The Cell Wall Proteome of Marchantia polymorpha Reveals Specificities Compared to Those of Flowering Plants

Primary plant cell walls are composite extracellular structures composed of three major classes of polysaccharides (pectins, hemicelluloses, and cellulose) and of proteins. The cell wall proteins (CWPs) play multiple roles during plant development and in response to environmental stresses by remodeling the polysaccharide and protein networks and acting in signaling processes. To date, the cell wall proteome has been mostly described in flowering plants and has revealed the diversity of the CWP families. In this article, we describe the cell wall proteome of an early divergent plant, Marchantia polymorpha, a Bryophyte which belong to one of the first plant species colonizing lands. It has been possible to identify 410 different CWPs from three development stages of the haploid gametophyte and they could be classified in the same functional classes as the CWPs of flowering plants. This result underlied the ability of M. polymorpha to sustain cell wall dynamics. However, some specificities of the M. polymorpha cell wall proteome could be highlighted, in particular the importance of oxido-reductases such as class III peroxidases and polyphenol oxidases, D-mannose binding lectins, and dirigent-like proteins. These proteins families could be related to the presence of specific compounds in the M. polymorpha cell walls, like mannans or phenolics. This work paves the way for functional studies to unravel the role of CWPs during M. polymorpha development and in response to environmental cues.

Enzymatic Activities, Characteristics of Wood-Decay and Wood Substrate Specificity within Genera of Some Wood-Rotting Basidiomycetes from Cameroon and Tropical Africa

A total of 72 species of wood-rotting Basidiomycetes belonging to 40 genera, 13 families and 5 orders, were investigated in this study of which 46 for the first time as far as type of wood-rot is concerned. 61 of the 72 cause white rot (W) representing 84.72 % of the total and 11 cause brown rot (B) or just 15.27 %, confirming the predominance already known of white rot (W) on brown rot (B) as shown in other studies. Results recorded show that even though most species belonging to same genera display the same type of rot (W or B), species of some few other genera were found to rather display different types of rot (W and B) in species within the same genera. Other results show that when determining the type of wood-rot caused by some species of fungi, in case of negative (-) test using tincture of guaiac which is known as the key test to determine the type of rot, syringaldazine must also be used as a differential test before concluding whether the species is a white (W) or brown rot (B) fungus. The level of activity of tyrosinase and peroxidase shows important variations between species of some genera, whereby some species of a given genus show varying potential level (+, ++, +++, ++++) of activities of these two enzymes, whereas other species of the same genus show no sign (-) of activity of the same enzymes. Therefore, our results led to the conclusion that the presence (+, ++, +++, ++++) or absence (-) of activity of peroxidase and tyrosinase can from now onwards also be used as an enzyme linked taxonomic criteria to distinguish between species of some genera. About detection of laccases activity, if a negative (-) result occurs during detection test in a wood-rotting fungus using syringaldazine, α-naphtol must also be used as a differential test before concluding on whether the species produces laccases or not. Based on the overall results recorded in the detection of enzymes activities, it appears necessary to use, where indicated, several substrates with different chemical sensitivities to detect the existence of an enzyme and its potential activity level in a fungal species. Additionally, preliminary lists of wood-decay fungi with potentially strong (+++, ++++) capacity to produce different types of polyphenol oxidases potentially usable in paper making industries, wastewater treatment and soil remediation, are provided. With regard to the study of substrate specificity which aimed at finding out the existence or not of a specificity between polyporales and tree wood species on which they grow, the first results recorded on a limited number of trees investigated led to the preliminary conclusion that, although some few tree species may serve as hosts for only a single species of polyporales, there is rather a greater tendency of finding several species growing on different species of wood as well as the same species of wood hosting several species of polyporales. These field observations led to the remark that a much larger inventory including a greater number of tree species in various tropical ecosystems is necessary in order to come out with a final conclusion.

Effect of Rhizoctonia spp. on Polyphenol Oxidase Enzyme Activity in Alfalfa Seedling

Soil borne diseases cause significant losses on quantity and quality of many crop species annually. Rhizoctonia is a widespread and ecologically diverse soilborne fungus causing different types of diseases in many plant species including alfalfa (Medicago sativa). Rhizoctonia species have been traditionally identified based on the cell nuclear condition. Polyphenol oxidases (PPOs) are ubiquitous copper-containing enzymes that are widely occurring enzymes among plants. PPOs are involved in the oxidation of polyphenols into quinones (antimicrobial compounds) and lignification of plant cells that contribute to the formation of defense barriers against pathogens. The study was conducted with the aim to determine the effect of indigenous isolates of a multinucleate (Rhizoctonia solani AG-4) and nineteen isolates of binucleate Rhizoctonia on PPO activity in alfalfa (cv. Gea) seedling under in vitro conditions. The activity of PPO enzyme was determined in inoculated and uninoculated control alfalfa plants after ten days from inoculation. There was a significant increase in the activity of PPO after treatment of alfalfa seedling with isolates of Rhizoctonia. Among Rhizoctonia isolates, highest induction of PPO activity was recorded with pathogenic R. solani AG-4. In present study, increased amounts of PPO were also observed in plants that were challenged with Rhizoctonia spp. PPO has a role in catalyzing phenolic oxidation in limiting disease development. PPO may therefore be involved in induction of defense resistance against plant diseases.

