Properties and potential applications of natural cellulose fibers from the bark of cotton stalks

Natural cellulose fibers have been obtained from the bark of cotton stalks and the fibers have been used to develop composites. Cotton stalks are rich in cellulose and account for up to 3 times the quantity of cotton fiber produced per acre. Currently, cotton stalks have limited use and are mostly burned on the ground. Natural cellulose fibers obtained from cotton stalks are composed of approximately 79% cellulose and 13.7% lignin. The fibers have breaking tenacity of 2.9 g per denier and breaking elongation of 3% and modulus of 144 g per denier, between that of cotton and linen. Polypropylene composites reinforced with cotton stalk fibers have flexural, tensile and impact resistance properties similar to jute fiber reinforced polypropylene composites. Utilizing cotton stalks as a source for natural cellulose fibers provides an opportunity to increase the income from cotton crops and make cotton crops more competitive to the biofuel crops.     

Ultrastructural effects of cellulose biosynthesis inhibitor herbicide on developing cotton fibers

Summary Cotton fibers are often utilized as a model system to investigate cellulose biosynthesis and cell wall elongation. In this study, we grew cotton fibers in vitro, with ovules dissected at day zero post anthesis as the expiant source, in the presence of three herbicides that inhibit cellulose biosynthesis. Cultures were sampled for electron microscopy and immunocytochemistry 1–2 days after beginning the treatments. After dichlobenil treatment, the fibers were much shorter than the controls and assumed a variety of abnormal shapes, from shortened versions of the control fiber to nearly spherical. The inner layers of the fiber wall often contained juxtaposed electron-translucent and -transparent areas; this layer reacted strongly with antibodies to callose. Cellulase-gold labeling in these newly developed fibers grown in the presence of dichlobenil was present at only about 3% of the control labeling. After treatment with either isoxaben or flupoxam, the fibers assumed spherical shapes and frequently (more than 60% of fibers) exhibited a new cell plate within the fiber, indicating that cell division had occurred, a process that rarely occurred in the controls. Unlike the dichlobenil-treated fibers, fibers grown in the presence of isoxaben or flupoxam contained an extensive accumulation of chiefly deesterified pectins, replacing the entire wall with an elaborated version of the pectin sheath found in control cotton fibers. These data indicate that all three herbicides are effective disrupters of cellulose biosynthesis and cause radical changes in cell wall structure and composition. Moreover, these data indicate that the composition of the walls may influence indirectly cell cycle kinetics, keeping these fiber cells in a more meristematic mode.     

A Comparative Analysis of in vitro cellulose synthesis from cell-free extracts of mung bean (Vigna radiata,Fabaceae) And Cotton (Gossypium hirsutum,Malvaceae)

A comparison of cellulose synthesized in vitro from primary walls of etiolated mung bean (Vigna radiata) seedlings and secondary walls of cotton fibers (Gossypium hirsutum) was made by applying conditions found to be essential for in vitro cellulose I assembly from cotton (Kudlicka et al., 1995, Plant Physiology, vol. 107, pp. 111–123). Mung bean fractions including the plasma membrane (PM), the first solubilized fraction (SE₁), and the second solubilized fraction (SE₂), incorporated more radioactive UDP-Glc into the total product than the same fractions from secondary walls. A significant difference was found with the mild digitonin solubilized fraction (SE₁), which produced eight times more total product than the SE₁ fraction of cotton. However, the SE₁ fraction from cotton produced a larger quantity of cellulose (32.1%) than from mung bean (6.9%). Treatment of the in vitro product by acetic/nitric acid reagent (AN) for varying periods of time demonstrated that cellulose synthesized in vitro from mung bean was more easily degraded than cellulose from cotton fibers. This would suggest that cellulose I produced in vitro from the cotton SE₁ fraction may have a higher crystallinity and DP than cellulose I produced in vitro from mung bean. The fibrils of cellulose produced by the SE, fraction of mung bean were loosely associated and not arranged into a compact bundle as in case of cellulose I synthesized by the cotton SE₁ fraction. The electron diffraction patterns (ED) of both products show reflections characteristic for cellulose I. Products from the SE₂ fraction of mung bean and cotton reveal similarities with the cellulose II allomorph synthesized, as well as abundant β-1,3-glucan.     

