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ppl1712-sup-0001-FigureS1.pdfPDF document68K Fig. S1. Effect of NH4+ concentration and light intensity on plant growth and carbohydrates content. (A) Total plant growth (g DW); (B) 1total carbohydrates content (mmol g−1 DW) for pea plants grown under control (⦿) or high-light conditions (○). Data represent average values ± se (A: n = 8; B: n = 3). The letters represent significant differences between NH4+ concentrations for higher light (A, B, C and D) and control conditions (a, b, c and d). An asterisk (*) denotes a significant difference between higher light and control conditions for each NH4+ concentration (P ≤ 0.05). 1Soluble carbohydrates (fructose, glucose and sucrose) and starch expressed as mmol of glucose g−1 DW (Ariz et al. 2011).
ppl1712-sup-0002-AppendixS2.pdfPDF document191K Fig. S2. A scheme showing two possible global metabolic responses of NH4+-fed plants to deal with NH4+ toxicity. On the left, a mechanism of tolerance to NH4+ toxicity; HLI induces higher C availability which is accompanied by higher root ATP content and respiration rates. This extra energy availability is related to the internal NH4+ content regulation (probably NH4+ influx/efflux) and to an improvement of the cell ionic balance resulting in an improved regulation of C and N flows in response to NH4+ nutrition in pea plants. On the right, a mechanism of response to NH4+ toxicity; NH4+ nutrition at high concentrations results in acute changes to C–N metabolism indicating a severe C and energy limitation under these conditions. Several anaplerotic enzymes, PEPC, ICDH and GDH, are induced in the roots to provide C intermediates. In addition, amino acid synthesis is diverted toward lower C/N ratio amino acid pathways and secondary N compound production. High internal NH4+ content is detected in pea roots at such conditions. Note that the thickness of arrows represents the C and N flows between organelles and organs of pea plants grown under NH4+ conditions. Numbers indicate the key enzymes associated with the primary C–N metabolism; 1, PEPC, phosphoenolpyruvate carboxylase; 2, ICDH, cytosolic isocitrate dehydrogenase; 3, GDH, mitochondrial glutamate dehydrogenase; 4, AS, asparagine synthetase; 5, GS, glutamine synthetase; 6, GOGAT, glutamate synthase; 7, AAT, aspartate aminotransferase; 8, MDH, malate dehydrogenase; 9, IDH, mitochondrial isocitrate dehydrogenase.

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