Comparison of selenite and selenate in alleviation of drought stress in Nicotiana tabacum L.

Exogenous selenium (Se) improves the tolerance of plants to abiotic stress. However, the effects and mechanisms of different Se species on drought stress alleviation are poorly understood. This study aims to evaluate and compare the different effects and mechanisms of sodium selenate (NaSeO) and sodium selenite (NaSeO) on the growth, photosynthesis, antioxidant system, osmotic substances and stress-responsive gene expression of Nicotiana tabacum L. under drought stress. The results revealed that drought stress could significantly inhibit growth, whereas both NaSeO and NaSeO could significantly facilitate the growth of N. tabacum under drought stress. However, compared to NaSeO, Se application as NaSeO induced a significant increase in the root tip number and number of bifurcations under drought stress. Furthermore, both NaSeO and NaSeO displayed higher levels of photosynthetic pigments, better photosynthesis, and higher concentrations of osmotic substances, antioxidant enzymes, and stress-responsive gene (NtCDPK2, NtP5CS, NtAREB and NtLEA5) expression than drought stress alone. However, the application of NaSeO showed higher expression levels of the NtP5CS and NtAREB genes than NaSeO Both NaSeO and NaSeO alleviated many of the deleterious effects of drought in leaves, which was achieved by reducing stress-induced lipid peroxidation (MDA) and HO content by enhancing the activity of antioxidant enzymes, while NaSeO application showed lower HO and MDA content than NaSeO application. Overall, the results confirm the positive effects of Se application, especially NaSeO application, which is markedly superior to NaSeO in the role of resistance towards abiotic stress in N. tabacum.