Abstract: Several physiological changes during the development of radish fleshy taproot were studied using the advanced inbred lines of different ratio of root to shoot（R/S）. The results showed that sink activity patterns of taproot were much similar among the four lines. The contents of carbohydrates including soluble total sugar, sucrose and fructose decreased at the beginning of taproot enlarging, and to the minimum at the stage of the primary cortex split. The sucrose content of the low R/S line NAU-LR-04 was higher than those of three high R/S lines at all stages, while the fructose content was lower in NAU-LR-04. Changes of activities of sucrose synthase (SuSy) were similar to sink activities in all lines, and the activity of SuSy in low R/S line was higher than those of high R/S lines. It can be inferred that the SuSy may play an important role in the sucrose level regulation and sink activity control during radish fleshy taproot thickening.

Key words: Radish, Fleshy taproot, Sugar content, Sucrose synthase