proline. These observations are discussed with regard of the putative roles reported for polyamines in plant abiotic stresses. (C) 2004 Elsevier Ireland Ltd. All rights reserved.