Assimilation and metabolism of formaldehyde by leaves appear unlikely to be of value for indoor air purification

Abstract

Uptake, translocation and metabolism of ¹⁴C-labelled formaldehyde in the leaves of Epipremnum aureum (Golden Potho) and Ficus benjamina (Weeping Fig) were investigated. Plants were exposed in light and dark to ¹⁴C-formaldehyde (500 μg m⁻³) in gas exposure chambers. The amount of ¹⁴C-incorporation into the soluble (water-extractable) and insoluble fractions of leaves, stem sections and roots was determined. The soluble ¹⁴C-activity was fractionated by ion exchange chromatography followed by thin-layer chromatography/autoradiography. Approximately 60–70% of the applied ¹⁴C-formaldehyde was recovered from the plants. In the light about five times more ¹⁴C-formaldehyde was assimilated than in the dark. The amount of ¹⁴C-label derived from ¹⁴C-formaldehyde, which was incorporated into acid-stable metabolites, was enhanced to an even larger extent in the light. The ¹⁴C-activity pattern closely resembled the general labelling spectrum of photosynthates, obtained after a ¹⁴CO₂ exposure. A substantial amount of labelled material, mostly sucrose, was translocated into the stems and roots. Our results suggest that in the light ¹⁴C enters the Calvin cycle after an enzymatic two-step oxidation process of ¹⁴C-formaldehyde to ¹⁴CO₂. The activities of the respective enzymes, formaldehyde dehydrogenase and formate dehydrogenase, were determined. Among 27 ‘leafy’ indoor decorative plants, a screening experiment revealed no outstanding species with regard to its capacity for metabolism of formaldehyde, and rate of uptake through stomata was too low to justify claims that plants contribute usefully to indoor air purification.