Longevity and egg development of adult female boll weevils fed exclusively on different parts and stages of cotton fruiting bodies

The capacities of the rind (i.e., the developing calyx and petals of squares; and the outer casing, or husk, of bolls) and the internal reproductive portion of cotton, Gossypium hirsutum L. (Malvaceae), squares of three sizes, and bolls of three ages to influence adult female boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), longevity and egg production were evaluated in laboratory bioassays. While feeding on the reproductive portion of squares was expected to support adult boll weevils for considerable periods of time (e.g., medium square reproductive portion: ≈185 days), feeding on rinds also resulted in substantial longevity (e.g., medium square rind: ≈120 days). As anticipated, feeding on the reproductive portion of squares resulted in formation of chorionated eggs in mated females, but a diet comprised exclusively of rinds, particularly from large squares, was associated with gravidity and high fecundity relative to rinds of young and mature bolls. The reproductive portion and rind of post‐bloom and young bolls as sources of food resulted in limited gravidity while mature bolls were not associated with any egg formation. These findings further our understanding of how boll weevils feed on different parts of the cotton plant and how those parts as food sources are related to the biology and ecology of the boll weevil.     

氮素对不同开花期棉铃纤维比强度形成的生理基础的影响

于2005年在江苏南京(长江流域下游棉区)和徐州(黄河流域黄淮棉区)棉田设置不同氮素水平(零氮：0 kg N·hm^-2,适氮：240 kg N·hm^-2,高氮：480 kg N·hm^-2)试验,研究氮素对不同开花期棉铃(伏前桃、伏桃和秋桃)纤维比强度形成生理基础的影响.结果表明：与适氮处理相比,零氮处理显著降低了棉铃对位叶氮浓度,增加了C/N,影响程度随开花期的推迟而加大,导致伏桃、秋桃对位叶制造和运输光合产物的能力在棉铃发育中后期大幅度下降,棉纤维的相对生长速率以及纤维发育关键酶蔗糖合成酶和β-1,3-葡聚糖酶活性降低,纤维素快速累积持续期缩短,纤维比强度显著降低;高氮处理显著增加了棉铃对位叶氮浓度,降低了C/N,影响程度随开花期的推迟而降低,其降低了伏前桃、伏桃发育过程中光合产物向纤维分配的比例、棉铃发育前中期的纤维发育关键酶活性及纤维素累积速率,导致其纤维比强度亦显著降低.综合分析认为,适宜的施氮量可以协调棉花的“源库”关系,有利于促进不同开花期棉铃高纤维比强度的形成.与适氮处理相比,零氮处理的伏前桃、伏桃和秋桃纤维比强度分别降低了1.8%、5.8%和13.0%,高氮处理则分别降低了8.2%、7.4%和-2.4%.     

Changes in biochemical composition of the cell wall of the cotton fiber during development

The composition of the cell wall of the cotton fiber (Gossypium hirsutum L. Acala SJ-1) has been studied from the early stages of elongation (5 days postanthesis) through the period of secondary wall formation, using cell walls derived both from fibers developing on the plant and from fibers obtained from excised, cultured ovules. The cell wall of the elongating cotton fiber was shown to be a dynamic structure. Expressed as a weight per cent of the total cell wall, cellulose, neutral sugars (rhamnose, fucose, arabinose, mannose, galactose, and noncellulosic glucose), uronic acids, and total protein undergo marked changes in content during the elongation period. As a way of analyzing absolute changes in the walls with time, data have also been expressed as grams component per millimeter of fiber length. Expressed in this way for plant-grown fibers, the data show that the thickness of the cell wall is relatively constant until about 12 days postanthesis; after this time it markedly increases until secondary wall cellulose deposition is completed. Between 12 and 16 days postanthesis increases in all components contribute to total wall increase per millimeter fiber length. The deposition of secondary wall cellulose begins at about 16 days postanthesis (at least 5 days prior to the cessation of elongation) and continues until about 32 days postanthesis. At the time of the onset of secondary wall cellulose deposition, a sharp decline in protein and uronic acid content occurs. The content of some of the individual neutral sugars changes during development, the most prominent change being a large increase in noncellulosic glucose which occurs just prior to the onset of secondary wall cellulose deposition. Methylation analyses indicate that this glucose, at least in part, is 3-linked. In contrast to the neutral sugars, no significant changes in cell wall amino acid composition are observed during fiber development.     

Natural cellulose fibers from switchgrass with tensile properties similar to cotton and linen

We report the production and characteristics of natural cellulose fibers obtained from the leaves and stems of switchgrass. In this paper, the composition, structure and properties of fibers obtained from the leaves and stem of switchgrass have been studied in comparison to the common natural cellulose fibers, such as cotton, linen and kenaf. The leaves and stems of switchgrass have tensile properties intriguingly similar to that of linen and cotton, respectively. Fibers were obtained from the leaves and stems of switchgrass using a simple alkaline extraction and the structure and properties of the fibers were studied. Fibers obtained from switchgrass leaves have crystallinity of 51%, breaking tenacity of 5.5 g per denier (715 MPa) and breaking elongation of 2.2% whereas the corresponding values for fibers obtained from switchgrass stems are 46%, 2.7 g per denier and 6.8%, respectively. Switchgrass is a relatively easy to grow and high yield biomass crop that can be source to partially substitute the natural and synthetic fibers currently in use. We hope that this research will stimulate interests in using switchgrass as a novel fiber crop in addition to being promoted as a potential source for biofuels.     

