Interactive effects of selenium and arsenic on growth, antioxidant system, arsenic and selenium species of Nicotiana tabacum L.

• The moderate dose of Se/As in solution promoted the growth of FCT.
• Different Se/As levels in solution affects the ratios of Se/As species of FCT.
• Se mitigates As toxicity by improving the antioxidant capacity.
• Se mitigates As toxicity by influencing on the Se/As species of FCT changes.

This paper is aimed to study separate and interactive effects of selenium (Se) (selenite, 0–5 mg L−1) and arsenic (As) (arsenate, 0–5 mg L−1) on the growth and the antioxidant system of flue-cured tobacco (FCT) as well as the contents and species of As and Se in FCT through a hydroponic experiment and clarify the possible mechanism how Se alleviates the toxicity of As. The results were: single addition of Se (≤1 mg L−1) or As (1 mg L−1) by a low dose could stimulate the growth of FCT, but the growth of FCT would be inhibited when Se (5 mg L−1) or As (5 mg L−1) was added by a high dose. Low As levels stimulated the uptake of Se but high levels of As posing the opposite effects with the low Se dosage. However, the addition of As always inhibited the uptake of Se with high Se levels. Moreover, Se showed dual effects on the uptake of As. At the low As dose (1 mg L−1), the addition of Se inhibited the growth of FCT, but significantly promoted the activity of superoxide dismutase (SOD) and peroxidase (POD) enzymes as well as the content of MDA. Meanwhile, the percentages of organic Se and As(III) in the leaves of FCT declined with the increasing Se dose. However, the addition of Se by a moderate dose (0.1 mg L−1) alleviated the toxicity of the high As dose (5 mg L−1) and promoted the growth of FCT by elevating the ability of anti-oxidative stress of FCT and reducing the contents of MDA and As in FCT. The Se species in the leaves of FCT existed in organic ones (SeCys and SeMet) (100%), while the major As speciation was As(III) (75%). Likewise, the addition of As counteracted the toxicity of high Se dose (5 mg L−1) and promoted the growth of FCT slightly as it reduced the formation of organic Se or failed to transform excess inorganic Se species into organic ones and depressed the contents of Se in the roots and leaves of FCT. In a word, the low Se dose (0.1 mg L−1) alleviated of the toxicity of the high As dose and the addition of As counteracted the toxicity of high Se dose (5 mg L−1), as a result of which the promotion of the growth of FCT were realized.