Assimilates tuber storage

During initial development, structural growth generally has a higher priority in the hierarchical scheme of photosynthate distribution than stem and tuber storage sites. The relative importance of structural development is illustrated by the fact that after severe defoliation, the stem and leaves have the highest priority for assimilates as the plant reestablishes its carbon fixation intrastructure (Swanton and Cavers, 1989). 

The onset of tuberization entails rapid cell division and expansion, during which time the initial structural framework required for assimilate storage is established, a developmental step that occurs well before the influx of carbon during tuber bulking. While tuber initiation appears to be in part controlled by carbohydrate supply, bulking is strongly modulated by photoperiod, even in clones that are day neutral for flowering. 

Timing during the development cycle is also a critical factor. For example, during the first half of the developmental cycle, photosynthate is partitioned predominantly into stem storage sites (Incoll and Neales, 1970 McLaurin et al., 1999). However, with the onset of tuber bulking, allocation within the plant shifts dramatically. Now a major portion of new assimilate preferentially moves into the rapidly developing tubers, and assimilate previously stored in the stems begins to be recycled to the tubers. 

Jerusalem artichokes temporarily store assimilates in several locations within the plant that are in excess to the amount needed for structural and maintenance purposes. Most of these reserves are reallocated to the tubers during bulking. While a cross section of assimilates is found in these sites, carbohydrates predominate, of which inulin is the primary storage form. In addition to mono- and disaccharides and small amounts of starch, a number of nutrients are found, many of which are phloem mobile and reallocated to the tubers during the latter part of the growing season. 

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