Characterization of a caffeic acid 3-O-methyltransferase from wheat and its function in lignin biosynthesis

Caffeic acid 3-O-methyltransferase (COMT) catalyzes the multi-step methylation reactions of hydroxylated monomeric lignin precursors, and is believed to occupy a pivotal position in the lignin biosynthetic pathway. A cDNA (TaCM) was identified from wheat and it was found to be expressed constitutively in stem, leaf and root tissues. The deduced amino acid sequence of TaCM showed a high degree of identity with COMT from other plants, particularly in SAM binding motif and the residues responsible for catalytic and substrate specificity. The predicted TaCM three-dimensional structure is very similar with a COMT from alfalfa (MsCOMT), and TaCM protein had high immunoreactive activity with MsCOMT antibody. Kinetic analysis indicated that the recombinant TaCM protein exhibited the highest catalyzing efficiency towards caffeoyl aldehyde and 5-hydroxyconiferaldehyde as substrates, suggesting a pathway leads to S lignin via aldehyde precursors. Authority of TaCM encoding a COMT was confirmed by the expression of antisense TaCM gene in transgenic tobacco which specifically down-regulated the COMT enzyme activity. Lignin analysis showed that the reduction in COMT activity resulted in a marginal decrease in lignin content but sharp reduction in the syringl lignin. Furthermore, the TaCM protein exhibited a strong activity towards ester precursors including caffeoyl-CoA and 5-hydroxyferuloyl-CoA. Our results demonstrate that TaCM is a typical COMT involved in lignin biosynthesis. It also supports the notion, in agreement with a structural analysis, that COMT has a broad substrate preference.     

Colonization and lignin decomposition of Camellia japonica leaf litter by endophytic fungi

Endophytic fungi occur on various types of leaf litter, but few studies have been done on their roles as saprophytes in decomposition. This study examined the succession of fungi in live, newly shed, and decomposing leaves at 2 months of decomposition of Camellia japonica and chemical changes in decomposing leaves colonized by endophytes. Coccomyces nipponicum, Lophodermium sp., Geniculosporium sp. 1, and Colletotrichum gloeosporioides were isolated from living leaves. Coccomyces nipponicum and Lophodermium sp. were also isolated frequently from newly shed and decomposing leaves. These two fungi caused a decrease of lignin content and bleaching in decomposing leaves under field and laboratory conditions. Total hyphal length in decomposing leaves was higher in bleached portions than in surrounding nonbleached portions, which probably reflected the early onset of hyphal growth of endophytes inside leaf tissue at leaf senescence or death. Incubation of newly shed leaves that were sterilized to exclude previously established endophytes resulted in no occurrence of bleached portions in decomposing leaves on the forest floor. This result indicated that these endophytes were incapable of colonizing leaves directly after litterfall and that the persistence of endophytes from live leaves was crucial for their colonization in decomposing leaves.     

Regional analysis of litter quality in the central grassland region of North America

Abstract. The central grassland region of North America is characterized by large gradients of temperature and precipitation. These climatic variables are important determinants of the distribution of plant species, and strongly influence plant morphology and tissue chemistry. We analysed regional patterns of plant litter quality as they vary with climate in grassland ecosystems throughout central North America including tall‐grass prairie, mixed grass prairie, shortgrass steppe, and hot desert grasslands. An extensive database from the International Biological Program and the Long‐Term Ecological Research Program allowed us to isolate the effects of climate from those of plant functional types on litter quality. Our analysis of grass species confirms a previously recognized positive correlation between C/N ratios and precipitation. Precipitation exhibited a similar positive relationship with lignin/N and percent lignin. Although there was no significant correlation between temperature and C/N, there was a significant positive relationship between temperature and both percent lignin and lignin/N. Among functional types, C₃ grasses had a slightly lower C/N ratio than C₄ grasses. Tall grass species exhibited higher C/N, lignin/N, and percent lignin than short grass species. This understanding of the regional patterns of litter quality and the factors controlling them provides us with a greater knowledge of the effect that global change and the accompanying feedbacks may have on ecosystem processes.     

Effects of growth differences due to geographic location and N-fertilisation on wood chemistry of Norway spruce

We studied the effect of long-term nitrogen fertilisation on wood chemistry at two boreal sites in Finland: the northern site (Kemijärvi) and the southern site (Heinola). N-fertilisation was repeated in five-year intervals from the 1960s. Norway spruce (Picea abies L. Karst.) trees that had been planted in 1938 and 1954, in the northern and the southern site, respectively, were harvested in October 2002. Altogether 20 trees, in five different size classes, either unfertilised or fertilised, were felled. Wood sections at breast height, consisting of five consecutive annual rings, from six (Kemijärvi) or five (Heinola) points with different distances from the pith were examined. Differences in growth between the northern and southern sites were marked in favour of the southern site. In the northern site fertilisation had clearly increased the diameter growth, while in the southern site fertilisation had no effect. Nitrogen fertilisation resulted in slight changes in wood chemistry that included increased nitrogen concentrations in the northern site and extractives in the southern site. Stem wood had higher concentrations of extractives, starch, and uronic acids, and lower concentration of cellulose, in the northern than in the southern site. Changes in the stem wood chemistry along radial axis were marked. The changes in wood chemistry are discussed in relation to the physiological function and also how the changes can influence the suitability of wood for different end-use purposes.     

