Improved callus induction, shoot regeneration, and salt stress tolerance in Arabidopsis overexpressing superoxide dismutase from Potentilla atrosanguinea

Superoxide dismutase (SOD) catalyzes the dismutation of superoxide radicals (O-2 (center dot) (-)) to molecular oxygen (O-2) and hydrogen peroxide (H2O2). Previously, we have identified and characterized a thermo-tolerant copper-zinc superoxide dismutase from Potentilla atrosanguinea (PaSOD), which retains its activity in the presence of NaCl. In the present study, we show that cotyledonary explants of PaSOD overexpressing transgenic Arabidopsis thaliana exhibit early callus induction and high shoot regenerative capacity than wild-type (WT) explants. Growth kinetic studies showed that transgenic lines have 2.6-3.3-folds higher growth rate of calli compared to WT. Regeneration frequency of calli developed from transgenic cotyledons was found to be 1.5-2.5-folds higher than that of WT explants on Murashige and Skoog medium supplemented with different concentrations of naphthalene acetic acid (NAA) and 6-benzylaminopurine (BAP) within 2 weeks. A positive regulatory effect of PaSOD and H2O2 was observed on different stages of callusing and regeneration. However, this effect was more pronounced at the early stages of the regeneration processes in transgenic lines as compared to WT. These results clearly indicate that plant regeneration is regulated by endogenous H2O2 and by factors, which enhance its accumulation. Transgenics also exhibited salt stress tolerance with higher SOD activity, chlorophyll content, total soluble sugars, and proline content, while lower ion leakage and less reduction in relative water content, as compared to WT. Thus, it appears that the activation of PaSOD at regeneration stage accompanied by increased H2O2 production can be one of the mechanisms controlling in vitro morphogenesis.