Relationship between the Occurrence of Internal Browning and Size of Xylem Parenchymatous Cells in Roots of Japanese Radish

Abstract

The correlation between the occurrence of internal browning (IB) and the size of root xylem parenchymatous cells in Japanese radish (Raphanus sativus L.) was determined in 3 experiments. The first examined intervarietal differences in IB among 5 commercial cultivars (cvs.). Results revealed that the differences in susceptibility to IB largely depend on root cell size, and that mean cell length in IB-resistant cvs. was approximately 39–45% shorter than in susceptible cvs. The second experiment examined the relationship between cell size and IB occurrence in 3 IB-susceptible commercial cvs. and their ‘Gensuke’ F1 hybrids. In every F1 hybrid strain, the central region did not appear to show the propensity of its parents to develop IB, and mean cell length in the former was approximately 26–39% shorter than in the latter. The third experiment examined the effect of applying a plant growth regulator on IB occurrence and cell size. Gibberellin (GA) application during the mid-growth stage restricted IB occurrence, and the mean cell length of GA-treated plants during this period was approximately 27–47% shorter than in the control. These results strongly suggest that IB occurrence is largely dependent on the size of root xylem parenchymatous cells, and IB seldom occurs in roots with smaller cells.