Over-expression of AtFDH controlled by the promoter of Rubisco small subunit in chloroplasts increases formaldehyde uptake and metabolism in tobacco leaves. Our previous study showed that formaldehyde (HCHO) uptake and resistance in tobacco are weaker than in Arabidopsis. Formate dehydrogenase in Arabidopsis (AtFDH) is a key enzyme in HCHO metabolism by oxidation of HCOOH to CO, which enters the Calvin cycle to be assimilated into glucose. HCHO metabolic mechanism in tobacco differs from that in Arabidopsis. In this study, AtFDH was over-expressed in the chloroplasts of transgenic tobacco using a light inducible promoter. C-NMR analysis showed that the carbon flux from HCHO metabolism was not introduced into the Calvin cycle to produce glucose in transgenic tobacco leaves. However, the over-expression of AtFDH significantly enhanced the HCHO metabolism in transgenic leaves. Consequently, the productions of [4-C]Asn, [3-C]Gln, [U-C]oxalate, and HCOOH were notably greater in transgenic leaves than in non-transformed leaves after treatment with HCHO. The increased stomatal conductance and aperture in transgenic leaves might be ascribed to the increased yield of oxalate in the guard cells with over-expressed AtFDH in chloroplasts. Accordingly, the transgenic plants exhibited a stronger capacity to absorb gaseous HCHO. Furthermore, the higher proline content in transgenic leaves compared with non-transformed leaves under HCHO stress might be attributable to the excess formate accumulation and Gln production. Consequently, the HCHO-induced oxidative stress was reduced in transgenic leaves.

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