Xylans from the tropical grass Panicum maximum

Two xylans have been isolated from the mature tissues of the tropical grass Panicum maximum—an arabino(4-O-methylglucurono)xylan and an acidic galactoarabinoxylan. Both consist of a main chain of β(1 → 4) linked d-xylopyranosyl residues. The former has average of ca 46 such residues to which are attached ca 7 l-arabinofuranosyl and (ca 2 4-O-methyl-d-glucopyranuronosyl residues at C3 and C2 positions respectively. The acidic galactoarabinoxylan has a $\text{DP}$_n of ca 90 and contains arabinose, galactose, xylose and uronic acid residues in the molar ratio 10:5:22:4. Methylation analysis and periodate oxidation indicated the highly branched nature of this polysaccharide.     

Uronic acid residues in the total hemicelluloses of oats

A new method for the estimation of uronic acid residues is described. The changes in total hemicellulose composition of the leaf and stem tissues of field-grown oat plants have been further examined. In any one such tissue, increased plant maturity is accompanied by an increase in the percentage of xylose residues and by decreases in the percentages of arabinosyl, glucosyl, and uronosyl residues. The ratio of 4-O-methyl-D-glucuronosyl to D-glucuronosyl residues increases with maturity.     

Fractionation of hemicelluloses from maize cell walls with increasing concentrations of alkali

Hemicelluloses were solubilized from depectinated walls of maize coleoptiles and leaves with increasing concentrations of alkali to yield three major fractions of polymers. A highly-substituted glucuronoarabinoxylan released by dilute alkali from walls of coleoptiles was present only in very small amounts in the walls of the leaves. The stepwise extractions with increasing concentrations of alkali resolved a relatively unbranched xylan from a mixture of mixed-linked glucan, xyloglucan and additional xylan from walls of young leaves. Delignification in acidic sodium chlorite solubilized a small amount of substituted xylan from walls of both coleoptiles and leaves, and rendered about one-half of the unextracted hemicellulose soluble in only 0.02 M potassium hydroxide solution. Delignification prevented the detection of highly-substituted xylans released by dilute alkali.     

Aqueous extraction of sugarcane bagasse hemicellulose and production of xylose syrup

At the optimum level of severity, the aqueous extraction of sugarcane bagasse, an abundant agricultural resdue, gave, depending on the degree of comminution, 60% to 89% yield of xylose, most of it in the form of a water soluble xylan. A process for producing xylose-rich syrups was conceived and tested, consisting of aqueous extraction, acid hydrolysis of the concentrated aqueous extract centrifugal clarification of the hydrolysate, and recovery of the acid by continuous ion exclusion. The cost estimate indicates operating costs on the order of $0.12 to $0.15/kg xylose, in the form of xylose-rich molasses. (c) 1995 John Wiley & Sons, Inc.     

Isolation and characterization of xylose- and xylan-utilizing anaerobic bacteria

By enrichment with xylose, nine mesophilic strains of anaerobic bacteria were obtained from various sources. Two isolates appear to belong to the genus Eubacterium. Six other strains belong to the genus Clostridium. Three of the isolated strains utilized larch wood xylan. The percentage of utilization of xylose and xylan and the yield of fermentation end products — viz. acetic acid and butyric acid-are equivalent to that of Clostridium acetobutylicum (ATCC 824) and reported thermophilic strains.     

矮牵牛叶肉原生质体再生壁多糖的形成及转化

用~3H—葡萄糖饲喂矮牵牛叶肉原生质体,发现放射性集中在半纤维素部分,占整个再生壁的83％～90％,而纤维素中约占9％。纸层析分析证明,葡萄糖占半纤维素部分中性糖总量的70％,再生壁主要是由非纤维素葡聚糖组成。原生质体在含有~3H—葡萄糖的培养基中培养4d后,24h追踪表明,部分半纤维素转化成纤维素。加入香豆素,至少3d之内抑制半纤维素向纤维素转化;除去抑制剂,半纤维素含量迅速降低而纤维素增加。所以认为矮牵牛叶向原生质体壁再生过程中半纤维素是合成纤维素的前体。     

Chitosan production from hemicellulose hydrolysate of corn straw: impact of degradation products on Rhizopus oryzae growth and chitosan fermentation

