Level Of Lignification Research Articles

The osmotic stress of Vallisneria natans (Lour.) Hara leaves originating from the disruption of calcium and potassium homeostasis caused by MC-LR

Aquatic plants are potentially impacted by microcystins (MCs) in lakes experiencing harmful algal blooms. However, how these plants respond, and possibly adapt to osmotic stress caused by MCs is unclear. Vallisneria natans is a pioneer taxon with a global distribution in eutrophic lakes. In this study, we investigated the effect of MC-LR on morphological structure, water retention, osmoregulatory ability, and homeostasis of calcium (Ca2+) and potassium (K+) ions in V. natans leaves. Results showed that the morphological changes caused by MC-LR included increased volumes of epidermal and mesophyll cells, changes in their lignification level, and the degradation of chloroplast structure and dissolution of starch granules. The increased moisture content and water potential with MC-LR concentration were consistent with the occurrence of osmotic stress, and the decreased osmotic potential implied the activation of osmoregulation. Soluble sugar and free amino acid concentrations increased at MC-LR treatments ≥10 μg/L, while inorganic ion K+ content increased in all MC-LR treatments. Although instantaneous K+inflow and Ca2+outflow occurred at 10 μg/L and 100 μg/L MC-LR, respectively, ≥1 μg/L MC-LR resulted in continuous K+ inflow and Ca2+ outflow within 24 h. Moreover, plasma membrane hyperpolarization was caused by MC-LR, especially at 1 and 10 μg/L. We suggest that Ca2+ efflux served as a signal molecule from the cytoplasmic matrix via Ca2+-ATPase, and the uptake of K+ was activated passively through transporters in response to MC-LR-induced plasma membrane hyperpolarization. Therefore, the uptake of K+ was a part of the response but not an adaptation to MC-LR stress, and is considered the cause for the uptake of water in leaves. Ca2+ and K+ homeostasis of V. natans leaves was disrupted by MC-LR concentrations as low as 1 μg/L, suggesting that aquatic plants in most eutrophic lakes may experience negative impacts such as Ca2+ loss, impacts to cell water balance, and alteration in cellular morphology, due to osmotic stress caused by MC-LR.

The PcMYB44-mediated miR397-PcLACs module regulates defence-induced lignification in pear resistance to fungal disease.

Diseases caused by Alternaria alternata and Botryosphaeria dothidea diminish pear yield and quality, and restrict the pear agricultural industry. Lignification is a conserved mechanism for plant resistance against pathogen invasion. The regulatory mechanisms underlying defence-induced lignification in pear in response to fungal pathogen infection remain unknown. In this study, analysis of lignification level and lignin content in pear revealed that A. alternata and B. dothidea induced lignification, and transcriptomics showed that lignin biosynthesis was affected. To explore whether laccases (LACs) mediated by miR397 regulate lignification in pear, we investigated the role of PcmiR397 in repressing the expression of PcLACs using 5'-RNA ligase-mediated-RACE and co-transformation in tobacco. Opposite expression patterns for PcmiR397 and PcLAC target genes were observed in pear in response to pathogens. Transient transformation in pear demonstrated that silencing PcmiR397 and overexpressing a single PcLAC enhanced resistance to pathogens via lignin synthesis. To further reveal the mechanism underpinning the PcMIR397 response of pear to pathogens, the PcMIR397 promoter was analysed, and pMIR397-1039 was found to be inhibited by pathogen infection. The transcription factor PcMYB44 was up-regulated, and it bound to the PcMIR397 promoter and inhibited transcription following pathogen infection. The results demonstrate the role of PcmiR397-PcLACs in broad-spectrum resistance to fungal disease, and the potential role of PcMYB44 involved in the miR397-PcLAC module in regulating defence-induced lignification. The findings provide valuable candidate gene resources and guidance for molecular breeding to improve resistance to fungal disease in pear.

Global transcriptome and targeted metabolite analyses of roots reveal different defence mechanisms against Ralstonia solanacearum infection in two resistant potato cultivars.

