The molecular mechanisms underlying cell wall digestibility in maize (Zea mays L.) have been studied in three sets of maize brown-midrib isogenic lines in the genetic background of inbreds 1332 (1332 ...and 1332 bm3), 5361 (5361 and 5361 bm3), and F2 (F2, F2 bm1, F2 bm2, and F2 bm3). Two complementary approaches, SSH (suppression subtractive hybridization) and microarray-based expression profiling, were used to isolate and identify candidate genes in isogenic lines for bm mutants. Metabolic pathway analysis revealed that transcriptional events caused by altering the expression of a single bm gene involve all metabolic and signaling pathways. 53 ESTs were differentially expressed in all three isogenic bm3 comparisons, whereas 32 ESTs were consistently differentially expressed in different bm isogenic lines in F2 background. About 70% ESTs isolated by SSH were not present on the unigene microarray, demonstrating the usefulness of the SSH procedure to identify genes related to cell wall digestibility. Together with lignin analysis by cellular UV-microspectrophotometry, expression profiling in isogenic bm lines proved to be useful to understand alterations at the sub-cellular and molecular level with respect to lignin composition. The down-regulation of COMT affected the expression of CCoAOMT genes and caused a reduced content both of G and S units in bm3 mutants.
Tension wood of Laetia procera (Poepp.) Eichl. (Flacourtiaceae), a neo-tropical forest species, shows a peculiar secondary wall structure, with an alternance of thick and thin layers, while opposite ...wood of this species has a typical secondary wall structure (S1 + S2 + S3). Samples for the study of microstructural properties were collected upon the estimation of growth stresses in the living tree, in order to analyze the correlation of the former with the latter. Investigation using optical microscopy, scanning electron microscopy and UV microspectrophotometry allowed the description of the anatomy, ultra-structure and chemistry of this peculiar polylaminate secondary wall. In the thick layers, cellulose microfibril angle is very low (i.e., microfibril orientation is close to fibre axis) and cellulose microfibrils are well organized and parallel to each other. In the thin layers, microfibrils (only observable in the inner layer) are less organized and are oriented with a large angle relative to the axis of the cell. Thick layers are lightly lignified although thin layers show a higher content of lignin, close to that of opposite wood secondary wall. The more the wood was under tensile stress, the less the secondary wall was lignified, and lower the syringyl on guaiacyl lignin units' ratio was. The innermost layer of the secondary wall looks like a typical S3 layer with large microfibril angle and lignin occurrence. The interest of this kind of structure for the understanding of stress generation is discussed.
• Background and Aims Information on the influence of wounding on lignin synthesis and distribution in differentiating xylem tissue is still scarce. The present paper provides information on cell ...modifications with regard to wall ultrastructure and lignin distribution on cellular and subcellular levels in poplar after wounding. • Methods Xylem of Populus spp. close to a wound was collected and processed for light microscopy, transmission electron microscopy and cellular UV microspectrophotometry. Cell wall modification with respect to lignin distribution was examined at different stages of wound tissue development. Scanning UV microspectrophotometry and point measurements were used to determine the lignin distribution. • Key Results Xylem fibres within a transition zone between differentiated xylem laid down prior to wounding and the tissues formed after wounding developed distinctively thickened secondary cell walls. Those modified walls and cell corners showed, on average, a higher lignin content and an inhomogeneous lignin distribution within the individual wall layers. • Conclusions The work presented shows that wounding of the xylem may induce a modified wall architecture and lignin distribution in tissues differentiating at the time of wounding. An increasing lignin content and distinctively thickened walls can contribute to improved resistance as part of the compartmentalization process.
Summary
The localisation of lignin and phenolic extractives in woody tissue was determined using scanning UV
microspectrophotometry. This improved cellular analytical technique enabled direct imaging ...of the topochemical
lignin distribution within individual cell wall layers with a resolution of 0.25 μm
2
. Selected
softwood (
Picea abies
), hardwood (
Fagus sylvatica
,
Entandrophragma cylindricum, Prunus serotina
)
and monocotyledon (
Phyllostachys edulis
) sections of 1 μm thickness were scanned at a fixed wavelength
and evaluated with the “APAMOS” software. This approach allowed the distribution pattern of
lignins and aromatic extractives within the cell wall to be visualised simultaneously. The method was
found to be ideally suited to the study of their subcellular distribution in plant cell walls.
The topochemical distribution of phenolic deposits in the vessels of afzelia (Afzelia spp.) and merbau (Intsia spp.) heartwood was investigated by means of cellular UV microspectrophotometry (UMSP) ...to characterise the chemical composition and synthesis by pit membrane-associated enzymes. UV absorbance spectra of the deposits attached to the vessel walls of merbau are characterised by a distinct maximum at a wavelength of 368 nm representing the UV absorbance of pure robinetin (C15H10O7). Deposits in the vessels of afzelia display a typical spectrum of kaempferol (C15H10O2) with two distinct maxima at 270 and 350 nm. The pit membranes and pit canals of associated vessel and parenchyma cells are impregnated by these compounds. These results verify the assumption that the synthesis of deposits in afzelia and merbau is regulated by pit membrane-associated enzymes.
