Screening of Pleurotus ostreatus isolates for their ligninolytic properties during cultivation on natural substrates

Thirteen basidiospore-derived isolates of Pleurotus ostreatus f6 strain differing in the level of ligninolytic enzyme production and other characteristics (mycelium extension rate, colony morphology) from the parental strain were cultivated on natural substrates. Under these conditions ligninolytic enzyme activity, loss of organic mass, polycyclic aromatic hydrocarbons (PAHs) degradation and colonization of sterile and nonsterile soil were studied. The activity of ligninolytic enzymes was substantially higher in straw than in liquid culture, although the differences between the isolates were less pronounced on this substrate. Some of the isolates showed a very good ability to decompose the lignocellulosic substrate (straw) and a relatively high loss of organic mass was found after 50 days of cultivation in these strains. The original strain f6 and isolates B13 and B26 successfully degraded all seven tested PAH compounds present in experimental soil samples, but the higher or lower ligninolytic enzyme production of isolates tested had no substantial effect on the extent of the degradation. In our screening, six basidiospore-derivedisolates growing well in nonsterile soil were found, whichcould be suitable for the prospective biotechnological exploitation.     

Role of peroxidases and glycosidases in regulation of sink size in developing seeds of Hibiscus esculentum

Changes in peroxidases and glycosidases activities in cytoplasmic and ionically wall-bound fraction of developing seed of Hibiscus esculentum were studied. In both fractions, the activity of peroxiases assayed with ferulic acid and caffeic acid as a hydrogen donors, showed inverse correlation with the cell enlargement (sink size development phase). Activities of glycosidases, on the other hand, showed positive correlation with the sink development and sink filling period of the developing seed. The role of both the enzymes, glycosidases and peoxidase in seed development is discussed.     

Effect of some plant growth regulator treatments on apple fruit ripening

The activity of IAA oxidase (IAAox), peroxidases (POD), and polyphenoloxidases (PPO), as affected by different pre-harvest growth regulator treatments (ABA, AVG, NAA, PDJ), was determined in on-tree ripening apples (cv. Golden Delicious) before and during the ethylene climacteric. The production of ethylene was inhibited by AVG and delayed by NAA, whereas ABA and PDJ treatments caused, in the on-tree remaining fruits, a marked fruit drop and a decrease or a slight increase in ethylene levels respectively. While all treatments reduced POD activity, jasmonate increased IAAox and PPO activity. The inhibitory effect of NAA on all enzyme activity seems related to interference with C₂H₂ action or to a reduced sensitivity of the fruit abscission zone tissues to the hormone. The observed high fruit drop induced by ABA treatment made it impossible to detect differences in enzyme activity. AVG-treated fruits showed no substantial effects on IAAox and PPO activity in comparison to the control, a finding that seems to be related to a delay in all senescence processes caused by the very low level of the inhibited ethylene production. In control fruits IAAox activity increased during the initial ripening stages and decreased thereafter, POD activity increased throughout ripening and PPO showed little variation.     

Structural motifs of syringyl peroxidases predate not only the gymnosperm-angiosperm divergence but also the radiation of tracheophytes

* The most distinctive variation in the monomer composition of lignins in vascular land plants is that found between the two main groups of seed plants. Thus, while gymnosperm lignins are typically composed of guaiacyl (G) units, angiosperm lignins are largely composed of similar levels of G and syringyl (S) units. * However, and contrary to what might be expected, peroxidases isolated from basal (Cycadales and Ginkgoales) and differentially evolved (Coniferales and Gnetales) gymnosperms are also able to oxidize S moieties, and this ability is independent of the presence or absence of S-type units in their lignins. * The results obtained led us to look at the protein database to search for homologies between gymnosperm peroxidases and true eudicot S-peroxidases, such as the Zinnia elegans peroxidase. * The findings showed that certain structural motifs characteristic of eudicot S-peroxidases (certain amino acid sequences and beta-sheet secondary structures) predate the gymnosperm-angiosperm divergence and the radiation of tracheophytes, since they are found not only in peroxidases from basal gymnosperms, ferns and lycopods, but also in peroxidases from the moss Physcomitrella patens (Bryopsida) and the liverwort Marchantia polymorpha (Marchantiopsida), which, as typical of bryophytes, do not have xylem tissue nor lignins.     