Ralstonia solanacearum (Rs), the causal agent of bacterial wilt disease in an unusually wide range of host plants, including potato (Solanum tuberosum), is one of the most destructive phytopathogens that seriously reduces crop yields worldwide. Identification of defence mechanisms underlying bacterial wilt resistance is a prerequisite for biotechnological approaches to resistance breeding. Resistance to Rs has been reported only in a few potato landraces and cultivars. Our in vitro inoculation bioassays confirmed that the cultivars 'Calalo Gaspar' (CG) and 'Cruza 148' (CR) are resistant to Rs infection. Comparative transcriptome analyses of CG and CR roots, as well as of the roots of an Rs-susceptible cultivar, 'Désirée' (DES), were carried out two days after Rs infection, in parallel with their respective noninfected controls. In CR and DES, the upregulation of chitin interactions and cell wall-related genes was detected. The phenylpropanoid biosynthesis and glutathione metabolism pathways were induced only in CR, as confirmed by high levels of lignification over the whole stele in CR roots six days after Rs infection. At the same time, Rs infection greatly increased the concentrations of chlorogenic acid and quercetin derivatives in CG roots as it was detected using ultra-performance liquid chromatography - tandem mass spectrometry. Characteristic increases in the expression of MAP kinase signalling pathway genes and in the concentrations of jasmonic, salicylic, abscisic and indoleacetic acid were measured in DES roots. These results indicate different Rs defence mechanisms in the two resistant potato cultivars and a different response to Rs infection in the susceptible cultivar.

Pb4CL2 Inducing Lignin Accumulation in Superficial Scald ‘Chili’ (Pyrus bretschneideri) Pear Fruit

Superficial scald of pear fruit is a physiological disorder that easily occurs during cold storage and seriously affects pear eating quality and commodity value. It is important to study the mechanism of superficial scald disorder. Our previous study reported that the incidence of superficial scald of calcium chloride (CaCl2)-treated pear fruit during storage was significantly lower than that of untreated fruit. In this study, we found that the accumulation of lignin in CaCl2-treated fruit was significantly lower than that of untreated fruit. The expression of the Pb4CL2 gene in the lignin synthesis pathway was downregulated in the CaCl2-treated fruit. The lignification level of the fruit overexpressing Pb4CL2 was significantly higher than that of the empty vector fruit. Therefore, we speculate that downregulation of Pb4CL2 after CaCl2 treatment plays an important role in CaCl2 inhibiting superficial scald disorder by affecting lignin accumulation in pear fruit.

Hydrogen-rich water alleviates chilling injury-induced lignification of kiwifruit by inhibiting peroxidase activity and improving antioxidant system.

Kiwifruit is prone to chilling stress and displays chilling injury (CI) such as lignification; however, the underlying physicochemical mechanism remains largely unknown. Here, the changes in levels of quality attributes, lignin biosynthesis, antioxidant system and sugars were compared in kiwifruit between control and hydrogen-rich water (HRW) treatments during cold storage for 90 days at 0°C. The results reveal that HRW is an effective measure for CI alleviation, as indicated by the decrease in lignification level with repressed peroxidase activity but enhanced polyphenol oxidase activity. The amelioration of membrane peroxidation was suggested by the repressed levels of H2 O2 and malondialdehyde. They were accompanied by the improvement of antioxidant system, which is supported by the enhancement of sugars including fructose and glucose. In conclusion, HRW can enhance chilling tolerance, as suggested by the alleviation of lignification through inhibiting peroxidase activity and elevating the antioxidant system to attenuate membrane peroxidation. © 2022 Society of Chemical Industry.

Genome-Wide Characterization of Laccase Gene Family from Turnip and Chinese Cabbage and the Role in Xylem Lignification in Hypocotyls

