Regulation of sweetpotato tuberous root forming gene with environment control.

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In sweetpotato study, researchers have not obtained cultural technique to regulate the process of tuberous root formation. Then we aimed to develop the experimental procedure for elucidation of a mechanism of tuberous root formation in sweetpotato, and to enable the artificial control of the morphogenesis by applying environment control techniques.At first, we developed the cultivation system that ensures the tuberous root formation. In the system, the root environment was divided into two layers comprised of the aerial space for the root swelling and the nutrient solution layer for uptake of water and nutrients. Single-root plants were certainly able to form the tuberous root in the aerial space. Environments of the shoot, tuberous root and fibrous root can be controlled independently in the cultivation system. Under the identical environmental condition, the formation of the tuberous root occurred earlier in initially thicker roots. After the tuberous root formation, number of leaves in the plant affected the thickening growth of the tuberous root. Secondary, we examined the effects of sugars, plant hormones and inhibition of gas exchange through root surface on the tuberous root formation. Results of this experiments suggested that elevation of the cytokinin level should be necessary for induction of tuberous root formation, and hypoxia depressed the tuberous root thickening through acceleration of lignification in the stele of the root. Furthermore, we made expression analyses of cellwall-bound invertase gene and cycline D3 gene possible in sweetpotato plants, those genes which are supposed to be related to regulation of the morphogenesis.