Absorption and metabolism of formaldehyde in solutions by detached banana leaves

14-3-3 proteins regulate the HCHO stress response by interacting with AtMDH1 and AtGS1 in tobacco and Arabidopsis

Formaldehyde (HCHO) is one of the most essential common carcinogenic environmental pollutants. While 14-3-3 proteins are known to regulate the response of plants to HCHO stress, the regulatory mechanisms responsible for a tolerant phenotype remain unclear. We first performed qPCR analysis of HCHO-treated Arabidopsis and tobacco and determined that the expression of At14-3-3PSI and Nt14-3-3C genes was rapidly upregulated after HCHO stress. Furthermore, overexpression of 14-3-3, AtMDH1 or AtGS1 genes enhanced plant HCHO absorption capacity and resistance, and knockdown or knockout of 14-3-3, AtMDH1 or AtGS1 genes reduced plant HCHO absorption capacity and resistance. However, overexpression of the AtGS1 and AtMDH1 genes in the At14-3-3 psi mutant restored HCHO uptake and resistance in Arabidopsis. Moreover, 14-3-3 bound to the N-terminus of AtMDH1 and the C-terminus of AtGS1, respectively, and repressed and enhanced their expression. The ¹³C NMR results of HCHO stress mutants Atgs1 and Atmdh1 showed that the metabolites Glu and Asp rapidly increased, indicating that AtGS1 and AtMDH1 were indeed indispensable for Arabidopsis to metabolize HCHO. In conclusion, we uncovered a HCHO stress response mechanism mediated by 14-3-3, which enhances the plant's ability to absorb HCHO, deepening our understanding of how plants respond to HCHO stress.

New Insight into Short Time Exogenous Formaldehyde Application Mediated Changes in Chlorophytum comosum L. (Spider Plant) Cellular Metabolism

Chlorophytum comosum L. plants are known to effectively absorb air pollutants, including formaldehyde (HCHO). Since the metabolic and defense responses of C. comosum to HCHO are poorly understood, in the present study, biochemical changes in C. comosum leaves induced by 48 h exposure to exogenous HCHO, applied as 20 mg m^-3, were analyzed. The observed changes showed that HCHO treatment caused no visible harmful effects on C. comosum leaves and seemed to be effectively metabolized by this plant. HCHO application caused no changes in total chlorophyll (Chl) and Chl a content, increased Chl a/b ratio, and decreased Chl b and carotenoid content. HCHO treatment affected sugar metabolism, towards the utilization of sucrose and synthesis or accumulation of glucose, and decreased activities of aspartate and alanine aminotransferases, suggesting that these enzymes do not play any pivotal role in amino acid transformations during HCHO assimilation. The total phenolic content in leaf tissues did not change in comparison to the untreated plants. The obtained results suggest that HCHO affects nitrogen and carbohydrate metabolism, effectively influencing photosynthesis, shortly after plant exposure to this volatile compound. It may be suggested that the observed changes are related to early HCHO stress symptoms or an early step of the adaptation of cells to HCHO treatment. The presented results confirm for the first time the direct influence of short time HCHO exposure on the studied parameters in the C. comosum plant leaf tissues.

A rapid method to assess the formaldehyde dehydrogenase activity in plants for the remediation of formaldehyde

The formaldehyde dehydrogenase (FADH) activity in plants is essential to the removal of airborne formaldehyde (FA) by plants. A rapid and efficient method was established to assess the FADH activity in plants by analyzing the efficiencies of the extracts of fresh and enzyme-inactivated leaves to degrade FA, with the enzyme-inactivated leaves prepared by freezing with liquid nitrogen. The efficiencies of airborne FA dissipated by different plants were evaluated through the FA fumigation experiments using four selected plants, with the results analyzed against the calculated leaf FADH activities. Fresh and enzyme-inactivated leaf extracts degraded FA to different extents. The degradative efficiencies of leaf extracts were positively related to the initial FA test levels at 6-18 mg l^-1. The relative plant-leaf FADH activities formed the order of Chenopodium album L. > Atenia cordifolia > Plantain > Aloe, which was in line with the observed FA dissipating efficiencies of the plants exposed to 0.72 mg m^-3 airborne FA for 24 h. Other dominant degrading mechanisms in plant leaves resulted in higher dissipating efficiencies of Plantain over that of Atenia cordifolia when exposed to 1.56 mg m^-3 FA for 24 h. The established method could be applied to estimate the FADH activity in plants for assessment of the plant remediation efficiency of FA in air at lower concentrations.

