Changes in carbohydrate content and gene expression during tuberous root development of sweet potato

To understand the carbohydrate metabolism during the developmental process of tuberous roots in sweet potato (Ipomoea batatas), changes in carbohydrate content of the tuberous roots and expression of three genes, encoding granule-bound starch synthase, sporamin and β-amylase responsible for the synthesis of two major abundant components, starch and protein, were examined during different stages of tuberization. Results showed that the expression of genes, starch and sucrose content were highly correlated with the size of tuberous roots suggesting that fresh weight should be more suitable than growing-day to serve as an indicator for defining developmental stages. Increase in sucrose concentration during development might play an important role in starch accumulation; not only it functions as a substrate for starch synthesis but it can also stimulate the transcription of granule-bound starch synthase gene.