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Fig. 7 in Rosmarinic acid and hesperidin regulate gas exchange, chlorophyll fluorescence, antioxidant system and the fatty acid biosynthesis-related gene expression in Arabidopsis thaliana under heat stress

Fig. 7. The changes of monodehydroascorbate reductase activity (MDHAR, A), dehydroascorbate reductase activity (DHAR, B), ascorbate content (AsA, C), dehydroascorbate content (DHA, D), glutathione content (GSH, E), oxidized glutathione content (GSSG, F), AsA/DHA (G), GSH/GSSG (H) and GSH redox state (I) after rosmarinic acid (RA, 100 μM) and/or hesperidin (HP, 100 μM) with/without heat stress (38 ◦C) in A. thaliana leaves.

Fig. 4 in Rosmarinic acid and hesperidin regulate gas exchange, chlorophyll fluorescence, antioxidant system and the fatty acid biosynthesis-related gene expression in Arabidopsis thaliana under heat stress

Fig. 4. The changes of the relative band intensity of different types of peroxidase isoenzymes (POX, A) and POX activity (B), relative band intensity of different types of NADPH oxidase isoenzymes (NOX, C) and NOX activity (D) after rosmarinic acid (RA, 100 μM) and/or hesperidin (HP, 100 μM) with/without heat stress (38 ◦C) in A. thaliana leaves.

Fig. 3 in Rosmarinic acid and hesperidin regulate gas exchange, chlorophyll fluorescence, antioxidant system and the fatty acid biosynthesis-related gene expression in Arabidopsis thaliana under heat stress

Fig. 3. The changes of the relative band intensity of different types of superoxide dismutase isoenzymes (SOD, A) and SOD activity (B), the relative band intensity of different types of catalase isoenzymes (CAT, C) and CAT activity (D) after rosmarinic acid (RA, 100 μM) and/or hesperidin (HP, 100 μM) with/without heat stress (38 ◦C) in A. thaliana leaves.

Fig. 2 in Rosmarinic acid and hesperidin regulate gas exchange, chlorophyll fluorescence, antioxidant system and the fatty acid biosynthesis-related gene expression in Arabidopsis thaliana under heat stress

Fig. 2. The changes of hydrogen peroxide content (H O, A), lipid peroxidation (TBARS content, B), histochemical staining for O • accumulation (C), histochemical 2 2 2 staining for H2O2 determination (D), histochemical staining for plasma membrane integrity (E) and histochemical staining for lipid peroxidation (F) after rosmarinic acid (RA, 100 μM) and/or hesperidin (HP, 100 μM) with/without heat stress (38 ◦C) in A. thaliana leaves.

Fig. 6 in Rosmarinic acid and hesperidin regulate gas exchange, chlorophyll fluorescence, antioxidant system and the fatty acid biosynthesis-related gene expression in Arabidopsis thaliana under heat stress

Fig. 6. The changes of the relative band intensity of different types of ascorbate glutathione isoenzymes (APX, A) and APX activity (B), and glutathione reductase activity (GR, C) after rosmarinic acid (RA, 100 μM) and/or hesperidin (HP, 100 μM) with/without heat stress (38 ◦C) in A. thaliana leaves.

Fig. 59 in The scope of flavin-dependent reactions and processes in the model plant Arabidopsis thaliana

Fig. 59. Putative reaction catalyzed by HTH (HOTHEAD). Shown are the successive oxidations of the ω-hydroxyl group to the aldehyde and eventually, to the carboxy-group, leading to an α,ω-dicarboxylic acid. Members of the GMC oxidoreductases typically react readily with dioxygen to produce hydrogen peroxide.

Fig. 57 in The scope of flavin-dependent reactions and processes in the model plant Arabidopsis thaliana

Fig. 57. Reaction catalyzed by DNA-photolyases. The excited state reduced FAD is generated via activation by an additional antenna chromophore (top). In the case of CRY3 N5,N10-methenyltetrahydrofolate was shown to act as the antenna chromophore (G¨obel et al., 2017). During the repair reaction the reduced FAD returns to the ground state and requires re-activation by the antenna chromophore for the next reaction cycle. While the redox state of the flavin cofactor does not change in the overall reaction, intermediate transfer or electrons is critical for the reaction mechanism (see text).

Fig. 56 in The scope of flavin-dependent reactions and processes in the model plant Arabidopsis thaliana

Fig. 56. The oxidation of glycolate catalyzed by glycolate oxidase. Glycolate, the shortest substrate of the family of 2-hydroxy acid oxidases, is oxidized to glyoxylate in the peroxisomes. The members of the family feature different chain-length specificities (see text for further details). The reduced FMN is reoxidized by dioxygen yielding hydrogen peroxide.

Fig. 58 in The scope of flavin-dependent reactions and processes in the model plant Arabidopsis thaliana

Fig. 58. Flavoenzymes involved in the generation of ROS in A. thaliana. A total of 68 flavin-dependent enzymes were found to be involved in the formation of ROS in A. thaliana, either as hydrogen peroxide or superoxide radical (dark blue, taken from Table 1). Out of these 68, 48 enzymes were predicted to be present in a single cellular compartment, 19 were in at least two and one enzyme was predicted in at least three cellular compartments. The enzymes are ubiquitously distributed across the different cellular compartments (AP, apoplast = 19; PX, peroxisome = 15; PM, plasma membrane = 12; M, mitochondria = 11; Cyto, cytosol = 12; CP, chloroplast = 10; N, nucleus = 4; G, Golgi and EX, extracellular region = 2 and ER, endoplasmic reticulum = 1 enzyme). The predicted ROS producing flavoproteins from Table 5 are shown in light blue. Out of 18, 13 enzymes were predicted to be present in a single cellular compartment and 5 were predicted to be present at least in two. (PM = 2; M = 1; Cyto = 2; CP = 10; N = 3; EX = 2, EMS, endomembrane system = 1 and ER = 2). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 53 in The scope of flavin-dependent reactions and processes in the model plant Arabidopsis thaliana

Fig. 53. Mechanism of action of quiescin sulfhydryl oxidase. The enzyme possesses two pairs of cysteines (see text) of which only the proximal pair is shown in the figure. In the resting state, the two proximal cysteines form an intramolecular disulfide that is reduced via interaction with the reduced dithiol of the thioredoxin domain. The reduced proximal dithiol then reduces the FAD, which is reoxidized by dioxygen.