The turnip and the Chinese cabbage belong to the Brassica rapa subspecies, yet they have evolved marked differences in morphology. The turnip has a distinct swelled taproot, while the Chinese cabbage has a big leafy head. The turnip’s taproot is developed mainly by the hypocotyl. To explore the taproot formation, we firstly compared the vascular structure of the hypocotyl during the early developmental stages of the turnip and the Chinese cabbage, finding that there were observable differences in the number of xylem cells and the cell-wall lignification in the hypocotyl vascular tissues after the transition from primary to secondary growth. Laccases (LAC) play an important role in lignification by polymerizing monolignols in the cell wall, however, it is not clear whether differences in the lignification levels in the hypocotyl xylem cell walls are related to the genetic variations of the LAC gene family, between the turnip and the Chinese cabbage. Therefore, we systematically characterized the LAC genes from the turnip and the Chinese cabbage, and 27 LAC genes were identified in each. These LAC genes can be divided into six groups, and each LAC in the turnip is closely adjacent to that in the Chinese cabbage. Gene structure, conserved motif, and chromosomal localization were highly conserved between the turnip and the Chinese cabbage. We also compared the expression pattern of the laccases in the different tissues and hypocotyl’s early development stage, and the results clearly showed the different profiles between the turnip and the Chinese cabbage. Following a comprehensive analysis of these results, we predicted that LAC17.1 and LAC17.3 are two candidate genes that participate in the regulation of lignin synthesis during taproot formation. Our results provide a valuable clue for uncovering the regulation mechanism of the lower lignification level in the turnip’s hypocotyl and fundamental information for further studies of the LAC gene family in Brassica rapa.

ЛОКАЛИЗАЦИЯ АКВАПОРИНОВ В ПРОЦЕССЕ ФОРМИРОВАНИЯ ПОЯСКОВ КАСПАРИ В КОРНЯХ РАСТЕНИЙ ЯЧМЕНЯ

There are two main pathways for water transport in plants. One of them is water transport along the cell walls and xylem vessels, called apoplastic pathway, and the other is from cell to cell through the membrane water channels aquaporins. Formation of Casparian bands by suberin and lignin deposition reduces conductivity of the apoplastic pathway. So the role of membrane water transport should increase, as mentioned in many reviews. The aim of this research was to localize barley aquaporins of the HvPIP2 family in different root zones depending on the differentiation of cell walls and deposition of Casparian bands. It was shown that the intensity of berberine fluorescence was insignificant in the zone closer to the root tip (at a distance of 3–4 cm), however fluorescence increased in the endodermis and the central cylinder of the root basal zone, indicating high lignification of cell walls and deposition of lignin and suberin in developing Casparian bands. Localization of HvPIP2;1 and HvPIP2;5 aquaporins showed no differences in their level between different root zones. The use of antibodies against aquaporins HvPIP2;2 and HvPIP2;3/4 revealed a local increase in fluorescence in the endodermal region of the basal zone of the roots characterized by high level of lignification and suberinization which apparently should compensate for the expected decrease in hydraulic conductivity as a result of the formation of apoplastic barriers. It is possible that the role of different aquaporins in water transport varies depending on the growing conditions of plants.

Local Variations in Carbohydrates and Matrix Lignin in Mechanically Graded Bamboo Culms.

The mechanical performance of bamboo is highly dependent on its structural arrangement and the properties of biomacromolecules within the cell wall. The relationship between carbohydrates topochemistry and gradient micromechanics of multilayered fiber along the diametric direction was visualized by combined microscopic techniques. Along the radius of bamboo culms, the concentration of xylan within the fiber sheath increased, while that of cellulose and lignin decreased gradually. At cellular level, although the consecutive broad layer (Bl) of fiber revealed a relatively uniform cellulose orientation and concentration, the outer Bl with higher lignification level has higher elastic modulus (19.59–20.31 GPa) than that of the inner Bl close to the lumen area (17.07–19.99 GPa). Comparatively, the cell corner displayed the highest lignification level, while its hardness and modulus were lower than that of fiber Bl, indicating the cellulose skeleton is the prerequisite of cell wall mechanics. The obtained cytological information is helpful to understand the origin of the anisotropic mechanical properties of bamboo.

Seed coat lignification level is crucial in Capsicum spp seed longevity.

