Effect Of Light Quality On Fiber Development And Pigment Accumulation In Brown Cotton

In comparison with white cotton, brown cotton has some inherent drawbacks, including lower yield and cellulose content, shorter length of fiber. This study described the effect of light qualities, which were achieved by covering brown cotton bolls with film filters in different colors (red, yellow, blue-violet and white), on pigment content and fiber quality of brown bolls and mature cotton fibers. Specifically, the effect of light quality on pigment content, fiber quality, pigment precursor and the fiber development-related enzymes activity were investigated in order to explore the formation mechanism of pigment and fiber quality. These results will provide the theoretical references to new strategy for improving yield and fiber quality of brown cotton. The major results were as follows:(1) Light quality played important role in fiber quality of brown cotton. For example, red light was capable of promoting boll development. Content of cellulose was increased by7.92%after treatment of red light. On the contrary, blue–violet light didn’t facilitate boll development. After treatment, the length of fiber and contents of pigment and cellulose were decreased to92.40%、88.89%、78.77%of originals, respectively. The dissolubility sugar and conversion rate in brown cotton fiber under white light were hightest.(2) Pigment content and luster of mature fiber were related to light quality. Light quality also could affect the color of isolated seed coats and fiber. The effective order ranked as red light>the control>yellow light>blue-violet light. It showed that pigment precursor in seed coat and fiber could be easily oxidated in air, and affected the pigment content by means of absorbing a certain wavelength of light.(3)The color of the seed coats and fiber of brown cotton had no apparent changes during the period of fiber elongation, but during the period of secondary wall thickening they changed from colorless to dark brown remarkably. Moreover, the color of seed coats changed earlier than that of fiber, suggesting that the transport of brown pigment was from the seed coats to the fiber.(4) Condensed tannins were the direct precursors of brown pigment. Light quality could affect the synthesis of the precursors. The effects of light quantity on the contents of all flavonoids, phenol and condensed tannin were analyzed by stepwise regression and path analysis. It was deduced that condensed tannins were the direct precursors of brown pigment. The effects of light quality on the content of soluble condensed tannins in seed coats and fiber were in order as follows: red light>the control>yellow light>blue-violet light. As to the insoluble condensed tannin, its content was the highest after treated by red light.(5)The activity of fiber development-related enzymes could affect the accumulation of brown cotton pigment. Relationship between activity of enzymes and content of pigment was analyzed by stepwise regression. The results indicated that high activity of β-1,3-glucanase, sucrose synthase and IAAO facilitated the accumulation of pigment. Additionally, the activity of β-1,3-glucanase and sucrose synthase in brown cotton treated by red light was the highest in four kinds of light treatments.