Potassium (K), one of the essential elements required for plant growth and development, determines leaf quality in tobacco ( Nicotiana tabacum L.). Potassium (K) levels are relatively high in black soils (vertisols), but K uptake is severely hindered by the presence of remarkably high levels of calcium and magnesium. Our major objective was to enhance potassium uptake in black soils, which cover the major tobacco growing regions of Andhra Pradesh, India. Among several agronomic inputs such as soil amendments, fertilizer application, and plant growth regulators, we found that foliar application of fulvic acid (FA), one of the most bioactive humate molecules, enhanced K levels in leaves. Using next-generation sequencing (NGS), we identified changes in expression levels of a number of genes related to metabolic pathways implicated in plant growth and nutrient uptake upon FA application. Interestingly, starch levels in leaves were reduced concomitant with an increase in K attributable to FA application. We attempt to provide plausible reasons for these observed FA-induced changes. Our results suggested that FA acts in a manner similar to the plant hormone auxin in tobacco, influencing expression of key genes encoding transporters and enzymes involved in K uptake and Color versions of one or more of the figures in the article can be found online at www. tandfonline.com/wcim. 740 Downloaded by [McMaster University] at 22:49 26 December 2014Fulvic Acid and Nutrient Uptake 741 starch metabolism. While fulvic acid has beneficial effects on plant growth, its mechanism of action is still unclear.

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