Capsicum (pepper) is known for its poor seed germination, particularly seed longevity is usually much shorter than other Solanaceae. However, the molecular mechanisms involved are mostly unknown in these species. The present study examines the differences in seed longevity among Capsicum species and varietal types. Feral or less domesticated species, such as Capsicum chinense and particularly Capsicum frutescens, showed higher germination rates than the more domesticated Capsicum annuum after accelerated seed aging treatments. In addition, variability was detected in the expression of genes involved in the response to seed deterioration. The differences observed in ASPG1 expression led us to study the seed protein profile in dry and germinating seeds. Seed storage protein mobilization during germination was faster in seed aging-resistant genotypes. Similarly, the transcriptional change observed for the orthologous gene of the trans-species regulator AtHB25 prompted us to study the structure and molecular components of the seed coat in peppers. All the Capsicum pepper accessions analyzed presented very lignified testa and we observed a positive correlation between the amount of lignin and seed viability. Our results provide essential information to explain the poor germination observed in pepper seeds and provide an experimental framework for future improvements in this important character.

Comparative transcriptomic analysis of genes involved in stem lignin biosynthesis in woody and herbaceous Paeonia species.

Paeonia is recognized globally due to its ornamental value. However, the mechanisms behind the formation of distinct levels of lignification in Paeonia stems remain largely unknown. In this study, we selected three representative Paeonia species, namely P. ostii (shrub), P. lactiflora (herb), and P. × 'Hexie' (semi-shrub), to evaluate and contrast their respective anatomical structure, phytochemical composition and transcriptomic profile. Our results showed that the degree of lignin deposition on the cell wall, along with the total amount of lignin and its monomers (especially G-lignin) were higher in P. ostii stems compared to the other two species at almost all development stages except 80 days after flowering. Furthermore, we estimated a total number of unigenes of 60,238 in P. ostii, 43,563 in P. × 'Hexie', and 40,212 in P. lactiflora from stem transcriptome. We then built a co-expression network of 25 transcription factors and 21 enzyme genes involved in lignin biosynthesis and identified nine key candidate genes. The expression patterns of these genes were positively correlated with the transcription levels of PAL, C4H, 4CL2, CCR, and COMT, as well as lignin content. Moreover, the highest relative expression levels of CCR, 4CL2, and C4H were found in P. ostii. This study provides an explanation for the observed differences in lignification between woody and herbaceous Paeonia stems, and constitutes a novel reference for molecular studies of stem-specific lignification process and lignin biosynthesis that can impact the ornamental industry.

CcBLH6, a bell-like homeodomain-containing transcription factor, regulates the fruit lignification pattern.

CcBLH6 is a bell-like homeodomain-containing transcription factor that plays an important role of lignin biosynthesis in the control of fruit lignification pattern in Camellia chekiangoleosa. The fruit of Camellia chekiangoleosa has a unique lignification pattern that features with a thick pericarp containing a low level of lignification. Yet the fruit lignification pattern and the regulatory network of responsible gene transcription are poorly understood. Here, we characterized a bell-like homeodomain-containing (BLH) transcription factor from C. chekiangoleosa, CcBLH6, in the control of fruit lignification. CcBLH6 expression was highly correlated with the unique lignification pattern during fruit development. The ectopic expression of CcBLH6 promoted the lignification process of stem and root in Arabidopsis. We found that expression of genes related to lignin biosynthesis and its transcriptional regulation was altered in transgenic lines. In a Camellia callus-transformation system, overexpression of CcBLH6 greatly enhanced the expression of genes related to lignin biosynthesis and its transcriptional regulation was altered in transgenic lines. In the callus-transformation system, overexpression of CcBLH6 greatly enhanced the lignification of parenchymal cells, and the regulation of several genes involved in lignin accumulation was largely consistent between Arabidopsis and Camellia. Our study reveals a positive role of CcBLH6 in the regulation of lignin biosynthesis during fruit lignification in Camellia.

Image analysis of stress-induced lignin deposition in Arabidopsis thaliana using the macro program LigninJ for ImageJ software.

In vascular plants, lignin is deposited during morphogenesis but also under stress conditions. Assessing the degree of stress-induced lignin deposition is complicated because it occurs locally and irregularly in plant tissues. In this study, we developed a macro program, LigninJ, for the open-source software ImageJ to automatically and efficiently determine areas and levels of lignification after Wiesner (phloroglucinol-HCl) staining. We used the CIELAB color space for detection of red color following the Wiesner reaction. In addition, LigninJ has a function for adjusting the background level and its white balance to reduce biases that are inherent to individual color images. Furthermore, LigninJ can be used for batch analyses of multiple images, taking about 2 s per image. In this study, we analyzed wound-induced lignin deposition in cotyledons of the Arabidopsis thaliana ecotypes Landsberg erecta and Columbia and assessed ectopic lignin depositions in roots of lignescence (lig) mutants of Arabidopsis. Our results confirmed that this method is efficient for evaluating the degree of stress-induced lignin deposition.