Changes in the level of tubulin subunits during development of cotton (Gossypium hirsutum) fiber

The levels of tubulin protein in developing cotton ( Gossypium hirsutum L. cv. Stoneville 825) fibers were measured from 8 to 28 days post-anthesis using commercially available monoclonal antibodies against alpha- and beta-tubulin. As the monoclonal antibodies against alpha- and beta-tubulin were prepared from yeast tubulin and chick brain tubulin, respectively, indirect immunofluorescence microscopy was used to establish that the two monoclonal antibodies recognized microtubule structures in cotton fibers. Western blots of electrophoretically separated proteins in crude extracts of cotton roots and fibers showed that single polypeptides with the expected apparent molecular weight for tubulin subunits were recognized by the antisera. An enzyme-linked immunosorbent assay was used to quantify tubulin levels. From 10 to 20 days post-anthesis the level of tubulin protein increases approximately three-fold. After 20 days post-anthesis, the amount of tubulin relative to total fiber protein reaches a plateau or decreases slightly. The rapid rise in tubulin is correlated with the elongation of the fiber and an increase in cellulose synthesis.     

Effects of some organic solvents on ethylene evolution from young cotton bolls

The presence of promoter(s) of ethylene biosynthesis in young cotton (Gossypium hirsutum L.) fruits (bolls) was demonstrated by injection of an aqueous extract from bolls into other bolls and measurement of a 3-fold increase in rate of ethylene evolution. Injection of methionine did not affect rate of ethylene production, indicating that the promoter extracted from bolls was not methionine. Injection of the ethoxy analog of rhizobitoxine inhibited ethylene production, indicating that methionine is a precursor of ethylene in cotton bolls. Injection of organic solvents altered membrane permeability, as indicated by decreased resistance to electric current at 1,000 Hz, and stimulated ethylene evolution. The less polar solvents caused large increases in ethylene evolution, major loss of resistance, and visible evidence of membrane damage. The results support the hypothesis that membrane integrity affects rate of ethylene biosynthesis.     

Presence of Aspergillus flavus in developing cotton bolls and its relation to contamination of mature seeds

Aspergillus flavus spores were dusted onto the involucral nectaries of cotton flowers. The fungus was present in 20 to 58% of the immature bolls harvested 25 or 35 days after anthesis. Among similarly inoculated bolls fully matured either in the field or under sterile conditions at ambient temperatures after excision from the plants, only 3 to 14% contained A. flavus in the seeds. There was no significant difference in the numbers of contaminated bolls between the excised and field-matured treatments. It is concluded that A. flavus is present in developing cotton bolls before dehiscence, but its presence does not ensure infection of mature seeds, and that excision does not reduce A. flavus contamination if the bolls are maintained at ambient temperatures.     

Presence of Aspergillus flavus in developing cotton bolls and its relation to contamination of mature seeds.

Aspergillus flavus spores were dusted onto the involucral nectaries of cotton flowers. The fungus was present in 20 to 58% of the immature bolls harvested 25 or 35 days after anthesis. Among similarly inoculated bolls fully matured either in the field or under sterile conditions at ambient temperatures after excision from the plants, only 3 to 14% contained A. flavus in the seeds. There was no significant difference in the numbers of contaminated bolls between the excised and field-matured treatments. It is concluded that A. flavus is present in developing cotton bolls before dehiscence, but its presence does not ensure infection of mature seeds, and that excision does not reduce A. flavus contamination if the bolls are maintained at ambient temperatures.     

The rate of cellulose increase is highly related to cotton fibre strength and is significantly determined by its genetic background and boll period temperature

This experiment was conducted to study the relationship between the increase in cellulose content in developing cotton bolls and their final cotton fibre strength. The rate of cellulose increase over time was estimated using logistical regression, and the logistic equation parameters were then used to compare different cotton cultivars in different temperature environments. The increase in cellulose content followed a typical “S” curve, with the boll period time divided into slow-fast-slow stages. In different cultivars, the final fibre strength was closely related to the characters of the fast cellulose content increasing stage, negatively related to the maximal cellulose increasing rate (P < 0.05), and positively related to the duration of the fast cellulose content increasing stage (P < 0.01). In the same cultivar, low temperature reduced the maximal cellulose increasing rate and prolonged the duration of the fast cellulose increasing stage. The results indicate that, in diverse genetic background, long-lasting and tempered cellulose growth during the rapid cellulose increasing stage is of significant benefit to high strength fibre development. For closely related cotton cultivars, decreasing the maximal cellulose increasing rate and the termination of rapid cellulose increasing stage reduced fibre strength that often occurs when temperatures are low.     

