A physiological and molecular study of the effects of nickel deficiency and phenylphosphorodiamidate (PPD) application on urea metabolism in oilseed rape (Brassica napus L.)
Arkoun, Mustapha | Jannin, Laetitia | Laine, Philippe | Etienne, Philippe | Masclaux-Daubresse, Celine | Citerne, Sylvie | Garnica, Maria | Garcia-Mina, Jose-Maria | Yvin, Jean-Claude | Ourry, Alain | Ecophysiologie Végétale, Agronomie et Nutritions (EVA) ; Université de Caen Normandie (UNICAEN) ; Normandie Université (NU)-Normandie Université (NU)-Institut National de la Recherche Agronomique (INRA) | Institut Jean-Pierre Bourgin (IJPB) ; Institut National de la Recherche Agronomique (INRA)-AgroParisTech | Timac Agro Spain ; | Timac - Agro International | Pole de competitivite Mer-Bretagne; Fond Unique Inter-ministeriel
Urea is the major nitrogen (N) form supplied as fertilizer in agriculture. However, urease, a nickel-dependent enzyme, allows plants to use external or internally generated urea as a nitrogen source. Since a urease inhibitor is frequently applied in conjunction with urea fertilizer, the N-metabolism of plants may be affected. The aim of this study was to determine physiological and molecular effects of nickel deficiency and a urease inhibitor on urea uptake and assimilation in oilseed rape. Plants were grown on hydroponic solution with urea as the sole N source under three treatments: plants treated with nickel (+Ni) as a control, without nickel (-Ni) and with nickel and phenylphosphorodiamidate (+Ni+PPD). Urea transport and assimilation were investigated. The results show that Ni-deficiency or PPD supply led to reduced growth and reduced N-15-uptake from urea. This effect was more pronounced in PPD-treated plants, which accumulated high amounts of urea and ammonium. Thus, Ni-deficiency or addition of PPD, limit the availability of N and decreased shoot and root amino acid content. The up-regulation of BnDUR3 in roots indicated that this gene is a component of the stress response to nitrogen-deficiency. A general decline of glutamine synthetase (GS) activity and activation of glutamate dehydrogenase (GDH) and increases in its expression level were observed in control plants. At the same time, in (-N) or (+Ni+PPD) treated plants, no increases in GS or GDH activities and expression level were found. Overall results showed that plants require Ni as a nutrient (while most widely used nutrient solutions are devoid of Ni), whether they are grown with or without a urea supply, and that urease inhibitors may have deleterious effects at least in hydroponic grown oilseed rape.
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