Effects of UV-B treatment on controlling lignification and quality of bamboo (Phyllostachys prominens) shoots without sheaths during cold storage

For evaluating the effects of UV-B treatment on lignification and quality of bamboo(Phyllostachys prominens) shoots during postharvest, fresh bamboo shoots without sheaths were irradiated with UV-B at a dose of 8.0 kJ m^(–2) and then stored at(6±1)℃ along with 85–90% relative humidity(RH) for 15 d. The results showed that UV-B treatment apparently slowed down the increase rates of flesh firmness, weight loss, and contents of cellulose and lignin. It also decreased the activities of 4-coumarate CoA ligase(4CL), peroxidase(POD), cinnamyl alcohol dehydrogenase(CAD) and phenylalanine ammonialyase(PAL) and the expression of their encoding genes during cold storage. It was suggested that these effects of UV-B treatment on decreases in these enzymatic activities and the expression of encoding genes might collectively regulate lignin synthesis and accumulation in the flesh of bamboo shoots and consequently benefit in maintaining the edible quality of bamboo shoots during cold storage.

Polypropylene crisper and 1-MCP delay the softening,lignification and transcription levels of related enzyme genes of golden needle mushrooms(Flammulina velutipes)

The fresh postharvest golden needle mushroom(Flammulina velutipes) sporocarp has a high moisture content and crisp texture, but it still has high physiological activity and respiration, leading to senescence and quality deterioration.Treatments with 1-methylcyclopropene(1-MCP) and polypropylene(PP) crispers were used to study the changes of lignification and softening of F. velutipes during storage. The main findings were as follows: the crisper packaging could effectively prolong the storage time of F. velutipes;either the 1-MCP treatment, crisper packaging or the combination of the two treatments could significantly inhibit the accumulation of lignin and the decreases in the contents of cellulose and pectin, and had certain inhibitory effects on the activities of enzymes involved in lignification and softening including phenylalanine ammonia-lyase(PAL), cinnamyl alcohol dehydrogenase(CAD), cellulase(Cx), pectin methylesterase(PME) and polygalacturonase(PG). Among them, the inhibitory effect of the crisper packaging was higher than the 1-MCP treatment, while the combination of the two treatments was the best. The results of transmission electron microscopy(TEM) and scanning electron microscopy(SEM) showed that the crisper packaging in combination with the 1-MCP treatment could effectively maintain the integrity and stability of the F. velutipes cellular structure and inhibit the emergence of plasmolysis to prevent cell membrane rupture. The transcription levels showed that the crisper packaging and the combination of the 1-MCP treatment and crisper packing could effectively affect the expression of genes for enzymes related to lignification and softening of F. velutipes. In conclusion, 1-MCP and PP crispers could delay the lignification and softening of F. velutipes during storage.

Common Mechanism of Lignification of Compression Wood in Conifers and Buxus

Woody plants develop a specialized secondary xylem known as reaction wood to enable formation of an ideal shape. Reaction wood in coniferous species is known as compression wood, and that of woody angiosperms as tension wood. However, the genus Buxus which is classified as an angiosperm, forms compression-wood-like reaction wood. We investigated the mechanism of lignification in coniferous compression wood and Buxus reaction wood: 1) Several lignin synthesis genes were upregulated in differentiating reaction wood of Buxus microphylla;2) B. microphylla possesses a specific laccase gene that is expressed specifically in differentiating reaction wood (BmLac4);3) laccase activity localization was closely related to lignification of reaction wood, and laccase activity was high in the secondary wall middle layer;4) in reaction wood cell walls, galactan was present in the outer portion of the secondary wall middle layer, and the level of xylan was reduced. These findings suggest that lignification in B. microphylla reaction wood is identical to that of coniferous compression wood. These may represent general mechanisms of increasing lignin content in various reaction woods.

The Effect of Lignification Process on the Bioconversion Efficiency in Moso Bamboo

Recalcitrance of lignocellulosic biomass is closely related to the presence of lignin in secondary cell walls,which has a negative effect on enzyme digestibility,biomass-to-biofuels conversion,and chemical pulping.The lignification process and structural heterogeneity of the cell wall for various parts of moso bamboo were investigated.There were slight differences among three different column parts of moso bamboo in terms of chemical compositions,including cellulose,hemicelluloses,and lignin.However,the detailed analysis of the fractionated lignin indicated that the acid-soluble lignin was first biosynthesized,and the largest molecular weight value was detected from the bottom part of the moso bamboo,as well as the highest syringyl-to-guaiacyl ratio.Although the main b-O-4 aryl ethers and resinol structures were clearly present in all lignin samples examined by NMR analysis,the relatively small lignin biomacromolecule in the top part of the moso bamboo lead to poor thermal stability.For the bioconversion process,no significant difference was found among all the moso bamboo samples,and the relatively higher hydrolysis efficiency was largely dependent on the low crystallinity of cellulose rather than the degree of lignin biosynthesis.

Deciphering the Enigma of Lignification： Precursor Transport, Oxidation, and the Topochemistry of Lignin Assembly

Plant lignification is a tightly regulated complex cellular process that occurs via three sequential steps： the synthesis of monolignols within the cytosol; the transport of monomeric precursors across plasma membrane; and the oxidative polymerization of monolignols to form lignin macromolecules within the cell wall. Although we have a reasonable understanding of monolignol biosynthesis, many aspects of lignin assembly remain elusive. These include the pre- cursors＇ transport and oxidation, and the initiation of lignin polymerization. This review describes our current knowledge of the molecular mechanisms underlying monolignol transport and oxidation, discusses the intriguing yet least- understood aspects of lignin assembly, and highlights the technologies potentially aiding in clarifying the enigma of plant lignification.

