Abstract
Despite the widespread use of urease inhibitors in agriculture, little information is available on their effect on nitrogen (N) uptake and assimilation. Aim of this work was to study, at physiological and transcriptional level, the effects of N-(n-butyl) thiophosphoric triamide (NBPT) on urea nutrition in hydroponically grown maize plants. Presence of NBPT in the nutrient solution limited the capacity of plants to utilize urea as a N-source; this was shown by a decrease in urea uptake rate and 15N accumulation. Noteworthy, these negative effects were evident only when plants were fed with urea, as NBPT did not alter 15N accumulation in nitrate-fed plants. NBPT also impaired the growth of Arabidopsis plants when urea was used as N-source, while having no effect on plants grown with nitrate or ammonium. This response was related, at least in part, to a direct effect of NBPT on the high affinity urea transport system. Impact of NBPT on urea uptake was further evaluated using lines of Arabidopsis overexpressing ZmDUR3 and dur3-knockout; results suggest that not only transport but also urea assimilation could be compromised by the inhibitor. This hypothesis was reinforced by an over-accumulation of urea and a decrease in ammonium concentration in NBPT-treated plants. Furthermore, transcriptional analyses showed that in maize roots NBPT treatment severely impaired the expression of genes involved in the cytosolic pathway of ureic-N assimilation and ammonium transport. NBPT also limited the expression of a gene coding for a transcription factor highly induced by urea and possibly playing a crucial role in the regulation of its acquisition. This work provides evidence that NBPT can heavily interfere with urea nutrition in maize plants, limiting influx as well as the following assimilation pathway.
Highlights
Urea is the most frequently used nitrogen (N) fertilizers in the world with annual amount of over 50 million tons accounting for more than 50% of the world N fertilizer consumption (International Fertilizer Industry Association, 2008)
Morphological Traits of Maize Plants Treated with Urea and N-(n-butyl) thiophosphoric triamide (NBPT)
Maize plants grown for 1 week under hydroponic conditions in presence of urea (Urea treatment) showed an increased shoot biomass and length in comparison to Control plants grown without N supply (Figures 1 and 2)
Summary
Urea is the most frequently used nitrogen (N) fertilizers in the world with annual amount of over 50 million tons accounting for more than 50% of the world N fertilizer consumption (International Fertilizer Industry Association, 2008). The incredible increase in urea fertilizer use during the last decades is mainly due to its competitive price and the high N content (46% of mass), that allow reducing transport and distribution costs (Miller and Cramer, 2004). Besides using inorganic N sources, plants, including crops, have been shown to be able to take up intact urea (for review, see Kraiser et al, 2011; Nacry et al, 2013). Maize plants possess dedicated transmembrane transport systems in root cells for the acquisition of urea with high and low affinity, mediated by a DUR3 transporter and aquaporins, respectively (Gaspar et al, 2003; Gu et al, 2012; Zanin et al, 2014; Liu et al, 2015; Yang et al, 2015)
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