“…It would appear then that manganese plays an important part in oxidation. Apart from the studies of Kenten and Mann (19), however, no mechanism of oxidative metabolism involving manganese has been suggested.…”
Section: Discussionmentioning
confidence: 99%
“…They find an inverse relationship between peroxidase on the one hand and catalase and chlorophyll on the other. Schwarze (26) (19) have found catalase to be inhibitory to the peroxidase-manganese oxidizing system. Some participation of peroxidase in terminal oxidation cannot, therefore, be excluded.…”
“…It would appear then that manganese plays an important part in oxidation. Apart from the studies of Kenten and Mann (19), however, no mechanism of oxidative metabolism involving manganese has been suggested.…”
Section: Discussionmentioning
confidence: 99%
“…They find an inverse relationship between peroxidase on the one hand and catalase and chlorophyll on the other. Schwarze (26) (19) have found catalase to be inhibitory to the peroxidase-manganese oxidizing system. Some participation of peroxidase in terminal oxidation cannot, therefore, be excluded.…”
“…Already Kenten and Mann (1950) detected a significant influence of several phenolic compounds on the POD-catalyzed oxidation of manganous pyrophosphate. Mn oxidation was stimulated by monohydroxy phenols but not by dihydroxy and trihydroxy phenols.…”
Section: The Effect Of Cofactors On Nadh-peroxidase Activitymentioning
The apoplast is considered the leaf compartment decisive for manganese (Mn) toxicity and tolerance in cowpea (Vigna unguiculata). Particularly apoplastic peroxidases (PODs) were proposed to be key enzymes in Mn toxicity-induced processes. The presented work focuses on the characterization of the role of hydrogen peroxide (H 2 O 2 )-producing (NADH peroxidase) and H 2 O 2 -consuming peroxidase (guaiacol POD) in the apoplastic washing fluid (AWF) of leaves for early stages of Mn toxicity and genotypic differences in Mn tolerance of cowpea. Leaf AWF of the Mn-sensitive cultivar (cv) TVu 91 but not of the Mntolerant cv 1987 showed an increase of guaiacol-POD and NADH-peroxidase activities at elevated AWF Mn concentrations. two-dimensional resolutions of AWF proteins revealed that cv TVu 91 expressed more and additional proteins at high Mn treatment, whereas Mn-tolerant cv TVu 1987 remained nearly unaffected. In both cultivars, NADH-peroxidase activity and accompanied H 2 O 2 formation rate in vitro were significantly affected by Mn 21 , p-coumaric acid, and metabolites occurring in the AWF. The total phenol concentration in the AWF was indicative of advanced stages of Mn toxicity but was rather unrelated to early stages of Mn toxicity and genotypic differences in Mn tolerance. The NADH oxidation by AWF PODs was significantly delayed or enhanced in the presence of the protein-free AWF from cv TVu 1987 or cv TVu 91, respectively. High-performance liquid chromatography analysis of AWF indicates the presence of phenols in cv TVu 1987 not observed in cv TVu 91. We conclude from our studies that the H 2 O 2 -producing NADH peroxidase and its modulation by stimulating or inhibiting phenolic compounds in the leaf apoplast play a major role for Mn toxicity and Mn tolerance in cowpea.
“…n.d., not determined. Kenten & Mann (1950). Supplementation of soybean root extracts with HRP strongly indicates (P l 0n993) that Mn$ + formation in soybean plant tissue can be solely performed by peroxidase.…”
Section: Formation Of Mn$ + Chelatesmentioning
confidence: 99%
“…This enzyme owes its ligninolytic capacity to the formation of Mn$ + and has so far been studied only in fungal systems (Schomburg et al, 1994). Formation of Mn$ + can also be initiated by phenoxy and aryloxy radicals that had been formed from phenolic substrates by HRP (Kenten & Mann, 1950), laccase (Archibald & Roy, 1992), or lignin peroxidase (Popp, Kalyanaraman & Kirk, 1990). Mn$ + ions are stabilized by chelating ligands such as organic acids, pyrophosphate, and short-chain polyphosphates, and are potent oxidants of phenolic substrates and synthetic lignins (Cavalieri & Rogan, 1985 ;Archibald & Roy, 1992 ;Wariishi et al, 1992).…”
Aqueous extracts of homogenized shoot and root tissue of alfalfa (Medicago sativa L.), white mustard (Sinapis alba L.), and cress (Lepidium sativum L.), with the exudates of sterile roots of these crop plants, were examined spectrophotometrically for the activities of 20 oxidoreductase enzymes by standard procedures. In tissue extracts and root exudates, the reactions of laccase (EC 1;10;3;2), ascorbate oxidase (EC 1;10;3;3), monophenol monooxygenase (EC 1;14;18;1), and phenol 2-monooxygenase (EC 1;14;13;7) were readily detected. Of the aromatic-ring cleavage dioxygenases, those of the meta-cleavage pathway (EC 1;13;11;2 and 1;13;11;8) could also be detected. Guaiacol peroxidase (EC 1;11;1;7) was dominant in all samples. In sterile root exudates of alfalfa, this enzyme was represented by at least seven acidic isoforms. The formation of the ligninolytic Mn$ + \malonate and Mn$ + \citrate complexes from Mn# + occurred in all tissue extracts and in root exudates of alfalfa. In root extracts of soybean (Glycine max L.), the rate of Mn$ + generation correlated (P l 0n993) with the activities of endogenous plant guaiacol peroxidase and horseradish peroxidase (HRP) supplements and also with the total phenol content in tissue extracts (P l 0n984). Plant guaiacol peroxidase and purified HRP decolorized four aromatic dyes, an activity reported to be involved in ligninolysis. Although no enzymes capable of generating H # O # as a consequence of the oxidation of simple sugars, amino acids, organic acids, and aldehydes were found, traces of peroxide were detected in tissue extracts and in the root exudate of alfalfa. It is concluded that the oxidoreductases found in plant tissues also occur in root exudates of aseptic whole plants. The significance of interrelations between oxidoreductase enzymes and enzymically generated higher-valency metal ions is discussed in the context of the oxidative conversion of phenolic compounds in soil and plant tissue.
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