Inducible and constitutive mechanisms of salt stress resistance in <Emphasis Type="Italic">Geum urbanum</Emphasis> L.

The avens (Geum urbanum L.) seedlings were grown for 6 weeks until the expansion of five to six leaves and then exposed to salinity shock (300 mM NaCl in the nutrient medium) or to a gradual (within 4 days) increase in NaCl concentration from 100 to 400 mM. The dynamics of stress-dependent accumulation of Na⁺, Cl^?, proline, and polyamines in leaves and roots was measured, together with activities of antioxidant enzymes, namely, superoxide dismutase (SOD) and guaiacol-dependent peroxidase occurring in soluble, ionically bound, and covalently bound forms. It is shown that avens plants can adapt to gradual salinization by mobilizing stressinducible protective mechanisms (accumulation of proline and spermine) and by activating constitutive enzyme systems (SOD and peroxidase).     

The cell biology of lignification in higher plants

Background Lignin is a polyphenolic polymer that strengthens and waterproofs the cell wall of specialized plant cell types. Lignification is part of the normal differentiation programme and functioning of specific cell types, but can also be triggered as a response to various biotic and abiotic stresses in cells that would not otherwise be lignifying.Scope Cell wall lignification exhibits specific characteristics depending on the cell type being considered. These characteristics include the timing of lignification during cell differentiation, the palette of associated enzymes and substrates, the sub-cellular deposition sites, the monomeric composition and the cellular autonomy for lignin monomer production. This review provides an overview of the current understanding of lignin biosynthesis and polymerization at the cell biology level.Conclusions The lignification process ranges from full autonomy to complete co-operation depending on the cell type. The different roles of lignin for the function of each specific plant cell type are clearly illustrated by the multiple phenotypic defects exhibited by knock-out mutants in lignin synthesis, which may explain why no general mechanism for lignification has yet been defined. The range of phenotypic effects observed include altered xylem sap transport, loss of mechanical support, reduced seed protection and dispersion, and/or increased pest and disease susceptibility.     

Rice 14-3-3 protein (GF14e) negatively affects cell death and disease resistance

Plant 14-3-3 proteins regulate important cellular processes, including plant immune responses, through protein-protein interactions with a wide range of target proteins. In rice (Oryza sativa), the GF14e gene, which encodes a 14-3-3 protein, is induced during effector-triggered immunity (ETI) associated with pathogens such as Xanthomonas oryzae pv. oryzae (Xoo). To determine whether the GF14e gene plays a direct role in resistance to disease in rice, we suppressed its expression by RNAi silencing. GF14e suppression was correlated with the appearance of a lesion-mimic (LM) phenotype in the transgenic plants at 3 weeks after sowing. This indicates inappropriate regulation of cell death, a phenotype that is frequently associated with enhanced resistance to pathogens. GF14e-silenced rice plants showed high levels of resistance to a virulent strain of Xoo compared with plants that were not silenced. Enhanced resistance was correlated with GF14e silencing prior to and after development of the LM phenotype, higher basal expression of a defense response peroxidase gene (POX22.3), and accumulation of reactive oxygen species (ROS). In addition, GF14e-silenced plants also exhibit enhanced resistance to the necrotrophic fungal pathogen Rhizoctonia solani. Together, our findings suggest that GF14e negatively affects the induction of plant defense response genes, cell death and broad-spectrum resistance in rice.     

Phenoloxidase-like activities and the function of virus-like particles in ovaries of the parthenogenetic parasitoid Venturia canescens

The ichneumonid endoparasitoid Venturia canescens successfully develops inside the hemocoel of another insect by using maternal protein secretions, including nucleic acid-free virus-like particles (VLPs), to manipulate host physiology. These VLPs consist of four major proteins, which are produced mainly in the calyx tissue and transferred into the host insect together with the egg. One of the protein-coding genes (vlp1), with similarities to phospholipid-hydroperoxide glutathione peroxidases (PHGPx), exists in allelic forms producing two protein variants with different protein properties. Here, we summarise observations indicating that oocytes and eggs are the source of reactive electrons, which potentially damage the lining and membranes of calyx tissues. We discuss the possible role of VLP1 in counteracting the damaging effects of oxidised phospholipids on membranes surrounding VLPs in the calyx lumen.