Establishment Of Ovule Culture System Of Xinluzao-19 Upland Cotton And The Influence Of Short Episode Low Temperature Treatment On Fiber Elongation And Expression Of Fiber Elongation Genes

In vitro culture of cotton ovule has been widely used in studying of cotton fiber development, which makes the research of fiber differentiation and development possible under controllable condition. There are similarities between the fibers cultured in vitro and cultured in field in their development and components. It is convenient to study the effects of various factors on initial differentiation, elongation, secondary wall synthesis of cotton fibers and to study the formation of fiber quality by using in vitro system.Since Xinjiang have not established cotton fiber culture system in vitro, the cotton fiber culture system in vitro of Xinluzao-19 was established based on the method developed by Beasley and Ting (1973). During the culture, the elongated fiber length was measured. The results showed that the fibers were elongated faster and the absolute elongated lengths were longer during primary stages (0-10d) of fiber development. At the 20th day, the elongated fiber almost reached the final-length. However, the strength of the fiber developed in 10 d was very low, which affected the accuracy of the length measurement. For the first time, the area formatted by the outline of cultured ovule and fibers was determined using digital image analysis software. This method is relative easier than length measurement. The outline area of cultured ovule and fibers increased faster in early 10 d, and then slow down after 15 d. The area reached the maximum at the 20th day. The area increasing trend was similar to the length increasing trend. Since Xinjiang has the problem that early frost and lower temperature in autumn seriously affects the quality of cotton fiber. The influence of short episode low temperature treatment on fiber elongation and expression of fiber elongation genes was studied.The results of low temperature treatment (15℃) to cultured ovule of Xinluzao-19 showed that the primary development stage of cotton fiber (at the sixth day) was susceptible to the episode low temperature treatment (48h). But this treatment had less effect on the final length of cotton fiber, suggesting that elongation of cotton fiber has strong adaptable ability under low temperature treatment. At middle and later stage of the cultured fiber, the short episode low temperature treatment had less effect on fiber elongation and final length of the fiber. The occupied area of cultured ovule and fibers affected by low temperature had similar trend to the length of the fiber.The elongation gene expression of developing cotton fiber cultured in field and in vitro was detected by using relative quantitative RT-PCR. The expression of expansin (EXP ) and Xyloglucan endotransglycosylase (XET) was in correspondence to the fiber-fast-elongation. The relative quantitative expression of these two genes had similar kinetic trend in developing fibers cultured both in field and in vitro. During fiber elongation, the relative quantitative expression of EXP was gradually decreased and the relative quantitative expression of XET was gradually increased. The higher expression time of these genes appeared later in vitro than in field. Our results indicated that these two genes had compensating contribution to fiber elongation.After low temperature treatment to cultured ovule of Xinluzao-19 at 15℃for 48h at the sixth day of culture, the relative quantitative expression of EXP was decreased. Even after the temperature recovered for 2d, the relative quantitative expression of EXP was lower 33% than control, but the relative quantitative expression of XET was higher 149% than control, showed the adaptation. However, the low temperature treatment at the tenth day and the fifteenth day had no obvious effect on its expression rate. In summary, the short episode of low temperature treatment decreased the relative quantitative expression of EXP. Even recover the temperature, the recover of EXP expression rate and the fiber elongation rate postponed.