This research is a multifaceted study which investigates not only the role of melanin in providing photostability to natural hair color and hair proteins, but also the claim that the presence of ...specific artificial colors in hair slows down the rate of photodegradation of hair proteins. In earlier studies, the extractability of protein from photodegraded hair was investigated and showed that many of the cleaved proteins could not be extracted because of photo‐oxidative cross‐linking. The current study investigates the effect of the amount of melanin in hair of different ethnicity and the presence of artificial hair colors on the extractability of the main classes of hair proteins. Furthermore, the data are used in the interpretation of the effect of these components in being able to prevent photo‐oxidative damage to hair proteins.
When exposed to sunlight, hair undergoes changes in chemical, mechanical and morphological properties. The UVB and UVA regions of the solar spectrum are the most damaging to human hair. Of these two, the UVA region is predominant in the solar spectrum at low altitudes. Hair of different ethnicity responds differently to the damaging radiation of the solar spectrum, because of different amounts of melanin present in hair. Melanin absorbs the impinging radiation (especially at the lower wavelengths (254–350 nm), and converts it by some complex internal mechanism into heat. Because of this, melanin provides a photochemical protection to natural hair color and hair proteins and prevents their photodegradation. However, the melanin pigments act sacrificially and become themselves degraded in the process of protecting the proteins from light. As a result, this «protective» effect of the melanin pigments does not last during long‐term intense exposure, when, regardless of the amount of melanin in hair, most matrix, intermediate filament and high molecular weight hair proteins undergo photo‐oxidative cross‐linking into higher molecular weight species, and their extractability from hair decreases significantly.
The goal of this study is to demonstrate how UV‐radiation affects natural and artificial hair color during long‐term exposures. Bright‐field and UV‐microspectrophotometry and an electrophoretic separation technique (SDS‐PAGE) were chosen as investigative techniques for these studies, because they are well‐suited to accurately and reproducibly investigate the initial properties of a specific hair sample and the changes in these properties as a result of long‐term light‐exposure. The goal of this paper is not to relate this to the content and type of melanin in hair. Electrophoresis, while not measuring the exact quantitative amount of protein extracted, is a semi‐quantitative method, where increases in brightness of the bands represent increased amounts of proteins that were extracted of that specific protein from hair. This electrophoretic study attempts to determine whether the presence of natural or artificial color in hair influences the protein extractability in unaltered hair and the photo‐oxidative cross‐linking during light‐exposure.
The bright‐field microspectrophotometric study showed that high concentrations of melanin provide protection to the melanin itself and that they prevent loss of natural hair color during light‐exposure. However, neither large amounts of melanin in hair of different ethnicity, nor artificial hair colors (even a dye with an absorption in the UV region) provide protection to the hair proteins against photodegradation under the conditions used in this study.
UV‐microspectrophotometry has suggested the formation of high levels of photo‐oxidized proteins as a result of light‐exposure. Electrophoresis revealed photo‐oxidative cross‐linking of most matrix, intermediate filament and high molecular weight hair proteins into their higher molecular weight analogues, rendering them less extractable due to their lowered diffusivity. Only very low levels of low molecular weight matrix proteins could be extracted.
Intervessel pits play a key role in trees' water transport, lying at the base of drought-induced embolism, and in the regulation of hydraulic conductivity via hydrogels bordering pit canals. ...Recently, their microstructure has been the focus of numerous studies, but the considerable variation, even within species and the histochemistry of pit membranes, remains largely unexplained. In the present study, intervessel pits of the outermost wood were examined for Avicennia marina, of dry and rainy season wood separately for Rhizophora mucronata. The thickness of the pit membranes was measured on transmission electron micrographs while their topochemical nature was also analyzed via cellular UV microspectrophotometry. Pit membranes of R. mucronata were slightly thicker in dry season wood than in rainy season wood, but their spectra showed for both seasons a lignin and a yet unidentified higher wavelength absorbing component. It was suggested to be a derivative of the deposits, regularly filling pit canals. The vestures of A. marina chemically resembled pit membranes rather than cell walls.
Enzymatic and topochemical aspects of lignification were studied in a Pinus radiata D. Don cell culture system that was induced to differentiate tracheary elements and sclereids with lignified ...secondary cell walls. The activities of the lignin-related enzymes phenylalanine ammonia lyase (PAL; EC 4.3.1.5) and cinnamyl alcohol dehydrogenase (CAD; EC 1.1.1.195) increased concomitantly with cell differentiation, indicating that the increase in enzyme activity was related to lignification of the cell walls and was not induced by stress. This result also indicates that PAL and CAD are suitable markers for tracheary element differentiation in coniferous gymnosperms. To further characterize lignification in this cell culture system, cellular UV-microspectrophotometry and thioacidolysis were employed. Typical UV-absorption spectra of lignin were obtained from the secondary cell walls of the tracheary elements and sclereids and from the compound middle lamella connecting differentiated cells, and the presence of lignin was confirmed by thioacidolysis. Certain aspects of lignin topochemistry in the cell walls of the tracheary elements were similar to cell walls of P. radiata wood, such as the high lignin concentration in the compound middle lamella connecting adjacent cells and the lower lignin concentration in the secondary cell walls. Therefore, the P. radiata cell culture system appears to be well suited to study the formation of lignified secondary cell walls in coniferous gymnosperms.
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