Effects of exogenous ornithine enantiomers on tobacco cells under salinity conditions

Ornithine is a non-proteinogenic amino acid, which plays an essential role in the metabolism of plants. Regard to the chirality of the molecule, physiological response of the plant cells to its two enantiomers have not been widely investigated yet. In the present study, suspension-cultured tobacco cells were treated with 1 mM of D- and Lenantiomers of ornithine in normal conditions as well as under stress of 50 mM NaCl. Differential effects of L- and D-enanthiomers were observed either in normal or under salinity stress conditions. L-ornithin adversely affected the growth of tobacco cells in normal conditions and its detrimental effect was intensified by salinity. Treatment with D-ornithine however, not only did not change the growth but also alleviated it under salt stress. Physiological response of tobacco cells to D-ornithine in normal conditions was accompanied by increasing of polyamines. Under salinity stress however, D-ornithine treatment increased the activity of major antioxidant enzymes i.e., superoxide dismutase, catalase, and peroxidase and also increased proline content of the cells, all together resulted in lowering H2O2 and maintenance of cells membrane integrity. The results suggested that D-ornithine is a potent compound for activation of anti-oxidant system of plant cells and alleviation of stress condition.