Responses of contrasting rice genotypes to excess manganese and their implications for lignin synthesis

Manganese (Mn) toxicity is frequently encountered in crops grown on soils with low pH or low redox potential, and harmful to plant development and growth. This study aimed at exploring adaptive mechanisms to Mn toxicity in rice, and investigated the effects of Mn toxicity on shoot lignification. Sixteen rice genotypes were grown in hydroponic solutions and exposed to normal (0.5 mg dm−3) or toxic (5 mg dm−3) Mn concentrations for three weeks. Morphological responses to Mn toxicity included a significant reduction in shoot length and the formation of visible symptoms scored as leaf damage index (LDI). Based on shoot Mn concentrations in the Mn toxic treatment, genotypes were classified as Mn includers and excluders. Across different genotypes, shoot Mn concentrations were significantly negatively correlated with relative shoot length and positively correlated with LDI. Consequently, the most tolerant genotypes in terms of morphology were all excluders, while the most sensitive genotypes were includers. The sensitive genotypes were also more responsive to manganese in terms of lipid peroxidation than tolerant genotypes. Shoots of rice plants grown in the high Mn treatment showed a higher level of lignification measured as thioglycolic acid lignin (TGAL), especially among Mn includers. TGAL was positively correlated with shoot Mn concentration and the levels of phenolics. In contrast, peroxidase activity was not responsive to the Mn treatment and was not significantly correlated with shoot lignification. In conclusion, exclusion is a dominant tolerance mechanism to Mn toxicity in rice. Further, Mn stimulated lignin biosynthesis in rice, especially in genotypes that were unable to exclude Mn.

Heterogenous expression of Pyrus pyrifolia PpCAD2 and PpEXP2 in tobacco impacts lignin accumulation in transgenic plants

Lignin, a natural macromolecular compound, plays an important role in the texture and taste of fruit. Hard end is a physiological disorder of pear fruit, in which the level of lignification in fruit tissues is dramatically elevated. Cinnamyl alcohol dehydrogenase and expansin genes (PpCAD2 and PpEXP2, respectively) exhibit higher levels of expression in ‘Whangkeumbae’ (Pyrus pyrifolia) pear fruit exhibiting this physiological disorder, relative to control fruit without symptoms. These genes were isolated from pear fruit and subsequently expressed in tobacco (Nicotiana tabacum) to investigate their function. Histochemical staining for lignin revealed that the degree of lignification in leaf veins and stem tissues increased in plants transformed with sense constructs and decreased in plants transformed with antisense constructs of PpCAD2. The expression of native NtCADs was also inhibited in the antisense PpCAD2 transgenic tobacco. Sense and antisense PpCAD2 transgenic tobacco exhibited an 86.7% increase and a 60% decrease in CAD activity, respectively, accompanied by a complementary response in lignin content in root tissues. The basal portion of the stem in PpEXP2 transgenic tobacco was bent and highly lignified. Additionally, the level of cellulose also increased in the stem of PpEXP2 transgenic tobacco. Collectively, these results suggested that PpCAD2 and PpEXP2 genes play a significant role in lignin accumulation in transgenic tobacco plants, and it is inferred that these two genes may also participate in the increased lignification observed in hard end pear fruit.

Genetic and Quantitative Trait Locus Analysis of Cell Wall Components and Forage Digestibility in the Zheng58 × HD568 Maize RIL Population at Anthesis Stage.

