A novel formaldehyde metabolic pathway plays an important role during formaldehyde metabolism and detoxification in tobacco leaves under liquid formaldehyde stress

• HCHO uptake by tobacco leaves and treatment time exhibits a linear function.
• A novel HCHO metabolic pathway is detected in HCHO-treated tobacco leaves.
• HCHO metabolism produces [4-13C]Asn, [3-13C]Gln and [U-13C]OA via the novel pathway.
• CSA and dark pretreatment completely inhibits the role of the novel metabolic pathway.
• This novel metabolic pathway plays an important during HCHO uptake in tobacco leaves.

Tobacco and Arabidopsis are two model plants often used in botany research. Our previous study indicated that the formaldehyde (HCHO) uptake and assimilation capacities of tobacco leaves were weaker than those of Arabidopsis leaves. After treatment with a 2, 4 or 6 mM HCHO solution for 24 h, detached tobacco leaves absorbed approximately 40% of the HCHO from the treatment solution. 13C-NMR analysis detected a novel HCHO metabolic pathway in 2 mM H13CHO-treated tobacco leaves. [4-13C]Asn, [3-13C]Gln and [U-13C]oxalic acid (OA) were produced from this pathway after H13COOH generation during H13CHO metabolism in tobacco leaves. Pretreatments of cyclosporin A (CSA) and dark almost completely inhibited the generation of [4-13C]Asn, [3-13C]Gln and [U-13C]OA from this pathway but did not suppressed the production of H13COOH in 2 mM H13CHO-treated tobacco leaves. The evidence suggests that this novel pathway has an important role during the metabolic detoxification of HCHO in tobacco leaves. The analysis of the chlorophyll and Rubisco contents indicated that CSA and dark pretreatments did not severely affect the survival of leaf cells but significantly inhibited the HCHO uptake by tobacco leaves. Based on the effects of CSA and dark pretreatments on HCHO uptake and metabolism, it is estimated that the contribution of this novel metabolic pathway to HCHO uptake is approximately 60%. The data obtained from the 13C-NMR analysis revealed the mechanism underlying the weaker HCHO uptake and assimilation of tobacco leaves compared to Arabidopsis leaves.