Inadequate root uptake may represent a major component limiting rice to use urea as sole nitrogen source for growth

Both Free Indole-3-Acetic Acid and Photosynthetic Performance are Important Players in the Response of Medicago truncatula to Urea and Ammonium Nutrition Under Axenic Conditions

“…Growing crop plants using NH or urea as the only N source under axenic conditions is a poorly examined method. Few studies are performed under these conditions, especially in plants grown with urea (Gerendás et al, 1998 ; Wang et al, 2013 ; Yang et al, 2015 ), and it is therefore a challenging task. Appropriate control of the pH in the medium after the sterilization process is important to achieve the correct growth of plants and appropriate evaluation of urea or NH nutrition treatments because the autoclaving process may change the pH of the solution when certain nutrients are autoclaved together (see the Materials and Methods).…”

“…The urea-treated plants showed significant growth reduction on a fresh weight basis, compared with the plants grown under NO nutrition, but to a lesser extent than the NH -grown seedlings, as described for a number of plant species (Houdusse et al, 2005 ; Mérigout et al, 2008 ; Garnica et al, 2010 ; Yang et al, 2015 ). Indeed, various authors have reported that plants fed with urea suffer from N deficiency due to an extremely low urea uptake rate (Arkoun et al, 2012 ; Wang et al, 2013 ). However, the recent description of efficient urea transporters (Kojima et al, 2007 ; Wang et al, 2008 ; Zanin et al, 2014 ; Liu et al, 2015 ) confirms the possibility that plants may use urea the sole nitrogen source, with the compound being assimilated and translocated by plants (Mérigout et al, 2008 ).…”

“…In general, similar effects on plants to those described for NH have been reported for urea, but with a lower intensity (Houdusse et al, 2005 ). Although the understanding of NH utilization has improved in the last two decades (Gerendás et al, 1998 ; Witte et al, 2002 ; Mérigout et al, 2008 ; Zanin et al, 2014 , 2015 ), the physiological aspects of urea acquisition in plants grown under axenic conditions have only been investigated in Arabidopsis and rice (Wang et al, 2013 ; Yang et al, 2015 ). Therefore, there are still important gaps in our knowledge of the mechanisms of nitrogen nutrition in plants under axenic conditions, including the role of urea as an accessible nitrogen source for crops.…”

Physiological dissection revealed that both uptake and assimilation are the major components regulating different growth responses of two tobacco cultivars to nitrogen nutrition

“…Activity of GS was assayed as described in Wang et al . () with slight modifications. Protein enzymatic reaction was started by mixing 10 μl protein extract with 10 μl Milli‐Q water and 80 μl reaction buffer (100 m m MOPS, pH 7, 30 m m L‐glutamine, 1 m m MnCl 2 , 10 m m sodium arsenate, 80 m m hydroxylamine).…”

“…Ammonium was analysed as described in Wang et al . (). N content and total N per plant (shoots and roots) were determined using the Kjeldahl method as described (Nelson & Sommers ).…”