Ligninolytic system of Phanerochaete chrysosporium: Inhibition by o-Phthalate

The degradation rate of [synthetic-¹⁴C]-lignin to ¹⁴CO₂ by Phanerochaete chrysosporium in cultures buffered with 0.01 M 2,2-dimethylsuccinate (DMS) was twice that in 0.01 M o-phthalate-buffered cultures. This difference could be totally accounted for by o-phthalate inhibition of the activity of the ligninolytic system. ¹⁴CO₂ production from ring-, sidechain-, and methoxyl-labeled lignins was inhibited, the degree of inhibition being dependent on o-phthalate concentration. Oxidations of ¹⁴C-glucose, ¹⁴C-acetovanillone, and ¹⁴C-apocynol were not inhibited; thus o-phthalate is not a general inhibitor, and might inhibit activities involved in attack of the lignin polymer. DMS is a suitable buffer for the ligninolytic system. Degradation rates of ring-labeled lignin to ¹⁴CO₂ of 10–15% in 24 h were obtained consistently over the pH range 3.6–4.5, with an optimum near pH 4.0.Non-Standard Abbreviations DMS dimethylsuccinate     

A map of rye chromosome 2R using isozyme and morphological markers

Summary The segregation of isozymic loci for leaf peroxidases (L2Per) has been investigated in backcrosses and F₂ offspring of rye lines having purple seeds (Ps) and monstrosum ears (mo). The Ps, L2Per-3b, mo, and L2Per-2 loci were linked. The Ps and mo loci have been previously located on the 2R chromosome, and the L2Per-3b and L2Per-2 loci have been located on the 2RS chromosome arm. The results favor the gene order Ps ... L2Per-3b ... mo ... L2Per-2 or Ps ... mo... L2Per-3b ... L2Per-2. The position of the loci relative to the centromere is still not known, but the obtained results suggest that the mo locus could be located on the 2RS chromosome arm. On the basis of previously reported linkage groups, the most probable arrangement of the loci located on chromosome 2R is: dw2 ... Ps ... (L2Per-3a ... L2Per-3b ... mo) ... L2Per-2. It has not been possible to know the position of L2Per-4 loci (also located on 2RS chromosome arm) relative to L2Per-3a and L2Per-3b loci.     

Quality of micropropagated plants—Vitrification

Summary Vitrification-Hyperhydrous shoot development, effects the survival and quality of several micropropagated plants ex-vitro. The leaves which are the immediate organ to be affected, exhibit abnormal morphology and physiology. Leaf malfunction is apparently a stress response to very rich media and high relative humidity. The understanding of the underlying mechanism of vitrification and its control in vitro can contribute to a more efficient micropropagation. Vitrification was found to be associated with elevated ethylene production which was related to hypolignification and poor cell wall development. Liquid and low agar media induced callose formation along with reduced and disoriented cellulose biosynthesis, manifested also in non-functioning guard cells. Malfunctioning stomata, in addition to defective cuticle contributed to increased transpiration and desiccation of in vitro formed leaves. The activity of various enzymes, associated with cell wall synthesis, was low and total proteins in normal leaves was higher than in vitreous ones. Various measures were found to reduce vitrification; lowered matrix and water potential in the medium, reduction in RH, low NH ₄ ⁺ , changes in Ca⁺⁺ levels and the removal of ethylene. These measures improved leaf morphogenesis, survival and the quality of several micropropagated plant species. Presented in the Session-in-Depth Transition of Plants From Culture to Establishment In Vivo,“ at the 41st Annual Meeting of the Tissue Culture Association, Houston, Texas, June 10–13, 1990.     

Potential Applications of the Oxidoreductive Enzymes in the Decolorization and Detoxification of Textile and Other Synthetic Dyes from Polluted Water: A Review

ABSTRACT

Recently, the enzymatic approach has attracted much interest in the decolorization/degradation of textile and other industrially important dyes from wastewater as an alternative strategy to conventional chemical, physical and biological treatments, which pose serious limitations. Enzymatic treatment is very useful due to the action of enzymes on pollutants even when they are present in very dilute solutions and recalcitrant to the action of various microbes participating in the degradation of dyes. The potential of the enzymes (peroxidases, manganese peroxidases, lignin peroxidases, laccases, microperoxidase-11, polyphenol oxidases, and azoreductases) has been exploited in the decolorization and degradation of dyes. Some of the recalcitrant dyes were not degraded/decolorized in the presence of such enzymes. The addition of certain redox mediators enhanced the range of substrates and efficiency of degradation of the recalcitrant compounds. Several redox mediators have been reported in the literature, but very few of them are frequently used (e.g., 1-hydroxybenzotriazole, veratryl alcohol, violuric acid, 2-methoxy-phenothiazone). Soluble enzymes cannot be exploited at the large scale due to limitations such as stability and reusability. Therefore, the use of immobilized enzymes has significant advantages over soluble enzymes. In the near future, technology based on the enzymatic treatment of dyes present in the industrial effluents/wastewater will play a vital role. Treatment of wastewater on a large scale will also be possible by using reactors containing immobilized enzymes.