Regulation of nitrate metabolism under low temperature, low nitrogen and low phosphorus stress. Transcription of nitrate transporters (NRT), nitrate reductase (NR) and nitrite reductase (NiR) are down-regulated under all three stress conditions, but by different control mechanisms. Under low N the limited availability of nitrate causes down-regulation of nitrate metabolisms, under low temperature and low P conditions on the other hand increases in the amino acid pool were responsible for control of nitrate metabolism. Heat maps show log2 values of fold changes stress/control; data behind NRT and NR are mean values from more than one transcript (see Additional file 5: Table S4); data for amino acid pool averages values from all measured amino acids. [GS- glutamine synthase; GOGAT – glutamate synthetase; 2OG – 2-oxoglutarate].