β-Cyclodextrin–hemin enhances tolerance against salinity in tobacco seedlings by reestablishment of ion and redox homeostasis

β-Cyclodextrin–hemin (β-CDH) is a complex combining hemin with β-cyclodextrin (β-CD), which could improve hemin solubility. Our previous results showed that β-CDH, was able to enhance alfalfa tolerance against cadmium stress. However, whether or how β-CDH influences salinity tolerance is still elusive. In this report, we observed that similar to the beneficial responses of hemin rather than β-CD, the addition of β-CDH not only alleviated salinity-induced seedling growth inhibition (in particular), but also arrested chlorophyll degradation in tobacco seedlings. The efficiency of β-CDH against salinity stress compared to that of hemin, was confirmed, since the maximum beneficial responses against NaCl stress was obtained with 0.1 μM β-CDH and 10 μM hemin, respectively. Subsequent work showed that the redox imbalance caused by salinity stress could be improved by β-CDH. This was suggested by the reduced lipid peroxidation and hydrogen peroxide accumulation, as well as the induction of representative antioxidant genes, encoding superoxide dismutase, guaiacol peroxidase, and ascorbate peroxidase. Meanwhile, compared to control conditions, the ratio of K+ to Na+ was relatively low in NaCl-stressed tobacco seedlings. By contrast, the administration of β-CDH not only significantly blocked the increase of Na+, but also obviously increased K+, thus resulting in a high K+ to Na+ ratio in both shoot and root parts. Ion homeostasis is therefore reestablished. Together, our results suggested that β-CDH was able to improve salinity tolerance via the reestablishment of redox and ion homeostasis.