Inhibition of enzymatic browning in fruit and vegetable, review

The second-largest cause of losing quality in vegetables and fruits (VFs) is enzymatic browning (EB). As a result of polyphenol oxidases (PPOs), EB leads to the color performance of vegetable and fruit yields. To inhibit the activity of PPOs, chemical and physical methods have been developed and several synthetic chemical compounds are widely used as Anti-Browning Agents (ABA) in VFs products. In recent times, emphasis was placed on customer-oriented food manufacturing innovations. Customers have a tendency to encourage the usage of PPO inhibitors that are natural and environmentally friendly. The aim of present review is to illustrate the underlying mechanisms of PPO chemical inhibitor anti browning action and current trends in some of these inhibitor studies. Studies developed over the last decade have been reported and discussed, such as Natural, chemical, physical, controlled atmosphere and coating techniques to avoid EB. The purpose of this review article will be to assemble and reveal an up-to-date demonstration of browning inhibiting natural and synthetic compounds. The details available in this review could also take to facilitate the ultimate objective of developing new inhibitors of enzymatic browning (plant extracts, natural and synthetic compounds) that are acceptable, healthy and beneficial for the food industry.

Molecular and Enzymatic Characterization of Flavonoid 3′-Hydroxylase of Malus × domestica

Malus × domestica (apple) accumulates particularly high amounts of dihydrochalcones in various tissues, with phloridzin (phloretin 2′-O-glucoside) being prevalent, although small amounts of 3-hydroxyphloretin and 3-hydroxyphloridzin are also constitutively present. The latter was shown to correlate with increased disease resistance of transgenic M. × domestica plants. Two types of enzymes could be involved in 3-hydroxylation of dihydrochalcones: polyphenol oxidases or the flavonoid 3′-hydroxylase (F3′H), which catalyzes B-ring hydroxylation of flavonoids. We isolated two F3′H cDNA clones from apple leaves and tested recombinant Malus F3′Hs for their substrate specificity. From the two isolated cDNA clones, only F3′HII encoded a functionally active enzyme. In the F3′HI sequence, we identified two putatively relevant amino acids that were exchanged in comparison to that of a previously published F3′HI. Site directed mutagenesis, which exchanged an isoleucine into methionine in position 211 restored the functional activity, which is probably because it is located in an area involved in interaction with the substrate. In contrast to high activity with various flavonoid substrates, the recombinant enzymes did not accept phloretin under assay conditions, making an involvement in the dihydrochalcone biosynthesis unlikely.

Polyphenol-Hydroxylating Tyrosinase Activity under Acidic pH Enables Efficient Synthesis of Plant Catechols and Gallols

Tyrosinase is generally known as a melanin-forming enzyme, facilitating monooxygenation of phenols, oxidation of catechols into quinones, and finally generating biological melanin. As a homologous form of tyrosinase in plants, plant polyphenol oxidases perform the same oxidation reactions specifically toward plant polyphenols. Recent studies reported synthetic strategies for large scale preparation of hydroxylated plant polyphenols, using bacterial tyrosinases rather than plant polyphenol oxidase or other monooxygenases, by leveraging its robust monophenolase activity and broad substrate specificity. Herein, we report a novel synthesis of functional plant polyphenols, especially quercetin and myricetin from kaempferol, using screened bacterial tyrosinases. The critical bottleneck of the biocatalysis was identified as instability of the catechol and gallol under neutral and basic conditions. To overcome such instability of the products, the tyrosinase reaction proceeded under acidic conditions. Under mild acidic conditions supplemented with reducing agents, a bacterial tyrosinase from Bacillus megaterium (BmTy) displayed efficient consecutive two-step monophenolase activities producing quercetin and myricetin from kaempferol. Furthermore, the broad substrate specificity of BmTy toward diverse polyphenols enabled us to achieve the first biosynthesis of tricetin and 3′-hydroxyeriodictyol from apigenin and naringenin, respectively. These results suggest that microbial tyrosinase is a useful biocatalyst to prepare plant polyphenolic catechols and gallols with high productivity, which were hardly achieved by using other monooxygenases such as cytochrome P450s.

Inactivation Kinetics and Thermodynamics Parameters of Polyphenol Oxidase and Peroxidase Activities in an Extract from of Violet Eggplant (Solanum melongena L.)

Enzymatic browning is associated with the action of polyphenol oxidases (PPO) and peroxidases (POD). The products of these enzymes cause undesirable changes of color and flavor of processed eggplant products. The present study aimed to evaluate kinetic properties and thermodynamics parameters of PPO and POD activities for controlling this undesirable process in extract from of violet eggplant. The effect of heat treatment on polyphenol oxidase and peroxidase activities in violet eggplant were studied over a range of 30 to 80 °C. T1/2-values of enzymatic activities are between 6.15 ± 0.03 and 13,27 ± 0,04 min at 80 °C, they decreased with increasing temperature, indicating a difference thermostability of each enzyme. D- and k-values decreased and increased, respectively, with increasing temperature, indicating faster of these enzymes inactivation at higher temperatures. Results suggested that polyphenol oxydase and peroxidase were relatively thermostable enzymes with a Z-value which from 50.25 and from 88.33 °C and Ea of 41.21 and of 27.78 kJmol-1. Thermodynamic parameters were also calculated. The Gibbs free energy ΔG values range from 43.24 ± 0,03 to 91.45 ± 0,01 kJ/mol. These kinetic data can be used to predict prevention of browning in the violet eggplant (Solanum melongena L.) by thermal inactivation of enzymes.