The plant cell wall plays vital roles in various aspects of the plant life cycle. It provides a basic structure for cells and gives mechanical rigidity to the whole plant. Some complex cell wall components are involved in signal transduction during pathogenic infection and pest infestations. Moreover, the lignification level of cell walls strongly influences the digestibility of forage plants. To determine the genetic bases of cell wall components and digestibility, quantitative trait locus (QTL) analyses for six related traits were performed using a recombinant inbred line (RIL) population from a cross between Zheng58 and HD568. Eight QTL for in vitro neutral detergent fiber (NDF) digestibility were observed, out of which only two increasing alleles came from HD568. Three QTL out of ten with alleles increasing in vitro dry matter digestibility also originated from HD568. Five–ten QTL were detected for lignin, cellulose content, acid detergent fiber, and NDF content. Among these results, 29.8% (14/47) of QTL explained >10% of the phenotypic variation in the RIL population, whereas 70.2% (33/47) explained ≤10%. These results revealed that in maize stalks, a few large-effect QTL and a number of minor-effect QTL contributed to most of the genetic components involved in cell wall biosynthesis and digestibility.

Anatomical features of an African sorghum landrace adapted to flooded conditions

This research aims to evaluate adaptation of two contrasting sorghum genotypes to flooding: a landrace from Cameroon described as a “floating sorghum” (Wulaga) and a typical dryland improved variety (Cirad437) from Burkina Faso. Anatomical and morphological features of the basal internodes were quantified in control conditions (drained pots) and long-term flooded conditions from the five-leaf stage for the entire cropping cycle. This study revealed that the Wulaga variety expressed aerenchyma in basal internodes in both control and flooded treatments (constitutive aerenchyma) whereas Cirad437 only developed aerenchyma in flooded conditions (inducible aerenchyma). The level of lignification and epidermis thickness of basal internodes was identical for the two varieties and the two treatments, suggesting that lignin does not contribute to the enhancement of a tight barrier against O2 losses. However, Cirad437 showed shorter and larger internodes in flooded conditions while Wulaga did not show any difference between the two conditions. Results indicate the existence of diversity in adaptive response to flooded conditions for the two varieties. Further studies on phenotypic traits associated with phenology, leaf traits, root traits and yield components, are needed to confirm these preliminary results and to explore a broader range of genetic diversity that could be used for future sorghum breeding programs designed for flood-prone environments. (Resume d'auteur)

Plant cell wall and mechanisms of resistance to pathogens

A huge variety of phytopathogens (viruses, bacteria, and fungi) are potentially able to infect plant tissues and cause diseases. Numerous plant genes control a complex network of defense mechanisms based on both constitutive and inducible processes. The cell wall is a primary barrier the pathogens have to penetrate to start the infection process. Resistance at the level of the cell wall can prevent invasion of most potential pathogens. The cell wall structure may differ in various plant species. It is based on the network of cellulose microfibrils linked by hemicellulose molecules. In the growing parts of the plant, this network is integrated into the matrix of pectin polysaccharides. In the formed tissues, the cell wall is reinforced with lignin. In addition to polysaccharides, the cell wall contains a significant number of proteins implementing structural and enzymatic functions. The WallProtDB database stores information on many proteins of the cell wall of different plant species. Each of the cell wall components contributes to the formation of resistance to pathogens. The sites of contact with potential pathogens are characterized by the additional strengthening of the cell wall and the accumulation of antimicrobial secondary metabolites. The pathogens secrete enzymes that can break down the components of the cell wall. In response to the attack of microbes the plant produces inhibitors of microbial hydrolytic enzymes. The plant is also able to assess the number of components of the cell wall. For instance, mutants deficient for cellulose normally have an increased level of lignification and an increased defense response. Emerging after the action of microbial enzymes, low-molecular-weight cell wall fragments perform the signal function, enhancing the protective response of the plant. Thus, the cell wall is a dynamic structure, which can prevent the invasion of the majority of potential pathogens and initiate different variants of the immune response. Reconstruction of gene networks that control the structural and functional organization of the cell wall during the growth and under biotic and abiotic stress is crucial for understanding the molecular mechanisms of development and stress resistance. The review deals with the mechanisms of specific and nonspecific resistance of plants to pathogens of different nature, which are related to the cell wall. The cell wall structure and the role of various components in the detecting the invasion of plant pathogens and the induction of defense mechanisms are discussed.

