Relationship Between Physiological Characteristic During Cotton Fiber Thickening And Fiber Strength Formation

Fiber strength is an important criterion of cotton quality and the secondary wallthickening stage is a key period to its formation. The study on physiologicalmechanism of cellulose synthesis in cotton fiber has obvious implication forimproving physiological ways to adjust fiber quality and cultivating new excellentbreeds with high fiber strength. By using three cotton genotypes (four cultivars:KC-1(27.2cN/tex), AC-33B(24.0～25.0cN/tex), SC-1(21.2cN/tex)/SC-15(19.5cN/tex))with great difference in fiber strength as materials, field experiments were carried outin Nanjing, Jiangsu Province (cotton belts in lower basin of the Yangtze River) in2004-2005. The study focused on: (1) the relationship between dynamic changes ofthe C/N ratio, internal source protective enzyme activity in leaf subtending boll andboll weight formation; (2) the relationship between dynamic changes of relatedenzyme activities (sucrose synthetase,β-1,3-glueanase, peroxidase and IAA oxidase)during the cotton fiber thickening and fiber strength formation; (3) the relationshipbetween dynamic changes of related matters (soluble sugar, sucrose andβ-1,3-glucan)content, key enzymes (sucrose synthetase andβ-1,3-glucanase) activity during thecotton fiber thickening and fiber strength formation. (4) the relationship betweenphysiological characteristics during fiber thickening and fiber strength formation inCotton seasonal boll.The main results were as follows:1. Relationship between physiological characteristics of the leaf subtendingcotton boll and boll weight formation(1) Genotypic difference of physiological characteristics in leaf subtending boll andits relationship with boll weight formation. By using four cotton cultivars, thedynamic changes of C/N ratio, soluble protein content, internal source protective enzyme activity in the leaf corresponding boll after anthesis were analyzed. Resultsshowed that the leaves corresponding bolls of SC-15 and KC-1 had more activenitrogen metabolism and higher soluble protein content after anthesis, higher activityof internal source protective enzymes, and longer duration of function. Thesephenomena led the longer period taking for rapid increasing of boll weight, higherfiber weight in single boll and higher final boll weight. On the contrary, the leafcorresponding boll of DSC-1 had shorter duration of function, and lowerphysiological activities including higher C/N ratio, sharp drop of internal sourceprotective enzymes activity and higher extent of lipid peroxidation. These itemscaused the shorter period taking for rapid increasing of boll weight, lower speed forfiber weight increasing, and lower final boll weight. The items in AC-33B werebetween above two types. From above results, we suggested that the difference of thephysiological characteristic in leaf corresponding boll might cause the different bollweight formation.(2) Difference of physiological characteristic in leaf subtending cotton seasonalboll and its relationship with boll weight formation. By using four cotton cultivars,the dynamic changes of soluble protein and internal source protective enzyme (SOD,POD, CAT) activities in leaf subtending cotton seasonal boll were analyzed. Bollsamples were labeled on anthesis day (Jul 15, Jul 25, Aug 25 and Sep 10, respectively)and expressed as PSB (pre-summer boll), SB (summer boll), EAB (early autumn boll)and LAB (late autumn boll), respectively. Result showed that the leaves subtendingSB had high physiological activity during the boll development, especially inmid-late stage. It was showed concretely that the content of soluble protein decreasedslowly, the activities of internal source protective enzyme were high, and the leaveshad long function duration. All these might cause the long period taking for rapidincreasing of boll weight, fast speed of boll weight increasing and high boll weight.On the contrary, the leaves subtending LAB had low physiological activity during theboll development. It was showed concretely that the content of soluble proteindecreased quickly and the activities of internal source protective enzyme were low,and the leaf senescence was accelerated. All these might cause the short period takingfor rapid increasing of boll weight, development of fiber and cottonseed in bollrestrained and low boll weight. The characteristics of leaf physiology and boll weightof EAB and PSB were intervenient, while the characteristic of the leaf subtendingEAB were better than the one of PSB. As a conclusion, under different environment and physiological age of cotton plant, Cotton seasonal boll had lots of differences inphysiological activity in leaf subtending boll, which had important effect on thedifferent formation of cotton fiber, cottonseed and boll weight.2. Relationship between activity of enzymes associated with cotton fiberdevelopment and cellulose deposition, fiber strength formationBy choosing three cotton genotypes with significant differences in fiber strengthas materials, the dynamic changes of related enzyme activity and its relationship withcellulose accumulation and fiber strength formation were studied. The results showedthatβ-1,3-glucanase activity continuously decreased and the activities of enzyme(sucrose synthetase, POD and IAA oxidase) had a certain synergistic effect and thecurves were all single peak curves during the secondary wall thickening in cottonfiber. Meanwhile, there were obviously differences among three genotypes in thelevel of enzyme activity and occurrence time of the curve peak. The cultivar (KC-1)with high strength fiber, had higher peak value of the related enzyme (sucrosesynthetase,β-1,3-glucanase, POD and IAA oxidase) activities, and slower descendtrend subsequently. These resulted in a longer and more tempered celluloseaccumulation, and wider range and longer period of fiber strength increasing. In thecultivars (DSC-1 and SC-15) with lower strength fibers, the items were just thecontrary. In the cultivar (AC-33B) with medium strength fiber, the items wereintervenient. In