EFFECTS OF NACL AND MANNITOL ISOSMOTIC STRESSES ON THE FREE POLYAMINELEVELS IN LEAF DISCS OF TOMATO SPECIES DIFFERING IN SALT TOLERANCE

Short-term changes in free polyamines induced by salt (200 mmol/L NaCl ) and osmotic (400 mmol/L mannitol) stresses were determined in leaf d iscs of the salt-sensitive cultivated tomato species (Lycopersicon esc ulentum) and its wild salt-tolerant relative L. pennellii with the obj ective of checking whether these metabolites could be used as early tr aits of tolerance. In L. pennellii, a putrescine and spermidine accumu lation was found in the osmotically-stressed leaf discs from 30 min un til the end of the experiment (2 h). Under salt stress, the free polya mine accumulation in L. pennellii only took place during the first: 15 min, mainly due to putrescine, whereas its levels decreased after thi s time. These results suggest that the initial polyamine accumulation was due to the osmotic effect induced by salinity, but the levels rapi dly began to decrease as the saline ions were accumulated from the med ium. In a similar manner to the wild species, the leaf discs of L. esc ulentum submitted to salt stress also accumulated Na+ from the beginni ng of the experiment, although the accumulation was slower. Neverthele ss, the patterns of free polyamines were similar under both salt and o smotic stresses in L. esculentum, which suggests that the results only show the osmotic shock. In this species, the polyamine levels tended to decrease at the beginning of the experiment, whereas the opposite r esponse was observed at the end of the period (between 1 and 2 h). The results obtained show that the polyamine levels change in a very diff erent way in the leaf discs of both tomato species. Moreover, NaCl str ess and non-ionic osmotic stress caused by mannitol are separable only in the salt-tolerant species in terms of their effects on free polyam ine levels.