RESPONSES IN POLYAMINE TITER UNDER OSMOTIC AND SALT STRESS IN SORGHUMAND MAIZE SEEDLINGS

Changes in leaf water potential, K+/Na+ ratio and in polyamine titers in maize (Zea mays L. cv. Pioneer 3950) and sorghum (Sorghum bicolor ( L.) Moench cv. ICSV 112) were investigated as the function of increasi ng equi-osmotic concentrations of NaCl or polyethylene glycol 6000 app lied for 3 days in the nutrient solution. For both treatments, sorghum responded with a more intensive decrease in leaf water potential comp ared with maize. Plant analysis showed that under salinity, a higher l evel of Na+ was accumulated in the roots of maize than in those of sor ghum while shoot Na+ concentrations were nearly the same. Internal Kconcentration was always higher in sorghum, leading to a K+/Na+ ratio 2 to 4-fold higher in the roots of sorghum compared with that in maize . In maize, NaCl and osmotic stresses evoked similar rates of polyamin e accumulation, while in sorghum, osmotic stress was more effective in comparison to salt treatment. In maize, spermidine was apparently abs ent, indicating its fast turnover. In sorghum, the accumulation of di- and polyamines was proportional to the strength of the osmotic stress and the impairment of polyamine synthesis was also observed at high d egrees of stress. The present data support the idea that the initiatio n of polyamine accumulation needs an osmotic signal; however, when a p ermeable ion is present, salt accumulation can contribute to the osmot ic adjustment and thus the onset of polyamine biosynthesis is delayed or does not take place. Some enzymes in the polyamine biosynthetic pat hway may be sensitive for high salinity and the biosynthetic processes shift towards oxidative degradation.