Alleviation of cadmium toxicity by potassium supplementation involves various physiological and biochemical features in Nicotiana tabacum L.

Potassium (K+) plays important roles in the development of plants and the response to various environmental stresses. However, the involvement of potassium in alleviating heavy metal stress in tobacco remains elusive. Greenhouse hydroponic experiments were conducted to evaluate the alleviating effects of K+ on tobacco subjected to cadmium (Cd) toxicity using four different K+ levels. Dose-dependent increases of plant biomass were found in both 0-μM Cd and 5-μM Cd treatments under different K+ levels, with the exception of the 1-mM KHCO3 (K3) treatment. The best mitigation effect was recorded with the 0.5-mM K+ (K2) treatment, which greatly alleviated Cd-induced growth inhibition, photosynthesis reduction, and oxidative stress. Compared with K0 treatment (no KHCO3 addition), K2 treatment significantly reduced Cd uptake and translocation after 5 and 10 days of Cd treatment. Moreover, the net photosynthetic rate, intracellular CO2 concentration, stomatal conductance, and transpiration rate as well as K+, zinc, manganese, copper, and iron concentrations in both shoots and roots after 10 days of Cd treatment significantly improved under the K2 treatment, and malondialdehyde accumulation in both shoots and roots was repressed, compared with K0 + Cd. Superoxide dismutase was found to play key roles in alleviating Cd-induced oxidative pressure in shoots of plants in K2 treatment under Cd treatment. Our findings advocate a positive role for K+ in reducing pollutant residues for safe production, especially in soils slightly or moderately polluted with Cd.