conclusion, significant difference in the related enzymes activityamong different genotypes was detected, and that might be one of the importantfactors which lead to the great difference in the characteristics of celluloseaccumulation and the fiber strength formation in different cotton genotypes.3. Relationship between related matter transform, dynamic changes of keyenzymes activity during cotton fiber thickening and fiber strength formationBy using three cotton genotypes (four cultivars) with significant difference infiber strength as materials, the related matter transformation, key enzyme activity,cellulose accumulation and fiber strength formation were investigated. The resultsshowed that the genotype with high strength fiber (KC-1 was representative cultivar)had more soluble sugar transformed, higher peak ofβ-1,3-glucan content at the onsetof fiber secondary wall thickening. Sucrose synthetase andβ-1,3-glucanase, playsvery important roles in fiber development, always kept in higher activity in KC-1 than ??in other tested culfivars during the fiber secondary wall thickening. All these resultedin longer time and more tempered cellulose accumulation and higher strength fiberformation. On the contrary, the genotype with lower strength fiber (DSC-1 and SC-15were representative culfivars) had less soluble sugar transformed, lower peak ofβ-1,3-glucan content at the onset of fiber seondary wall thickening, slowerincreasing trend of the key enzymes activity and a more quickly descended trendaiterward, leading to a shorter term and rapid cellulose accumulation and lowerstrength fiber. DSC-1, an early cultivar, reached the peak values ofβ-1,3-glucancontent and key enzymes activities earlier than other cultivars for about a week. Andthe starting time of cellulose rapid accumulation was also earlier than other testedcultivars. The characters of the genotype with medium strength fiber (AC-33B) wereintermediate. From above results, we suggested that the differences of the dynamicchanges of soluble sugar andβ-1,3-gluean contents and sucrose synthetase andβ-1,3-glucanase activities might be one of the physiological reasons for thedifferences in the cellulose accumulation and fiber strength formation. Further, theoccurrence ofβ-1,3-glucan content peak may be proposed as a sign of the onset ofsecondary wall thickening in the cotton fiber.4. Relationship between physiological characteristics during fiber thickeningand fiber strength formation in Cotton seasonal boll(1) Difference in activity of enzymes associated with cotton fiber development andits relationship with fiber strength formationin cotton seasonal boll. By choosingfour cultivars with significant difference in fiber strength as materials, we studied therelationship between fiber strength and activity of enzymes associated with cottonfiber development in Cotton seasonal boil. The results showed that the activities ofPOD and IAA oxidase promoted with anthesis date postponing, while the activities ofsucrose synthetase andβ-1,3-glucanase declined. Development of PSB and SB wereunder suitable temperature condition (mean daily temperature during 26℃to 28.5℃)and plant physiological age (about the third-ninth fruit branch), and the fibers hadhigher activity of related enzymes which resulted in better characteristic of cellulosedeposition and higher strength fiber. The strength of EAB fiber was higher than PSBthough the plant physiology age and temperature condition of PSB were better thanEAB. The main reason might be EAB had higher activities of sucrose synthetase andβ-1,3-glucanase and longer period for cellulose deposition. In LAB, the activity peaks of POD, IAAO and sucrose synthetase delayed and growth process became slowerwith the temperature condition got worse (mean daily temperature lower than 20℃)and cotton plant was senescing (above the seventeenth fruit branch), and theseresulted in much lower strength fiber formation. Although the activities of sucrosesynthetase andβ-1,3-glucanase in LAB were higher than other seasonal bolls, it wasno good for cellulose deposition and fiber strength formation. As a conclusion, Cottonseasonal boll had differences in enzymes activity and cellulose deposition. Thesephysiological phenomena might one of important reasons for different fiber strengthformation among Cotton seasonal boll. The results were similar among genotypeswith great difference in cotton fiber strength.(2) Difference of physiological characteristic during cotton fiber thickening and itsrelationship with fiber strength formationin in Cotton seasonal boll. To investigatethe physiological characteristic of cotton fiber thickening in Cotton seasonal boll andits incidence on fiber strength, experiments were carried out by choosing fourcultivars with significant difference in fiber strength as materials. The results showedthat there were great differences in matter transformation and related enzymesactivity during cotton fiber thickening in Cotton seasonal boll, which resulted indifferent fiber strength formation. The diversity of physiological characteristic duringcotton fiber thickening among Cotton seasonal boll was similar in every cottongenotype. Under suitable temperature condition and plant physiological age, PSB andSB had more soluble sugar and sucrose transformed, higher peak ofβ-1,3-glucancontent at the onset of secondary wall thickening, higher activities of sucrosesynthetase andβ-1,3-glueanase, longer and tempered cellulose accumulation, andhigher strength fiber. EAB had worse temperature environment for fiber developmentthan PSB during the later development period, but it had more matter transformed andthe characteristic of cellulose deposition was better than PSB. As the result, its fiberstrength was higher than PSB. With the temperature falling (mean daily temperaturelower than 20℃) and cotton plant senescing, the period taking for cellulose rapiddeposition prolonged, while the matter transformation rate and cellulose accumulationspeed decreased evidently in LAB fiber. And all these resulted in retardation of fiberdevelopment and the lowest final fiber strength in Cotton seasonal boll.