Potential Pathway of Nitrous Oxide Formation in Plants

• Published in: Frontiers in plant science Vol. 11; p. 1177
• Main Authors: Timilsina, Arbindra, Zhang, Chuang, Pandey, Bikram, Bizimana, Fiston, Dong, Wenxu, Hu, Chunsheng
• Format: Journal Article
• Language: English
• Published: Frontiers Media S.A 31-07-2020
• Subjects: anoxia; hypoxia; nitrate; nitric oxide; nitrite; nitrous oxide; Plant Science
• ISSN: 1664-462X; 1664-462X
• DOI: 10.3389/fpls.2020.01177

Plants can produce and emit nitrous oxide (N
2
O), a potent greenhouse gas, into the atmosphere, and several field-based studies have concluded that this gas is emitted at substantial amounts. However, the exact mechanisms of N
2
O production in plant cells are unknown. Several studies have hypothesised that plants might act as a medium to transport N
2
O produced by soil-inhabiting microorganisms. Contrarily, aseptically grown plants and axenic algal cells supplied with nitrate (NO
3
) are reported to emit N
2
O, indicating that it is produced inside plant cells by some unknown physiological phenomena. In this study, the possible sites, mechanisms, and enzymes involved in N
2
O production in plant cells are discussed. Based on the experimental evidence from various studies, we determined that N
2
O can be produced from nitric oxide (NO) in the mitochondria of plants. NO, a signaling molecule, is produced through oxidative and reductive pathways in eukaryotic cells. During hypoxia and anoxia, NO
3
in the cytosol is metabolised to produce nitrite (NO
2
), which is reduced to form NO
via
the reductive pathway in the mitochondria. Under low oxygen condition, NO formed in the mitochondria is further reduced to N
2
O by the reduced form of cytochrome c oxidase (CcO). This pathway is active only when cells experience hypoxia or anoxia, and it may be involved in N
2
O formation in plants and soil-dwelling animals, as reported previously by several studies. NO can be toxic at a high concentration. Therefore, the reduction of NO to N
2
O in the mitochondria might protect the integrity of the mitochondria, and thus, protect the cell from the toxicity of NO accumulation under hypoxia and anoxia. As NO
3
is a major source of nitrogen for plants and all plants may experience hypoxic and anoxic conditions owing to soil environmental factors, a significant global biogenic source of N
2
O may be its formation in plants
via
the proposed pathway.