Root phosphoenolpyruvate carboxylase and NAD-malic enzymes activity increase the ammonium-assimilating capacity in tomato.
Plant ammonium tolerance has been associated with the capacity to accumulate large amounts of ammonium in the root vacuoles, to maintain carbohydrate synthesis and especially with the capacity of maintaining high levels of inorganic nitrogen assimilation in the roots. The tricarboxylic acid cycle (TCA) is considered a cornerstone in nitrogen metabolism, since it provides carbon skeletons for nitrogen assimilation. The hypothesis of this work was that the induction of anaplerotic routes of phosphoenolpyruvate carboxylase (PEPC), malate dehydrogenase (MDH) and malic enzyme (NAD-ME) would enhance tolerance to ammonium nutrition. An experiment was established with tomato plants (Agora Hybrid F1) grown under different ammonium concentrations. Growth parameters, metabolite contents and enzymatic activities related to nitrogen and carbon metabolism were determined. Unlike other tomato cultivars, tomato Agora Hybrid F1 proved to be tolerant to ammonium nutrition. Ammonium was assimilated as a biochemical detoxification mechanism, thus leading to the accumulation of Gln and Asn as free amino acids in both leaves and roots as an innocuous and transitory store of nitrogen, in addition to protein synthesis. When the concentration of ammonium in the nutrient solution was high, the cyclic operation of the TCA cycle seemed to be interrupted and would operate in two interconnected branches to provide α-ketoglutarate for ammonium assimilation: one branch supported by malate accumulation and by the induction of anaplerotic PEPC and NAD-ME in roots and MDH in leaves, and the other branch supported by stored citrate in the precedent dark period.
Dpto. Biología Vegetal y Ecología, Universidad del País Vasco, UPV/EHU Apdo. 644, 48080 Bilbao, Spain. Electronic address: igor.setien@ehu.es.
Igor
I
Setién
Dpto. Biología Vegetal y Ecología, Universidad del País Vasco, UPV/EHU Apdo. 644, 48080 Bilbao, Spain. Electronic address: iavega001@ikasle.ehu.es.
Izargi
I
Vega-Mas
Dpto. Biología Vegetal y Ecología, Universidad del País Vasco, UPV/EHU Apdo. 644, 48080 Bilbao, Spain. Electronic address: natalia.siurana@gmail.com.
Natalia
N
Celestino
Instituto de Agrobiotecnología, IdAB-CSIC-Universidad Pública de Navarra-Gobierno de Navarra, Campus de Arrosadía, E-31006 Pamplona, Spain. Electronic address: maren.calleja@unavarra.es.
María Eréndira
ME
Calleja-Cervantes
Dpto. Biología Vegetal y Ecología, Universidad del País Vasco, UPV/EHU Apdo. 644, 48080 Bilbao, Spain. Electronic address: carmen.gmurua@ehu.es.
Carmen
C
González-Murua
Dpto. Biología Vegetal y Ecología, Universidad del País Vasco, UPV/EHU Apdo. 644, 48080 Bilbao, Spain. Electronic address: jm.estavillo@ehu.es.
José María
JM
Estavillo
Dpto. Biología Vegetal y Ecología, Universidad del País Vasco, UPV/EHU Apdo. 644, 48080 Bilbao, Spain. Electronic address: mariabegona.gonzalez@ehu.es.
María Begoña
MB
González-Moro
D064751:Ammonium Compounds / Q000378:metabolism*; D002244:Carbon / Q000378:metabolism; D002952:Citric Acid Cycle; D004591:Electrophoresis, Polyacrylamide Gel; D007656:Ketoglutaric Acids / Q000378:metabolism; D018551:Solanum lycopersicum / Q000201:enzymology / Q000378:metabolism*; D008291:Malate Dehydrogenase / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism; D010730:Phosphoenolpyruvate Carboxylase / Q000378:metabolism*; D018517:Plant Roots / Q000201:enzymology* / Q000378:metabolism
D064751:Ammonium Compounds; D007656:Ketoglutaric Acids; D002244:Carbon; D008291:Malate Dehydrogenase; C046446:malate dehydrogenase-(oxaloacetate-decarboxylating) (NAD+); D010730:Phosphoenolpyruvate Carboxylase; D009584:Nitrogen
Ammonium nutrition; Glutamate dehydrogenase; Glutamine synthetase; Isocitrate dehydrogenase; Solanum lycopersicum Mill.; TCA cycle