Increased endogenous potassium-enhanced nicotine accumulation and sugar decomposition in flue-cured tobacco leaves
In order to increase endogenous potassium levels in tobacco leaves, an expression vector was constructed for the HAK1 gene (putative high-affinity potassium transporter) of Nicotiana tabacum driven by the rbcS gene promoter. HAK1-overexpressing tobacco lines were obtained after transformation of flue-cured tobacco cultivar K326, and the transformants were verified by PCR and Southern blot assays. The expression levels of HAK1 and the potassium channel TORK1 were apparently increased, with the highest expression levels being 58.9-fold and 15.7-fold greater, respectively, than in wild type. The activity of root ATPase and the potassium content in fresh leaves of HAK1-overexpressing plants were both increased, but they decreased with increasing concentrations of external potassium in the culture solution. The general chemical components of flue-cured cutters overexpressing HAK1 were changed, and showed a trend of potassium and nicotine increasing and sugar decreasing, in which the average potassium content was up to 24.3%. This demonstrated that the HAK1 gene functions in increasing potassium and then improving the C/N ration in tobacco leaves, and could be useful in breeding for future production of less harmful tobacco.