Studies on the lignification of secondary tissue during annual cambium development in Koelreuteria bipinnata

The lignification process in Koelreuteria bipinnata was examined by fluorescence microscopy and histochemical staining.The earlywood vessels,which differentiated from the vascular cambium at an early stage,were the first to begin lignification.There were no fluorescence signals in the tissues surrounding the earlywood vessels.Lignification occurred more rapidly in earlywood vessels than in the surrounding tissues.The cambium became very active during the period from May to July,and the xylem tissue

Altered Lignin Biosynthesis Improves Cellulosic Bioethanol Production in Transgenic Maize Plants Down-Regulated for Cinnamyl Alcohol Dehydrogenase

Cinnamyl alcohol dehydrogenase （CAD） is a key enzyme involved in the last step of monolignol biosynthesis. The effect of CAD down-regulation on lignin production was investigated through a transgenic approach in maize. Trans- genic CAD-RNAi plants show a different degree of enzymatic reduction depending on the analyzed tissue and show alter- ations in cell wall composition. Cell walls of CAD-RNAi stems contain a lignin polymer with a slight reduction in the S-to-G ratio without affecting the total lignin content. In addition, these cell walls accumulate higher levels of cellulose and ara- binoxylans. In contrast, cell walls of CAD-RNAi midribs present a reduction in the total lignin content and of cell wall polysaccharides. In vitro degradability assays showed that, although to a different extent, the changes induced by the repression of CAD activity produced midribs and stems more degradable than wild-type plants. CAD-RNAi plants grown in the field presented a wild-type phenotype and produced higher amounts of dry biomass. Cellulosic bioethanol assays revealed that CAD-RNAi biomass produced higher levels of ethanol compared to wild-type, making CAD a good target to improve both the nutritional and energetic values of maize lignocellulosic biomass.

Transcriptional regulation of fleshy fruit texture

Fleshy fruit texture is a critically important quality characteristic of ripe fruit.Softening is an irreversible process which operates in most fleshy fruits during ripening which,together with changes in color and taste,contributes to improvements in mouthfeel and general attractiveness.Softening results mainly from the expression of genes encoding enzymes responsible for cell wall modifications but starch degradation and high levels of flavonoids can also contribute to texture change.Some fleshy fruit undergo lignification during development and post-harvest,which negatively affects eating quality.Excessive softening can also lead to physical damage and infection,particularly during transport and storage which causes severe supply chain losses.Many transcription factors(TFs)that regulate fruit texture by controlling the expression of genes involved in cell wall and starch metabolism have been characterized.Some TFs directly regulate cell wall targets,while others act as part of a broader regulatory program governing several aspects of the ripening process.In this review,we focus on advances in our understanding of the transcriptional regulatory mechanisms governing fruit textural change during fruit development,ripening and postharvest.Potential targets for breeding and future research directions for the control of texture and quality improvement are discussed.

Genome-wide Expression Profiling in Seedlings of the Arabidopsis Mutant uro that is Defective in the Secondary Cell Wall Formation

Plant secondary growth is of tremendous importance, not only for plant growth and development but also for economic usefulness. Secondary tissues such as xylem and phloem are the conducting tissues in plant vascular systems, essentially for water and nutrient transport, respectively. On the other hand, products of plant secondary growth are important raw materials and renewable sources of energy. Although advances have been recently made towards describing molecular mechanisms that regulate secondary growth, the genetic control for this process is not yet fully understood. Secondary cell wall formation in plants shares some common mechanisms with other plant secondary growth processes. Thus, studies on the secondary cell wall formation using Arabidopsis may help to understand the regulatory mechanisms for plant secondary growth. We previously reported phenotypic characterizations of an Arabidopsis semi-dominant mutant, upright rosette （uro）, which is defective in secondary cell wall growth and has an unusually soft stem. Here, we show that lignification in the secondary cell wall in uro is aberrant by analyzing hypocotyl and stem. We also show genome-wide expression profiles of uro seedlings, using the Affymetrix GeneChip that contains approximately 24 000 Arabidopsis genes. Genes identified with altered expression levels include those that function in plant hormone biosynthesis and signaling, cell division and plant secondary tissue growth. These results provide useful information for further characterizations of the regulatory network in plant secondary cell wall formation.

ABCB1 and ABCB19 auxin transporters have synergistic effects on early and late Arabidopsis anther development

Arabidopsis abcbl abcb19 double mutants defective in the auxin transporters ABCB1/PGP1 and ABCB19/PGP19 are altered in stamen elongation, anther dehiscence and pollen maturation. To assess the contribution of these transporters to stamen development we performed phenotypic, histological analyses, and in situ hybridizations on abcbl and abcbl9 single mutant flowers. We found that pollen maturation and anther dehiscence are precocious in the abcbl but not in the abcb19 mutant. Accordingly, endothecium ligniflcation is altered only in abcbl anthers. Both abcbl and abcb1 abcb19 stamens also show altered early development, with asynchronous anther Iocules and a multilayer tapetum. DAPI staining showed that the timing of meiosis is asynchronous in abcbl abcb19 anther Iocules, while only a small percentage of pollen grains are non- viable according to Alexander＇s staining. In agreement, TAM （TARDY ASYNCHRONOUS MEIOSIS）, as well as BAM2 （BARELY ANY MERISTEM）involved in tapetal cell development--areoverexpressed in abcbl abcb19 young flower buds. Corre- spondingly, ABCB1 and ABCB19 mRNA localization supports the observed phenotypes of abcbl and abcbl abcb19 mutant anthers. In conclusion, we provide evidence that auxin transport plays a significant role both in early and late stamen development： ABCB1 plays a major role during anther development, while ABCB19 has a synergistic role.