Ornithine-induced increase of proline and polyamines contents in tobacco cells under salinity conditions

Abstract

Majority of injuries observed in plants caused by salinity are associated with the induction of oxidative stress. The accumulation of reactive oxygen species is overwhelmed by the activities of scavenging enzymes and nonenzyme agents, e.g., proline and polyamines that are commonly synthesized directly from ornithine. The present study was undertaken to evaluate the impact of ornithine, as the common source of proline and polyamines, in the biosynthesis of proline and polyamines and in the activation of antioxidant enzymes in the tobacco cells under saline conditions. Six-day-old cells were treated with 50 mM NaCl and 0.5 mM ornithine. These concentrations were selected based on the results of two sets of preliminary studies using different concentrations of ornithine and NaCl. The results demonstrated that the production of proline and putrescine/spermidine was stimulated by ornithine under normal and stress conditions. Ornithine, in the presence or absence of NaCl, significantly increased the antioxidant enzyme activity (up to 325% for catalase, 270% for peroxidase, and 374% for superoxide dismutase), compared to those of the control group. Treatment with ornithine reduced H2O2 to the levels observed in the control cells, while NaCl increased it to 173% of the control. In all treatments, the level of lipid peroxidation was higher than that in the control cells and suppressed the growth of the tobacco cells. On the basis of the results, the treatment of the tobacco cells with ornithine elevates the proline and polyamine contents, with a concurrent decrease in H2O2 content.