Fig. 54 in The scope of flavin-dependent reactions and processes in the model plant Arabidopsis thaliana

Fig. 54. Mechanism of Erv and Ero as partners for protein disulfide isomerase. In contrast to quiescin sulfhydryl oxidase, Erv and Ero do not interact directly with client proteins but serve to keep protein disulfide isomerase in an active oxidized state in order to allow for the proper generation of disulfide bonds in client proteins. Reduced Erv and Ero are reoxidized by dioxygen giving rise to the production of hydrogen peroxide.

Fig. 52 in The scope of flavin-dependent reactions and processes in the model plant Arabidopsis thaliana

Fig. 52. Reaction of glutathione reductase with its cognate substrate glutathione. Glutathione reductase is primed by reduction at the expense of NADPH generating the reduced FAD, which subsequently reduces the internal disulfide bond. Next, oxidized glutathione (GSSG) is cleaved to two molecules of (reduced) glutathione (GSH) by a dithiol-disulfide exchange reaction. For a detailed mechanistic discussion see Miller (2013).

Fig. 51 in The scope of flavin-dependent reactions and processes in the model plant Arabidopsis thaliana

Fig. 51. Proposed reaction mechanism of lysine-specific histone demethylase. The oxidation of a methylated lysine residue (typically in position 4 of histone 3) is shown. Initially, oxidation of the substrate generates reduced FAD, which is re-oxidized by dioxygen leading to the production of hydrogen peroxide. The intermediate imine is hydrolyzed by water to produce the final products, the demethylated lysine side chain and formaldehyde (see also reaction of sarcosine oxidase).

Fig. 50 in The scope of flavin-dependent reactions and processes in the model plant Arabidopsis thaliana

Fig. 50. Reaction catalyzed by TYW1. N1-methylguanosine (m1G) in position 37 of the tRNA is converted to 4-demethylwyosine (imG-14). The two carbon atoms required to set up the tricyclic system are derived from pyruvate (Lombard and Hamdane, 2017).

Fig. 45 in The scope of flavin-dependent reactions and processes in the model plant Arabidopsis thaliana

Fig. 45. Reaction catalalyzed by quinone reductases. As an example, the reduction of benzoquinone is shown. However, quinone reductases generally have a broad substrate spectrum with regard to modifications at the aromatic ring. The source of electrons is typically NAD(P)H.

Fig. 41 in The scope of flavin-dependent reactions and processes in the model plant Arabidopsis thaliana

Fig. 41. Reaction catalyzed by cellodextrin oxidase (AtBBE22/CELLOX). This enzyme oxidizes the reducing end of oligosaccharides with a preference to chains with n = 1–4 (Locci et al., 2019). Based on the analysis of the oxygen reactivity motif, all reduced cellodextrin oxidases are predicted to react with dioxygen to yield hydrogen peroxide (Zafred et al., 2015) (see also discussion below).

Fig. 49 in The scope of flavin-dependent reactions and processes in the model plant Arabidopsis thaliana

Fig. 49. Reactions catalyzed by tRNA-dihydrouridine synthase (DUS) and the MnmE/MnmG (GidA) complex. (Top) Reduction of tRNA-uridine by tRNA-dihydrouridine synthase. The reduced FMN is generated at the expense of NADH. (Bottom) The modification of tRNA-uridine by the MmnEG complex requires GTP and methylenetetrahydrofolate (MTHF). The latter provides the carbon atom that is directly transferred to the 5′-position of the pryrimidine ring. Depending on whether ammonia or glycine is used as a co-substrate either nm5U or cmnm5U are generated. For more details on the reaction mechanism see text and Moukadiri et al. (2009).

Fig. 46 in The scope of flavin-dependent reactions and processes in the model plant Arabidopsis thaliana

Fig. 46). The ten genes encoding RBOHs in A. thaliana exhibit distinct expression patterns and exert special roles in various processes ranging from immune responses to plant development (for a review see Smirnoff and Arnaud, 2019). For example, RBOHD was shown to participate in wound response and systemic signaling (Miller et al., 2009) and RBOHD/F is involved in stomatal function and pathogen defense

Fig. 40 in The scope of flavin-dependent reactions and processes in the model plant Arabidopsis thaliana

Fig. 40. Reaction catalyzed by oligogalacturonide oxidase (AtBBE20). This enzyme specifically oxidizes oligogalacturonides with similar activities found for a chain length of n = 2 to n = 12 (Benedetti et al., 2018). Based on the analysis of the oxygen reactivity motif, all reduced oligogalacturonide oxidases are predicted to react with dioxygen to yield hydrogen peroxide (Zafred et al., 2015).

Fig. 36 in The scope of flavin-dependent reactions and processes in the model plant Arabidopsis thaliana

Fig. 36. Putative mechanism of isomerization followed by reduction. Isomerization is initiated by hydride transfer resulting in the removal of a deuteride from the (25)-carbon. This deuteride may be accepted by the flavin cofactor in exchange to the hydride provided in the initial step. Since the hydrogens of the reduced FAD cofactor are prone to exchange with solvent-borne hydrogens the reduction of the double bond will occur by transfer of a hydride