Biotechnological improvement of cotton fibre maturity

This mini-review focuses on the prospects and tools for controlling cotton fibre secondary wall thickness. Cotton fibre secondary walls are composed of almost 100% cellulose, and are responsible for fibre maturity and a large component of fibre yield. Improved fibre yield and maturity would result from the ability to control secondary wall cellulose deposition quantitatively, including making the process less sensitive to environmental stress. Both genetic engineering and marker-assisted breeding are possible avenues for effecting such improvements, but first key genes that participate in the regulation and control of secondary wall cellulose biogenesis must be identified. Recent advances towards understanding and manipulating cotton fibre secondary wall deposition that are discussed here include: (i) experimental approaches to identify metabolic participants in cellulose biogenesis; (ii) isolation and characterization of promoters to drive foreign gene expression preferentially during secondary wall deposition; and (iii) a novel set of cDNA sequences representing genes that are differentially expressed during cotton fibre secondary wall deposition compared with primary wall deposition.     

Electron microscopy of the cotton fibre: new observations on cell wall formation.

The ultrastructure of the cotton fibres was examined after developing successful fixation methods. Fibre cells were fixed at different stages of development. In cells which were elongating and producing primary cell walls, the Golgi apparatus appeared to be directly involved in secretion and synthesis of primary wall components. In cells which were synthesizing thick secondary cell walls, evidence suggested a major role for the endoplasmic reticulum and plasma memebrane in the synthesis and secretion of secondary wall materials. The possibility of a shift from a Golgi apparatus pathway for primary wall synthesis to an endoplasmic reticulum pathway for secondary wall synthesis is discussed. Plasma membrane micro-invaginations are present only during secondary wall synthesis and may represent sites of cellulose assembly. A model for primary wall biogenesis via the Golgi apparatus is presented, and the potential of the cotton fibre as a model system for studying cellulose biogenesis in higher plants is discussed.     

Analysis of cell-wall polymers during cotton fiber development

Although the fibers of cotton (Gossypium hirsutum L.) are single cells with a secondary wall composed primarily of cellulose, the cell-wall polymers of the fibers are technically difficult to characterize with respect to molecular weights. This limitation hinders understanding how the fiber wall composition changes during development, particularly with respect to genotypic variations, and how the molecular composition is related to physical properties. We analyzed cell-wall polymers from cotton fibers (cultivar, Texas Marker-1) at several developmental stages (8–60 days post-anthesis; DPA) by gel-permeation chromatography of components soluble in dimethyl acetamide and lithium chloride. This procedure solubilizes fiber cell-wall components directly without prior extraction or derivatization, processes that could lead to degradation of high-molecular-weight components. Cellwall polymers from fibers at primary cell-wall stages had lower molecular weights than the cellulose from fibers at the secondary wall stages; however, the high-molecularweight cellulose characteristic of mature cotton was detected as early as 8 DPA. High-molecular-weight material decreased during the period of 10–18 DPA with concomitant increase in lower-molecular-weight wall components, possibly indicating hydrolysis during the later stages of elongation.Abbreviations DMAC dimethyl acetamide - DP degree of polymerization - DPA days post anthesis - GPC gel-permeation chromatography - MW molecular weight - MWD molecular-weight distribution - TM-1 Texas Marker 1     

Oviposition on and mining in bolls of Bt and non-Bt cotton by resistant and susceptible pink bollworm (Lepidoptera: Gelechiidae)

Transgenic cotton that produces insecticidal crystal protein Cry1Ac of Bacillus thuringiensis (Bt) has been effective in controlling pink bollworm, Pectinophora gossypiella (Saunders). We compared responses to bolls of Bt cotton and non-Bt cotton by adult females and neonates from susceptible and Cry1Ac-resistant strains of pink bollworm. In choice tests on caged cotton plants in the greenhouse, neither susceptible nor resistant females laid fewer eggs on Bt cotton bolls than on non-Bt cotton bolls, indicating that the Bt toxin did not deter oviposition. Multiple regression revealed that the number of eggs laid per boll was negatively associated with boll age and positively associated with boll diameter. Females also laid more eggs per boll on plants with more bolls. The distribution of eggs among bolls of Bt cotton and non-Bt cotton was clumped, indicating that boll quality rather than avoidance of previously laid eggs was a primary factor in oviposition preference. Parallel to the results from oviposition experiments, in laboratory no-choice tests with 10 neonates per boll, the number of entrance holes per boll did not differ between Bt cotton and non-Bt cotton for susceptible and resistant neonates. Also, like females, neonates preferred younger bolls and larger bolls. Thus, acceptance of bolls by females for oviposition and by neonates for mining was affected by boll age and diameter, but not by Bt toxin in bolls. The lack of discrimination between Bt and non-Bt cotton bolls by pink bollworm from susceptible and resistant strains indicates that oviposition and mining initiation are independent of susceptibility to Cry1Ac.