Aims: To examine the potential use of hemicellulose hydrolysate (HH) for the production of chitosan by Rhizopus oryzae and investigate the influence of contents in HH on mycelia growth and chitosan synthesis. Methods and Results: Compared to xylose medium, HH enhanced mycelia growth, chitosan content and production of R. oryzae by 10·2, 64·5 and 82·1%, respectively. During sulfuric acid hydrolysis of corn straw, sugars (glucose, galactose, etc) and inhibitors (formic acid, acetic acid and furfural) were generated. Acetic acid (2·14 g l^?1) and formic acid (0·83 g l^?1) were stimulative, while furfural (0·55 g l^?1) was inhibitory. Inhibitors, at different concentrations, increased the mycelia growth and chitosan production by 24·5–37·8 and 60·1–207·1%. Conclusions: HH of corn straw is a good source for chitosan production. Inhibitors in HH, at proper concentrations, can enhance chitosan production greatly. Significance and Impact of the Study: This work for the first time reported chitosan production from HH. Chitosan production can be greatly enhanced by cheap chemicals such as inhibitors in HH.     

Phosphorus deficiency enhances aluminum tolerance of rice (Oryza sativa) by changing the physicochemical characteristics of root plasma membranes and cell walls

The negative charge at the root surface is mainly derived from the phosphate group of phospholipids in plasma membranes (PMs) and the carboxyl group of pectins in cell walls, which are usually neutralized by calcium (Ca) ions contributing to maintain the root integrity. The major toxic effect of aluminum (Al) in plants is the inhibition of root elongation due to Al binding tightly to these negative sites in exchange for Ca. Because phospholipid and pectin concentrations decrease in roots of some plant species under phosphorus (P)-limiting conditions, we hypothesized that rice (Oryza sativa L.) seedlings grown under P-limiting conditions would demonstrate enhanced Al tolerance because of their fewer sites on their roots. For pretreatment, rice seedlings were grown in a culture solution with (+P) or without (−P) P. Thereafter, the seedlings were transferred to a solution with or without Al, and the lipid, pectin, hemicellulose, and mineral concentrations as well as Al tolerance were then determined. Furthermore, the low-Ca tolerance of P-pretreated seedlings was investigated under different pH conditions. The concentrations of phospholipids and pectins in the roots of rice receiving −P pretreatment were lower than those receiving +P pretreatment. As expected, seedlings receiving the −P pretreatment showed enhanced Al tolerance, accompanied by the decrease in Al accumulation in their roots and shoots. This low P-induced enhanced Al tolerance was not explained by enhanced antioxidant activities or organic acid secretion from roots but by the decrease in phospholipid and pectin concentrations in the roots. In addition, low-Ca tolerance of the roots was enhanced by the −P pretreatment under low pH conditions. This low P-induced enhancement of low-Ca tolerance may be related to the lower Ca requirement to maintain PM and cell wall structures in roots of rice with fewer phospholipids and pectins.     

Comprehensive Compositional Analysis of Plant Cell Walls (Lignocellulosic biomass) Part II: Carbohydrates

The need for renewable, carbon neutral, and sustainable raw materials for industry and society has become one of the most pressing issues for the 21st century. This has rekindled interest in the use of plant products as industrial raw materials for the production of liquid fuels for transportation² and other products such as biocomposite materials⁶. Plant biomass remains one of the greatest untapped reserves on the planet⁴. It is mostly comprised of cell walls that are composed of energy rich polymers including cellulose, various hemicelluloses, and the polyphenol lignin⁵ and thus sometimes termed lignocellulosics. However, plant cell walls have evolved to be recalcitrant to degradation as walls contribute extensively to the strength and structural integrity of the entire plant. Despite its necessary rigidity, the cell wall is a highly dynamic entity that is metabolically active and plays crucial roles in numerous cell activities such as plant growth and differentiation⁵. Due to the various functions of walls, there is an immense structural diversity within the walls of different plant species and cell types within a single plant⁴. Hence, depending of what crop species, crop variety, or plant tissue is used for a biorefinery, the processing steps for depolymerisation by chemical/enzymatic processes and subsequent fermentation of the various sugars to liquid biofuels need to be adjusted and optimized. This fact underpins the need for a thorough characterization of plant biomass feedstocks. Here we describe a comprehensive analytical methodology that enables the determination of the composition of lignocellulosics and is amenable to a medium to high-throughput analysis (Figure 1). The method starts of with preparing destarched cell wall material. The resulting lignocellulosics are then split up to determine its monosaccharide composition of the hemicelluloses and other matrix polysaccharides1, and its content of crystalline cellulose⁷. The protocol for analyzing the lignin components in lignocellulosic biomass is discussed in Part I³.