Development of Sink Capacity of the "Storage Root" in a Radish Variety with a Low Ratio of "Storage Root" to Shoot

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Controling mechanisms of sink capacity are poorly understood. Previously we suggested that sucrose synthase (SuSy), but not invertase, plays an important role for sink capacity of the radish "storage root" in a variety, Raphanus sativus L. (cv.White Cherish) [Plant Cell Physiol.(1999) 40: 369]. With this variety about 50% of the total dry weight (DW) was in the "storage root" at 21 d after sowing (DAS). We investigated the sink capacity of another radish variety, R.sativus L.(cv.Kosena) with a low ratio of "storage root" to shoot. With the latter variety only 3% of the total DW was in the "storage root" at 21 DAS. Sink activity (increase in DW of the "storage root" per unit of DW present per unit of time) of the "storage root" in Kosena as well as White Cherish was strongly related to the level and activity of SuSy but not to the activity of invertase. These results confirmed that SuSy rather than invertase may be critical for the development of the sink activity of the radish "storage root" and that the reaction products of UDP-glucose and fructose are utilized for sink growth including biosynthesis of the cell wall. In Kosena photosynthates seemed to be partitioned mainly into developing leaves and fibrous roots. Differences in partitioning of photosynthates among various sinks with these two varieties are discussed including anatomical considerations.
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