Formaldehyde assimilation through coordination of the glyoxylate pathway and the tricarboxylic acid cycle in broad bean roots

Formaldehyde (HCHO) assimilation in broad bean (Vicia faba L. cv. YD) roots was investigated using ¹³C-labeled HCHO followed by ¹³C-NMR analysis. Results revealed that H¹³CHO was first oxidized to H¹³COOH in the roots treated with 2 mM H¹³CHO in a time-dependent manner. Subsequently, a massive signal peak of [2, 4-¹³C]citrate (Cit) and a signal peak of [2, 3-¹³C]succinate (Su) were observed in accompany with an enhancement in the signal intensity of [3-¹³C]Cit. The data suggested that the glyoxylate pathway and the tricarboxylic acid (TCA) cycle functioned simultaneously in the subsequent assimilation of H¹³COOH. The yield of [2, 4-¹³C]Cit accounted for more than 80% of the total metabolites. The activity of isocitrate lyase (ICL), a key enzyme in the glyoxylate pathway, was stimulated by HCHO in a dosage-dependent manner. As a result, [2, 4-¹³C]Cit production was increased significantly in YD roots treated with high concentrations (4 and 6 mM) of H¹³CHO. Moreover, induction of the ICL activity by methanol resulted in a simultaneous elevation in the production of [2, 4-¹³C]Cit and [3-¹³C]Cit in methanol-pretreated roots under 2 mM H¹³CHO stress. Pretreatment of roots with cyclosporin A, which hinders the transport of ¹³C-enriched compounds into mitochondria, caused a notable decline in the signal peak and yield of [2, 4-¹³C]Cit and consequently induced a notable accumulation of [2, 3-¹³C]Su and an increase in the HCO₃^- production (generated from H¹³COOH oxidation) in H¹³CHO-treated roots. These results suggested that the glyoxylate pathway and the TCA cycle function coordinately in HCHO assimilation in broad bean roots.

Over-expression of the Arabidopsis formate dehydrogenase in chloroplasts enhances formaldehyde uptake and metabolism in transgenic tobacco leaves

MAIN CONCLUSION

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 CO2, 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. 13C-NMR analysis showed that the carbon flux from H13CHO 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 [4-13C]Asn, [3-13C]Gln, [U-13C]oxalate, and H13COOH were notably greater in transgenic leaves than in non-transformed leaves after treatment with H13CHO. 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.

Methanol-enhanced removal and metabolic conversion of formaldehyde by a black soybean from formaldehyde solutions

Methanol regulation of some biochemical and physiological characteristics in plants has been documented in several references. This study showed that the pretreatment of methanol with an appropriate concentration could stimulate the HCHO uptake by black soybean (BS) plants. The process of methanol-stimulated HCHO uptake by BS plants was optimized using the Central Composite Design and response surface methodology for the three variables, methanol concentration, HCHO concentration, and treatment time. Under optimized conditions, the best stimulation effect of methanol on HCHO uptake was obtained. 13C-NMR analysis indicated that the H13CHO metabolism produced H13COOH, [2-13C]Gly, and [3-13C]Ser in BS plant roots. Methanol pretreatment enhanced the metabolic conversion of H13CHO in BS plant roots, which consequently increased HCHO uptake by BS plants. Therefore, methanol pretreatment might be used to increase HCHO uptake by plants in the phytoremediation of HCHO-polluted solutions.

Investigation of the role of the calvin cycle and C1 metabolism during HCHO metabolism in gaseous HCHO-treated petunia under light and dark conditions using 13C-NMR

INTRODUCTION

It has been shown that formaldehyde (HCHO) absorbed by plants can be assimilated through the Calvin cycle or C1 metabolism. Our previous study indicated that Petunia hybrida could effectively eliminate HCHO from HCHO-polluted air.

OBJECTIVE

To understand the roles of C1 metabolism and the Calvin cycle during HCHO metabolism and detoxification in petunia plants treated with gaseous H(13)CHO under light and dark conditions.

METHODS

Aseptically grown petunia plants were treated with gaseous H(13)CHO under dark and light conditions. The metabolites generated from HCHO detoxification in petunia were investigated using (13)C-NMR.

RESULTS

[2-(13)C]glycine (Gly) was generated via C1 metabolism and [U-(13)C]glucose (Gluc) was produced through the Calvin cycle simultaneously in petunia treated with low-level gaseous H(13)CHO under light conditions. Generation of [2-(13)C]Gly decreased whereas [U-(13) C]Gluc and [U-(13)C]fructose (Fruc) production increased greatly under high-level gaseous H(13)CHO stress in the light. In contrast, [U-(13)C]Gluc and [U-(13)C] Fruc production decreased greatly and [2-(13)C]Gly generation increased significantly under low-level and high-level gaseous H(13)CHO stress in the dark.

CONCLUSION

C1 metabolism and the Calvin cycle contributed differently to HCHO metabolism and detoxification in gaseous H(13CHO-treated petunia plants. As the level of gaseous HCHO increased, the role of C1 metabolism decreased and the role of the Calvin cycle increased under light conditions. However, opposite changes were observed in petunia plants under dark conditions.