Exploration Of Fiber Differentiation And Development And Pigment Component In Colored Cotton

Brown and green are the two most common fiber colors in colored cotton cultivars(Gossypium hirsutum L.). Although there are drawbacks to colored cotton, such as poorquality and the instability of the fiber pigments, colored cotton remains widely popularbecause it is environment-friendly, economical, and beneficial to human health. In order toexplore the formation of fiber pigment and the relationship between fiber pigment and fiberquality and color stability in colored cotton cultivars, the experiments were conducted withdifferent cotton cultivars, including brown cotton cultivars (ZX-1and XC-1), green cottoncultivars (G-7and4560), and white cotton cultivar (LMY28). The regulation of fiberdifferentiation and development and the related metabolism of physiological and biochemical,the dynamic changes of supramolecular structure and fiber color, as well as, the distributionand composition of fiber pigments in fiber development process of colored cotton weresystematic studied by the combining methods of morphology, physiological and biochemicalmeasurements, and metabolomics. The main results were as follows.1Patterns of color formation in different fibers during development of colored cottoncultivarsThe fiber color of brown cultivars gradually deepened before35days post anthesis(DPA), rapidly deepened from35DPA to40DPA, and from55DPA to maturation, whilegreen cultivars gradually deepened from25DPA to45DPA, reached a maxima at45DPA,and then faded from55DPA to maturation.2Regulation of pigment deposition in colored cotton fibers during developmentPigment forming time and depositing position showed significant differences in thefibers development process of ZX-1and G-7’s. That is to say, the pigment formation of G-7isearlier than that of ZX-1, and the pigment of G-7deposited in both lumen and the innersecondary wall, while the pigment of ZX-1only deposited in lumen. 3Mechanism of fiber quality formation in colored cotton cultivars3.1Regulation of differentiation in colored cotton fiberThe central part of the ovule epidermal cells began to differentiate at1DPA. There wereprotuberances of ovule fiber cells at0DPA. The number and volume of protuberancesincreased at1DPA, when the fiber cells of LMY28had the elongated trends. In addition,fiber cells already elongated at3DPA. In summary, LMY28was the best, followed by ZX-1,and G-7was the worst in the degree of differentiation, the number of protuberance, and thelevel of development and elongation.3.2Fiber quality formation of colored cotton cultivarsFiber length,3.2mm gauge strength, fiber maturation and fiber micronaire was increasedwith the development of the cotton fiber. The results showed that the ultimate fiber length,fiber3.2mm gauge tenacity, fiber maturation and fiber micronaire of all cotton cultivarsranked as LMY28> ZX-1and XC-1> G-7and4560.3.3Relationship between super-molecular structure changes and fiber quality in fiberdevelopment process of colored cotton cultivarsThe corresponding crystalline grain size increased constantly and orientation parametersdiminished gradually in fiber development process, but there were differences amongdifferent cultivars. The crystalline grain size had a correlation with3.2mm gauge tenacity (r=0.8962*), as well as, the orientational distribution angle-ψ () a nd spiral angle-φ () had anegative correlation with fiber3.2mm gauge tenacity, fiber maturation and fiber micronaire(r=0.9382*to0.9023*), moreover, the orientational separate angle-α () had a negativecorrelation with fiber length (r=0.9731**). In conclusion, the poor quality of colored cottonfiber is probably in relation to poor fiber3.2mm gauge tenacity, fiber maturation, fibermicronaire, fiber length, resulting from low initial value and termination value of crystallinegrain size and high termination value of orientation parameters in fiber development process.3.4The relationship between cellulose content and the contents of sugars and mineralsduring fiber development in colored cotton cultivarsCellulose contents during fiber development changed along S-shaped curves among thetested cotton cultivars. The cellulose content was significantly higher in the white cottoncultivar LMY28than in the colored cotton cultivars ZX-1and G-7after25DPA. Sugar and mineral contents showed significant changes during fiber development. Fructose, glucose,galactose, cellobiose, nitrogen, phosphorus, potassium, sulfur, and magnesium contents wereessential for cellulose deposition during fiber development. In this study, glucose was shownto be a direct precursor and key sugar in cellulose biosynthesis in cotton cultivars. There maybe a special mechanism in colored cotton cultivars that greater amounts of total carbohydrates,especially glucose, and minerals (nitrogen, phosphorus, potassium, sulfur, and magnesium)were consumed by the biosynthesis and deposition of fiber pigments than in the biosynthesisof cellulose. This finding could explain why the cellulose content was significantly lower inthe colored cotton cultivars than in white cotton.3.5The activity changes for enzymes associated with fiber development in coloredcotton cultivarsThe activity of enzymes associated with fiber development (sucrose synthase, β-1,3-glucanase, invertase, indoleasetic acid oxidase, and peroxidase) in colored cotton cultivarswere less than in white cotton cultivar. Effecting the cellulose biosynthesis and the formationof fiber quality of colored cotton. In addition, the activity of sucrose phosphate synthase incolored cotton cultivars was higher than in white cotton cultivar. As well as, the cellulosecontent of colored cotton was lower than white cotton, may be the sucrose was used for thefiber pigment biosynthesis, causing the short supply of energy in the process of the cellulosebiosynthesis. Resulting in the cellulose content in colored cotton was lower than white cottonand affecting the fiber quality formation in colored cotton.4The fiber pigment composition in colored cottonAccording to the extraction method and the separation and detection of component, wefound the best fiber pigment was extracted48h by Soxhlet extraction of methanol in waterbath at80°C. Fiber pigment in different colored cotton cultivars were separated, identified,and quantified by a high-performance liquid chromatographic method with photodiode arrayand mass spectrometric detection (LCMS). Compound of fiber pigment are flavonoids inbrown cotton ZX-1and green cotton G-7, including7compound and12compound,respectively. Seven compounds were identified by LCMS in brown cotton ZX-1, as follows.Leucodelphinidin3-O-(β-D-glucopyranosyl-(1â†'4)-α-L-rhamnopyranoside), Kaempferol3-(3’’-acetyl-α-L-arabinofuranoside)-7-rhamnoside, Rutin, Quercetin, Piscerythramine,Apigenin7-(6’’-crotonylglucoside), Pendulin. Twelve compounds including Pectolinarigenin7-rutinoside, Quercetin3-sulfate-7-α-arabinopyranoside, Epigallocatechin5,3’,5’-trimethyl ether3-O-gallate, Kaempferol3-[6’’-(3-hydroxy-3-methylglutaryl) glucoside], Biochanin A7-O-rutinoside, Quercetin3,3’-dimethylether4’-isovalerate, Isokaempferide7-rutinoside, Apigenin7-(2’’-glucosyllactate),Kaempferol3-(3’’,4’’-diacetylglucoside), Quercetin3-xyloside-7-glucoside, Isorhamnetin3-O-β-D-2’’,3’’,4’’-triacetylglucopyranoside, and Cassiaoccidentalin A, were identified by LCMS ingreen cotton G-7. Meanwhile, the compound1and compound5was colorless, the othercompounds were grayish yellow to yellow of pigment composition in brown cotton ZX-1; thecompound3and compound5was colorless, the other compounds were grayish yellow toyellow of pigment composition in green cotton G-7, respectively. That is to say, the fibercolor of colored cotton may depend on the combination fiber pigment composition andminerals, as well as, the cytoplasmic pH value in fiber cells.