. 2020 Mar 24;71(15):4380–4392. doi: 10.1093/jxb/eraa150

Table 2.

Proton changes in the processes of N transport and assimilation

N utilization processes		Equation of H⁺ change in cytoplasm
NH₄⁺	NH₄⁺ transport	NH₄⁺_(out)→NH₃+H⁺_(out)
	NH₃ protonation	NH₃+1H⁺_→NH₄⁺
	NH₄⁺ assimilation	NH₄⁺+C₆H₁₂O₆+1.5O_2→C₅H₈NO₄^–+CO₂+3H₂O+2H+
NO₃^–	NO₃^– transport	NO₃^–_(out)+H⁺_(out)→ NO₃^–+1H+
	NO₃^– reduction	NO₃^–+2/3C₆H₁₂O₆+ 2O₂+2H⁺_→ NH₄⁺+4CO₂+3H₂O
	NH₄⁺ assimilation	NH₄⁺+C₆H₁₂O₆+1.5O_2→C₅H₈NO₄^–+CO₂+3H₂O+2H+

H⁺, H⁺ production and H⁺, H⁺ consumption in the cytoplasm. In the process of NH₄⁺ transport, it is assumed that 1NH₄⁺ counterbalances 1 extra H⁺, released to outside the cell (out). In the process of NH₄⁺ assimilation, if the glucose is ample, 2H⁺ will be produced in the cytoplasm. For 1NO₃^–/2H⁺ co-transport into the cytoplasm, it is assumed that 1H⁺ is pumped out of the cell by the PM H⁺-ATPase. For NO₃^– reduction, 2H⁺ will be produced when plenty of carbon is available. Combining the NO₃^– transport, reduction, and assimilation, if 1NO₃^– is totally incorporated into 1 glutamate (Glu), it yields 1H⁺ in the cell, and 1H⁺ extra (Britto and Kronzucker, 2005). If 1NH₄⁺ is transported and assimilated to 1Glu, it generates 1H⁺ in the cell, and 1H⁺ extra (Britto and Kronzucker, 2005).