Abstract
The present study investigated the anatomical and chemical factors causing the internal browning (IB) in Ipomoea tuberous roots cv. Kokei No. 14. The experimental results demonstrated that roots exhibiting IB were more prevalent during the maturation period and an increase in the severity of IB symptoms was accompanied by a parallel increase in tuberous root weight. Heating treatment during maturation period inhibited optimal root growth during this period, reducing IB occurrence. Destroyed parenchyma cells were often observed in tuberous roots with severe browning compared with those in normal roots. A pronounced increase in polyphenol oxidase (PPO) and decrease of glutathione reductase (GSHR) was detected in the former cells as compared with the latter. These observations suggest that activation of the H2O2 detoxifying pathway derived from PPO accompanied a decline in H2O2-decomposing capacity of the ascorbate-glutathione cycle by cell destruction is one of the main reasons for the occurrence of IB.
