Effects of sucrose and cytokinin (trans-zeatin riboside [t-ZR]) on the formation of tuberous root of sweetpotato (Ipomoea batatas (L.) Lam.) were studied by directly applying these substances to young roots. In the roots that originally contained approximately 9 μ endogenous sucrose per milligram of fresh weight (FW), further increase in the sucrose level did not necessarily result in tuberous root formation, whereas t-ZR application invariably induced tuberous root formation. However, t-ZR did not induce morphogenesis when the sucrose level in the root was lowered to approximately 2 μg mg-1 of FW. Our results imply that high levels of endogenous sucrose are necessary for tuberous root formation and that in the presence of high sucrose concentrations, cytokinins can trigger tuberous root formation. Copyrights 2008, Plant Root (JSRR).
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