Activities of oxidoreductase enzymes in tissue extracts and sterile root exudates of three crop plants, and some properties of the peroxidase component

Abstract

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.

Responses of bioenergy sorghum cell wall metabolism to agronomic practices

“…Most of the inactive isoenzymes were acidic (pI < 4.0), and the active isoenzymes (boxed) had higher pI values. Chromatographic and two-dimensional purification procedures had been inadequate for concentrating the active isoenzymes, and removing them from the inactive forms [23][24][25]. Native polyacrylamide gel electrophoresis (PAGE) of the Rotofor fractions revealed the two groups (anionic and cationic) of isoenzymes that make up the charge isomers (Figures 1-4).…”

“…Rotofor IEF separated the isoenzyme population into 9 -15 charge isomers similar to other peroxidases [23]. Isoelectric focusing arranged the isoenzymes in three groups: negatively charged, neutral, and mildly alkaline isoenzymes (Figures 1-4).…”

Plant host habitat and root exudates shape soil bacterial community structure

“…These results emphasize the importance of the indirect impact of the rhizosphere in the turnover of SOM. Moreover, roots of certain plants release exoenzymes and organic acids, which contribute to SOM degradation (Gramss and Rudeschko, 1998;Kuzyakov, 2002;Kumar et al, 2006). Therefore, plants with well-developed and branched root system might accelerate SOM decomposition (Kuzyakov, 2002) and consequently provide organic substrates for microbial communities.…”

Formation of the Azodication (ABTS2+) from ABTS [2,2′-Azinobis-(3-ethylbenzothiazoline-6-sulphonate)] in Sterile Plant Cultures: Root–Exuded Oxidoreductases Contribute to Rhizosphere Priming

“…Thereby, the mode of P or P/Fe(II) starvation was retained to increase the root exudation of malate/malonate [55]. Applications of Mn(II) were also withheld that could lead to the formation of the abiotic Mn 3+ catalyst [58] by plant PO/root phenolic mediator systems [32,38]. Supplements of 50 mg autoclaved pyrolusite (MnO 2 , Merck) in oxide activated or in the more passive powdered stage were used to serve as active-oxygen independent abiotic catalysts [45].…”

“…Soil-grown alfalfa plants (40 d old) contained 42 mg kg −1 DW of peroxide in the shoot, and traces in root tissue and in aseptic root exudates [38]. With its content of up to 30% phenolic units [39], the humus polymer matches with the substrate spectrum of laccases, peroxidases, and abiotically generated oxidants such as hydroxyl radical (HO • ) that is reduced to water upon H + /e -abstractions from organics (E 0 = 1.8-2.7 V) [40].…”