Jie GE,Shuping LUO,Deying MA,Song QIANG,Zhengpei YAO

College of Agronomy Xinjiang Agricultural University,Urumqi 830052,China

The understandingofsoluble sugar transformation and accumulation of fiberGossypiumhirsutumL.after flowering is of great significance to lower the marshmallow content and enhance fiber intensity.Duet al.[1]thought the activity of POD andIAAO wascloselyrelated to growth of cotton fiber cell,and the activity was pretty low when the cotton fiber cell grew quickly while the activity reached the peak when the cotton fiber cell stopped growing.Jiet al.[2],Jianget al.[3]thought that ABA and IAA could regulate and control the thickness of secondary cell wall,and the high ABA/IAA value during the rapid thickening process of secondary cell wall was beneficial to the thickening of secondary cell wall.However,there are few studies on the biochemical substances and its dynamic changes during the growth of cotton fiber of different species of cotton in Xinjiang.This study used Zhongmian 42 and Xinluzao 36 to analyze the dynamic changes of soluble sugar,soluble protein,peroxidase and indole-3-acetic acid oxidase in order to accumulate fundamentaldata forstudying the mechanism of cotton fiber.

Materials and Methods

Tested materials

Zhongmian 42 and Xinluzao 36 were used as the raw materials for this experiment.

Related indicators and determine methods during the cotton fiber growth

Samples of cotton boll have been collected 7,14,21,28,35 and 42 days after the above-mentioned two species underwent the flowering stage,and those samples were preserved at low temperature.Cotton fiber was taken out and conserved at-40℃.The changes of soluble sugar,soluble protein,the activity of POD and IAAO in the development of cotton fiber were determined.

The content of soluble sugar wasdetermined by dint of anthrone method[4].Standard curve was depicted first,before measuring the light absorbance at the wavelength of 620 nm.Coomassie brilliant blue G-250 was applied to determine the content of soluble protein.Besides,standard bovine serum albumin was considered as the control,and the absorbance of eachtubewasmeasuredatthe wavelength of 595 nm.POD activity determination applied the guaiacol method,and IAAO activity determination can follow He’s[6],in which the amount of IAA being destroyed by 1 mm of IAAO indicated the amount of enzyme activity.

Results and Analyses

Changes of soluble protein in the development cotton fiber of Zhongmian 42 and Xingluzao 36

There were at least two distinct protein synthesis peak periods in the cell wall protein during the fiber development,one in the initial tillering stage of fiber and the other between the 15th and 20thday of boll.The synthesized protein may be involved in the expansion of fiber and the beginning of secondary wall synthesis[7].As shown in the Fig.1,the amount of soluble protein fell drastically from the 7thto 21stday after flowering,and then the content of soluble protein in Zhongmina 42 tended to remain stable after the 21stday of flowering,while the soluble protein in Xingluzao 36 dropped quickly before stabilizing after the 28thday of flowering.The content of soluble protein in Zhongmian 42 was consistent with that in Xingluzao 36,and the soluble protein in Xingluzao 36 was generally lower than that in Zhongmian 42.

Changes of soluble sugar during the cotton fiber development of Zhongmian 42 and Xingluzao 36

As was shown in Fig.2,the soluble sugar in Zhongmian 42 and Xingluzao 36 fell after the 7th to 14th day of flowering before rising drastically to the peak at 3.1 mg/g on the 21st day of flowering,and then declined quickly to the bottom on the 35th day of flowering,after which the figure remained stable.The content of soluble sugar in Xingluzao 36 was generally lower than that in Zhongmian 42.

Changes of POD activity during the cotton fiber development of Zhongmian 42 and Xingluzao 36

According to Fig.3,the POD activity in cotton boll generally showed an upward trend after the flowering.The POD activity in Xingluzao 36 increased slowly on the 7thto 14thday of flowering,after which POD activity rose rapidly.The POD activity in Zhongmian 42 climbed slowly on the 7thto 14thday of flowering,then rose quickly,after which the number fell slightly before went up considerably after the 28thof flowering.

Changes of IAAO activity during the cotton fiber development of Zhongmian 42 and Xingluzao 36

The activity of IAAO was closely related to the length of cotton fiber cell,as the activity of cotton fiber cell was low during the rapid expansion stage,and then reached the peak when the expansion stopped,which showed negative connection to the expansion of cotton fiber cell[7].As we can see from Fig.4,the IAAO activity was low on the 7th day after flowering of Zhongmian 42 and Xingluzao 36,and then there were two peaks on the 14thday and the 28thday.The IAAO activity in Xingluzao 36 was higher than that in Zhongmian 42.The IAAO activity of both two cotton species on the 28thday after flowering dropped,and was consistent with its changes.At the initial stage,the IAAO activity was low,and then the number increased continuously until to the peak when the fiber cell stopped growing,while the IAAO activity decreased after the fiber cell stopped growing.

Conclusions

POD and IAAO are two kinds of enzyme that was closely related to the growth of cell in plants[7].POD can regulate the growth of plants,and is involved in the cohesion of many structural components of cell wall,which restrains the expansion of plant cells.POD and IAAO regulate the ending of fiber extension and the initial thickening of secondary wall.Wanget al.[8]and Guoet al.[9]believe that POD is one of the major proteins that prevent the plant cell from expanding,and the POD content was pretty low when the initial cell wall was growing,while the amount increased when the secondary cell wall enhanced[10].IAAO affected the effective content tof IAA in the cell wall,adjusting the proportion of IAA and otherendogenous hormones.GA3 stimulated the fiber to certain length,and IAA increased the content of fiber.Huet al.[11]pointed out that the activity of peroxidase in Zhongmian 12 experienced one peak when the fiber stopped extending,which restrained the extension of fiber.Shanet al.[12]believed that the Xinluzao began to differentiate few days before flowering under normal condition,before the fiber extending five to fifteen days after flowering,and the secondary wall of cotton fiber thickened 15 days after flowering until to the peach 36 days after the flowering.Zhanget al.[13]considered that IAA was closely related to the fiber differentiation by promoting the thickness of secondary wall of fiber.

This experimental result demonstrates that under the same growth environment,the soluble protein within the cottonfiber ofZhongmian 42 dropped dramatically 7 to 21 days after flowering before remaining stable 21 days after flowering.The soluble protein within the cotton fiber of Xinluzao 36 dropped quickly at a larger scale than that of Zhongmian 42 before remaining stable on the 28thday after flowering,preliminary study suggested that the fiber cell extension of Zhongmian 42 was basically finished on the 21stday after flowering,while that of Xinluzao 36 was completed on the 28thday.The soluble sugar in Zhongmian 42 and Xinluzao 36 reached the maximum on the 21stday.

POD and IAAO are closely related to each other during the cotton fiber cell differentiation stage.Through determining the physical and biological indicators of cotton fiber,the content of endogenous hormone and related enzyme activity in different types of cotton fibers were studied to explore the significance of related enzyme activity under different circumstances to provide theoretical guidance to breed new species of cotton in Xinjiang.

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