title: γ-Aminobutyric acid addition alleviates ammonium toxicity by limiting ammonium accumulation in rice (Oryza sativa) seedlings.
abstract: Excessive use of nitrogen (N) fertilizer has increased ammonium (NH4+) accumulation in many paddy soils to levels that reduce rice vegetative biomass and yield. Based on studies of NH4+toxicity in rice (Oryza sativa, Nanjing 44) seedlings cultured in agar medium, we found that NH4+concentrations above 0.75 mM inhibited the growth of rice and caused NH4+accumulation in both shoots and roots. Use of excessive NH4+also induced rhizosphere acidification and inhibited the absorption of K, Ca, Mg, Fe and Zn in rice seedlings. Under excessive NH4+conditions, exogenous γ-aminobutyric acid (GABA) treatment limited NH4+accumulation in rice seedlings, reduced NH4+toxicity symptoms and promoted plant growth. GABA addition also reduced rhizosphere acidification and alleviated the inhibition of Ca, Mg, Fe and Zn absorption caused by excessive NH4+. Furthermore, we found that the activity of glutamine synthetase/NADH-glutamate synthase (GS; EC 6.3.1.2/NADH-GOGAT; EC1.4.1.14) in root increased gradually as the NH4+concentration increased. However, when the concentration of NH4+is more than 3 mM, GABA treatment inhibited NH4+-induced increases in GS/NADH-GOGAT activity. The inhibition of ammonium assimilation may restore the elongation of seminal rice roots repressed by high NH4+. These results suggest that mitigation of ammonium accumulation and assimilation is essential for GABA-dependent alleviation of ammonium toxicity in rice seedlings.
authors.affiliation: College of Life Sciences, Nanjing Agricultural University, Nanjing, 210095, China.
authors.forename: Xiaoling
authors.initials: X
authors.lastname: Ma
authors.affiliation: College of Life Sciences, Nanjing Agricultural University, Nanjing, 210095, China.
authors.forename: Changhua
authors.initials: C
authors.lastname: Zhu
authors.affiliation: College of Life Sciences, Nanjing Agricultural University, Nanjing, 210095, China.
authors.forename: Na
authors.initials: N
authors.lastname: Yang
authors.affiliation: College of Life Sciences, Nanjing Agricultural University, Nanjing, 210095, China.
authors.forename: Lijun
authors.initials: L
authors.lastname: Gan
authors.affiliation: College of Life Sciences, Nanjing Agricultural University, Nanjing, 210095, China.
authors.forename: Kai
authors.initials: K
authors.lastname: Xia
mesh_terms: D064751:Ammonium Compounds / Q000032:analysis / Q000378:metabolism*; D050790:Glutamate Synthase (NADH) / Q000378:metabolism; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D012275:Oryza / Q000737:chemistry / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D018517:Plant Roots / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D018520:Plant Shoots / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D058441:Rhizosphere; D036226:Seedlings / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
chemical_list: D064751:Ammonium Compounds; D005680:gamma-Aminobutyric Acid; D050790:Glutamate Synthase (NADH); D005974:Glutamate-Ammonia Ligase