Environmental and Experimental Botany 71 (2011) 399–408 Contents lists available at ScienceDirect Environmental and Experimental Botany journal homepage: www.elsevier.com/locate/envexpbot Elevated CO 2 reduces the drought effect on nitrogen metabolism in barley plants during drought and subsequent recovery Anabel Robredo a , Usue Pérez-López a,∗ , Jon Miranda-Apodaca a , Maite Lacuesta b , Amaia Mena-Petite a , Alberto Mu ˜ noz-Rueda a a Departamento de Biología Vegetal y Ecología, Facultad de Ciencia y Tecnología, Universidad del País Vasco/EHU, Apdo. 644, E-48080 Bilbao, Spain b Departamento de Biología Vegetal y Ecología, Facultad de Farmacia, Universidad del País Vasco/EHU, P ◦ de la Universidad 7, E-01006 Vitoria-Gasteiz, Spain article info Article history: Received 7 July 2010 Received in revised form 1 February 2011 Accepted 13 February 2011 Keywords: Climate change Drought Elevated CO2 Hordeum vulgare Nitrogen metabolism abstract The objective of this study was to determine the response of nitrogen metabolism to drought and recov- ery upon rewatering in barley (Hordeum vulgare L.) plants under ambient (350 mol mol -1 ) and elevated (700 mol mol -1 ) CO 2 conditions. Barley plants of the cv. Iranis were subjected to drought stress for 9, 13, or 16 days. The effects of drought under each CO 2 condition were analysed at the end of each drought period, and recovery was analysed 3 days after rewatering 13-day droughted plants. Soil and plant water status, protein content, maximum (NR max ) and actual (NR act ) nitrate reductase, glutamine synthetase (GS), and aminant (NADH-GDH) and deaminant (NAD-GDH) glutamate dehydrogenase activ- ities were analysed. Elevated CO 2 concentration led to reduced water consumption, delayed onset of drought stress, and improved plant water status. Moreover, in irrigated plants, elevated CO 2 produced marked changes in plant nitrogen metabolism. Nitrate reduction and ammonia assimilation were higher at elevated than at ambient CO 2 , which in turn yielded higher protein content. Droughted plants showed changes in water status and in foliar nitrogen metabolism. Leaf water potential ( w ) and nitrogen assim- ilation rates decreased after the onset of water deprivation. NR act and NR max activity declined rapidly in response to drought. Similarly, drought decreased GS whereas NAD-GDH rose. Moreover, protein con- tent fell dramatically in parallel with decreased leaf  w . In contrast, elevated CO 2 reduced the water stress effect on both nitrate reduction and ammonia assimilation coincident with a less-steep decrease in  w . On the other hand,  w practically reached control levels after 3 days of rewatering. In parallel with the recovery of plant water status, nitrogen metabolism was also restored. Thus, both NR act and NR max activities were restored to about 75–90% of control levels when water supply was restored; the GS activity reached 80–90% of control values; and GDH activities and protein content were similar to those of control plants. The recovery was always faster and slightly higher in plants grown under elevated CO 2 conditions compared to those grown in ambient CO 2 , but midday  w dropped to similar values under both CO 2 conditions. The results suggest that elevated CO 2 improves nitrogen metabolism in droughted plants by maintaining better water status and enhanced photosynthesis performance, allowing superior nitrate reduction and ammonia assimilation. Ultimately, elevated CO 2 mitigates many of the effects of drought on nitrogen metabolism and allows more rapid recovery following water stress. © 2011 Elsevier B.V. All rights reserved. Abbreviations: A, carbon assimilation rate; DW, dry weight; EDTA, ethylenediaminetetraacetic acid; w, water potential; -GHM, gamma-glutamyl hydroxamate; GS, glutamine synthetase; GOGAT, glutamate synthase; HEPES, N-2-hydroxyethylpiperazine-N ′ -2-ethanesulfonic acid; NAD-GDH, deaminant glu- tamate dehydrogenase; NADH-GDH, aminant glutamate dehydrogenase; NRact , actual nitrate reductase; NRmax, maximum nitrate reductase; RSWC, relative soil water content; SDW, soil dry weight; SFW, soil fresh weight; SFW i , initial soil fresh weight. ∗ Corresponding author. Tel.: +34 94 601 5318; fax: +34 94 601 3500. E-mail addresses: anabel.robredo@ehu.es (A. Robredo), usue.perez@ehu.es (U. Pérez-López), j.miranda.apodaca@gmail.com (J. Miranda-Apodaca), maite.lacuesta@ehu.es (M. Lacuesta), amaia.mena@ehu.es (A. Mena-Petite), a.munoz-rueda@ehu.es (A. Mu ˜ noz-Rueda). 1. Introduction Recent environmental factors, such as increasing carbon diox- ide, climate change, and the resulting augmentation of drought, involve inevitable changes in the supply and metabolism of bio- logical elements, such as nitrogen (Urabe et al., 2010). Nitrate is the main nitrogen source in agricultural soils and frequently lim- its plant growth. The ability of plants to acquire and assimilate nitrate depends on soil nitrogen availability as well as plant uptake and assimilation capacity. Nitrate, taken up by NO 3 - transporters, is reduced to ammonium by the sequential reactions of nitrate reductase (NR) in the cytosol and nitrite reductase (NiR) in the plastids/chloroplasts. Afterwards, ammonium derived from nitrate reduction is converted first to glutamine by glutamine synthetase 0098-8472/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.envexpbot.2011.02.011