The effect of colloidal silver nanoparticles on the level of lignification and hyperhydricity syndrome in Thymus daenensis vitro shoots: a possible involvement of bonded polyamines

Hyperhydricity syndrome (HHS) occurs when plants are stressed resulting in sharp changes in the ethylene concentration in the in vitro culture. One of the characteristics of HHS is the reduction of cell wall lignification. The aim of this study was to examine the effects of silver nanoparticles (AgNPs) on HHS in micropropagated Thymus daenensis shoots. AgNPs (0, 1, 2.5, or 5 mg L−1) were mixed with Murashige and Skoog (MS) culture medium and the antioxidant response and variations in lignin content were measured on micropropagated shoots derived from seedlings cultured with AgNPs. In addition, the different forms of microshoot polyamines (PAs) were investigated through High Performance Thin Layer Chromatography (HPTLC). The results indicated that seedling pretreatment with AgNPs at concentrations of 1 and 2.5 mg L−1 led to a decrease in the activity of the microshoot antioxidant system resulting in an increase of H2O2. Furthermore, the increased lignin content in response to the 2.5 mg L−1AgNPs treatment was accompanied by an increase in the concentration of the bonded form of putrescine (Put) and spermine (Spm). There was a direct correlation between the lignin content and the concentration of bonded PAs. We hypothesize that the higher level of bonded PAs reduced the concentration of the free forms, leading to increased lignification. This may have led to the decreased HHS observed in shoot cultures.

Extent of availability of major nutrients from selected Cereal Crop Residues to dairy ruminants as an alternative Dry Season Forage in Northern Uganda.

This work aimed at determining the availability of major nutrients from cereal crop residues (CRs) of maize, rice and sorghum to dairy ruminants in Northern Uganda. The major nutrient composition of the CRs was determined to establish their potential as alternative dry season forage resources for dairy animals. The CRs were selected based on crop economic importance and availability at the on-set of the dry season in randomly selected sub-counties of Lira, Otuke and Kole districts. Five samples of each CR were obtained from 20 farmer’s fields immediately after harvesting of each crop. Chemical analyses measured included Dry matter (DM), Crude protein (CP), Acid detergent fiber (ADF), Neutral detergent fiber (NDF), Digestible energy (DE), Organic matter digestibility (OM dig), Calcium (Ca), and Phosphorous (P). Fresh maize stover (MSF) had the highest CP (70.5g/kg DM), DE (11.3 MJ/kg DM), and lowest lignifications (49g/kg DM). Rice straw (RS) had a CP (42.1g/kg DM), lowest DE (6.9MJ/kg DM) and OM dig (506 g/kg DM). Dry maize stover (MSD) had the highest lignifications (76.0 g/kg DM) and low OM dig (543 g/kg DM) and sorghum stover (SS) had the lowest CP (40.0 g/kg DM) and a very low DE (7.1MJ/kg DM). The low CP levels and high levels of lignification limit the digestibility of the CR. However, their CF digestibility can be improved using an energy rich by-product, molasses (12.7MJ/kg DM) while the CP limitation due to ligfications can be improved through urea treatment.

Distribution of lignin and cellulose in compression wood tracheids of Pinus yunnanensis determined by fluorescence microscopy and confocal Raman microscopy

A detailed understanding of the topochemistry of compression wood tracheid walls is important from the perspectives of plant biochemistry and commercial utilization. The present study aimed to determine the anatomy and distribution of lignin and cellulose in situ in compression wood tracheids of Pinus yunnanensis by fluorescence microscopy and confocal Raman microscopy. Anatomical observation by fluorescence microscopy revealed that P. yunnanensis can be classified as mild compression wood and the lignin distribution in tracheid walls was heterogeneous. Confocal Raman microscopy was used to examine the distribution of lignin and cellulose within morphologically distinct tracheid wall regions. The histochemical observations indicated that the highest level of lignification occured in the cell corners middle lamella (CCML) some what less in the outer S2 layer (S2L), while the lowest lignin concentration was found in the S2. In contrast, cellulose distribution showed the opposite pattern with the highest cellulose concentration occurring in the S2 layer. The Raman analysis also indicated that the cellulose microfibril angle (MFA) in the S1 was high and thus the cellulose fibrils and the CC, CO stretching occur at a large angle.