To investigate the effects of night temperature on sugar accumulation in watermelon fruit, fruits were treated with higher nighttime temperature under a greenhouse. The minimum nighttime ambient temperature of the heating box (18 °C) was ≈6 °C higher than that of the control. The heat-treated fruit weighed at the end of heating treatment, 16 days after anthesis (DAA), was greater than that of control, but fruit weight at harvesting, 42 DAA, was almost the same in both treatments. Cells of all portions of the heat-treated fruit at 16 DAA were much larger than those of the control, and cells in the outermost rectangular parallelepipeds (RPs; 15-mm long samples that were serially collected from a 10-mm thick disk along a 10-mm wide strip removed at the maximum transverse diameter of the fruit) of the heat-treated fruit were 80 μm or more larger than those of the control. At 16 DAA, the number of RPs with sucrose contents of 2 g·L−1 or more were six and nine in control and heat-treated fruit, respectively. At 42 DAA, content in the outer RPs of the heat-treated fruit was greater than that in the outer RPs of the control. The number of RPs with sucrose contents of 40 g·L−1 or more was five in the control and 11 in heat-treated fruit. Mean sucrose, glucose, and fructose in fruit at 16 DAA did not differ in the treated fruit from the control. However, the sucrose content of heat-treated fruit was 32% higher than that of the control at 42 DAA. Glucose and fructose content were lower in heat-treated fruit than in the control.

No abstract

No 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' F 1 hybrids. In every F 1 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.

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 H 2 O 2 detoxifying pathway derived from PPO accompanied a decline in H 2 O 2 -decomposing capacity of the ascorbate-glutathione cycle by cell destruction is one of the main reasons for the occurrence of IB.