The Studies On Formaldehyde Metabolic Mechanism In Petunia Hybrida And The Genetic Manipulation For Enhancing Its Formaldehyde Phytoremediation Ability

Formaldehyde (HCHO) is one of the main indoor air pollutants. Ornamental plants are considered to be the best choice to remove indoor HCHO, but their HCHO-absorption and-metabolism ability is greatly limited. Studies have shown that genetic engineering can effectively enhance the ability of the plant HCHO-uptake and-detoxification capacity.It has been demonstrated that plants have the ability of HCHO-absorption and-metabolism. But the formaldehyde metabolic pathways in plants is unclear. Some study suggested that the HCHO was detoxified in one-carbon (C1) metabolism after absorbed by plants. The research of the plant formaldehyde metabolism not only can provide a scientific basis for the use of phytoremediation formaldehyde pollution strategies, but also can provide more genetic resources to improve plant HCHO-metabolic capacity. Petunia is a representative of the ornamental plants, it can fast-growing, short cycle, transplanting easy to survive, but also has practical value. The genetic background of the Petunia hybrida have also been extensive and in-depth study, the genetic information is more likely to get. In this study, analysised the H13CHO metabolic pathway in Petunia hybrida under H13CHO stress. Under both liquids and gases H13CHO stress, the absorbed H13CHO was firstly oxidized as H13COOH through the glutathione-dependent HCHO dehydrogenase (FALDH) pathway. A part of the H13COOH was oxidized subsequently by formate dehydrogenase (FDH) as13CO2, which was incorporated into Calvin Cycle to generate [U-13C]glucose (Glc). We found under low-level liquid (2mM) H13CHO stress have a different H13CHO metabolic pathway, a part of H13COOH converted to5-13CH2-THF by the10-Formyl-THF synthetase (FTS), and then converted to [5-13C]-Met with Homocysteine. H13CHO also might directly bound with THF to form the5,10-13CH2-THF adduct, which was quickly used to produce [5-13C]-Met. This pathway is the methylation cycle in the C1metabolic networks. Under high-level (4-6mM) liquid and gas H13CHO stress also have a different pathway, a part of H13COOH formed13C-Glyoxylate by glyoxylic acid synthase, then converted to [2-13C]-Gly by glyoxylate aminotransferase. This pathway has been confirmed in potato. To prove the above hypothesis, this study also analyzed various physiological characteristics of Petunia hybrida under formaldehyde stress, hydrogen peroxide and malondialdehyde content significantly increased, shows that Petunia hybrida had a severe oxidative damage, and the extent of lipid oxidation is more obvious. Carbonyl protein content also rose, but the rise is smaller, indicating that the extent of protein damage is smaller. Formaldehyde stress also lead to decreased of chlorophyll content in Petunia hybrida;which may affect the photosynthesis, thereby affecting the formaldehyde metabolism in Petunia hybrida. Soluble sugar content of the trend is different in Liquid and gaseous formaldehyde treatment. In liquid formaldehyde treatment,the content of Soluble sugar decreased,whith was caused by Flooding stress.But In gas formaldehyde treatment, the content of Soluble sugar rose. Waterlogging stress affected the formaldehyde metabolic pathways in Petunia hybrida,there are different ormaldehyde metabolic pathways under liquid and gas formaldehyde stress.Through the above research, We hypothesized that the formate dehydrogenase (FDH) is a key enzyme, may influence the HCHO metabolism of Petunia hybrida. Arabidopsis FDH has been purified and identified, which have been proved to target chloroplasts as well as mitochondria, and more active in the chloroplast. That enhanced HCHO metabolize in Arabidopsis.Because in Arabidopsis.more of H13COOH was oxidized by formate dehydrogenase (FDH) as13CO2, and which was incorporated into Calvin Cycle to generate [U-13C]glucose (Glc) more quickly. In this study,the atfdh gene was transformed into Petunia hybrida, and obtained overexpression atfdh gene of transgenic Petunia hybrida. The study proved that transgenic Petunia hybrida can absorption more of exogenous formaldehyde. Physiological levels of analysis showed that the transgenic Petunia hybrida can tolerated higher concentrations of HCHO stress.13C-NMR analysis showed that in transgenic plants more of H13COOH was oxidized by formate dehydrogenase (FDH) as13CO2, and which was incorporated into Calvin Cycle to generate [U-13C] glucose (Glc) more quickly. The [U-13C]Gluc was fluxed into glycolysis pathway and the TCA cycle to generate carbon skeletons of nitrogen-transport amino acids (Ser, Gly and Arg). Therefore, the The successful construction of transgenic Petunia hybrida provided a quick and efficient approach for molecular breeding to generate the functional ornamental plants which can be applied to phytoremediation of HCHO pollution.