Yasutaka Kano

Relationship between the occurrence of bitter fruit in cucumber (Cucumis sativus L.) and the contents of total nitrogen, amino acid nitrogen, protein and HMG-CoA reductase activity

In order to describe the mechanism of the occurrence of bitter fruit in cucumbers (Cucumis sativus L. cv. Kagafutokyuri) and encourage more profitable effects by growers, an investigation of the development of the bitter principle, cucurbitacin C, was conducted. The occurrence of bitter fruit was higher in plants grown in lower air temperatures, in plants of the bitter lines and in plants cultivated with twice as much nitrogenous fertilizers as usual, than in plants grown in higher air temperatures, in plants of the non-bitter lines and in plants cultivated with the usual amount of nitrogenous fertilizers. Total nitrogen, amino acid nitrogen, and protein contents and HMG-CoA reductase activity were higher in leaves of plants that produced higher occurrence of bitter fruit, and were higher in the bitter fruit than in the non-bitter fruit.

Effects of soil temperature on hollowness in Japanese radish (Raphanus sativus L. cv. 'Gensuke')

Abstract To examine the effect of high soil temperature on the development of hollowing in the root of radish, seeds were sown in the field on 27 May, 10 July and 16 August 1992. Plants of the July sowing were subjected to soil temperatures above 32 °C during the middle of the growth period. Root weight was reduced and hollowness occurred in roots from the July sowing. Roots of the July sowing had the greatest concentration of vessels in the central region. Lignin formed in walls surrounding the central cavity only in roots of the July sowing. In a second experiment, seeds were sown on 30 April 1991, in plastic pots with heating cables to increase soil temperature. Heating from the 16th day after sowing (DAS) to the 30th DAS and from the 31st to the 45th DAS slowed root growth, and produced some hollow cavities, caused more vessels to form in the central area, and promoted lignification near the central cavity. In contrast, heating from the 10th to the 15th DAS or from the 46th to the 60th DAS produced roots with no hollow cavities, and resulted in the production of a smaller number of vessels in the central region of the root. The heating during these periods had no effect on lignin formation. In conclusion, a large hollow cavity develops in the central region of the root as a result of active lignin formation in the surrounding cells induced by heating in the middle of the growth period.

Suppressive effects of CPPU on lignification of xylem parenchymatous cells and on hollowing in the root of Japanese radish (Raphanus sativus L.)

Abstract To see the effects of CPPU on the development of hollowing and lignin formation in the roots of Japanese radish ( Raphanus sativus L.) ‘Wakayama’, ‘Yamada’ and ‘Osakashijunichi’, solutions of 5 mg l −1 of 1-(2-chloro-4-pyridyl)-3-phenylurea (CPPU) were sprayed on the leaves of plants every 3 days from the 11th to the 40th days after sowing (DAS). The size of the hollow cavity in the roots of ‘Wakayama’, ‘Yamada’ and ‘Osakashijunichi’ became significantly smaller with CPPU treatment, in contrast to that of the control. Vessels in the roots of all cultivars became more sparsely arranged with CPPU treatment, compared with vessels in the root of the control. In addition, the central region of the root of all cultivars treated with CPPU was filled with parenchymatous cells and these cells showed little staining reaction to phloroglucinol-HCl reagent. In contrast, in the controls, there was clear evidence of the presence of lignin in parenchymatous cells facing the intercellular space.

Role of endogenous cytokinin in the development of hollowing in the root of Japanese radish (Raphanus sativus L.)

Abstract The size of the hollow cavity increased with time in plants of the early sown plot (ESP), whereas its size remained almost unchanged throughout the growth period in plants of the late sown plot (LSP). The daily maximum soil temperatures in the ESP were 6–12 °C higher than those in the LSP. A much higher level of cytokinin was detected in the ammonia eluate fraction than in the acidic ethyl acetate fraction and none was detected in the effluent and washings. Cytokinin levels in the ammonia eluate fraction and the acidic ethyl acetate fraction were low in roots from the ESP in comparison with those from the LSP. A much larger size of hollow cavity was observed at any days after sowing (DAS) in control roots, that were exposed to temperatures of 30 °C and above for 30 days, than in roots grown at lower soil temperatures between 25 °C and 30 °C throughout the growth period. Cytokinin levels in control roots grown at high soil temperature were consistently lower than those in the roots grown at low soil temperature. The production of endogenous cytokinin in the roots of cvs. Sobuto and Fukumi, cultivars that were prone to hollowness, was reduced at higher soil temperatures, while in cultivars that were resistant to hollowness cytokinin production was higher. The role of endogenous cytokinin in the development of hollowing is discussed.

Relationship between the development of hollowing and the separation of vessel sectors in the central region of the root of Japanese radish (Raphanus sativus L.)

Abstract The present investigations were carried out to clarify the relationship between the separation of two vessel sectors, especially in the later growth period, and the development of hollowing in the root and the effect of varying the cultural conditions. Roots with hollow cavities were more prevalent in plants whose seeds were sown early in the summer compared with those sown later. The gap between the bifurcated vessel sectors became larger in roots sown earlier. A larger number of hollow roots was observed in the sparsely planted plot than in the high planting density plot, and the gap between the bifurcated vessel sectors became larger in roots at low planting density. Late defoliation, after rapid thickening growth, produced a large number of hollow roots, while early defoliation prevented the root from hollowing due to slower thickening growth. The gap between the bifurcated vessel sectors became wider the later the time of defoliation. A larger number of hollow roots occurred in proportion to increasing amounts of basal fertilizer and larger amounts of basal fertilizer application resulted in a wider space between the two vessel sectors. These facts strongly indicate that the development of hollowing may pass through two indispensable steps. First is the obstruction of cell formation inside the intercellular air space during the middle of the growth period, caused by high soil temperatures. Second is the rapid divergence of bifurcated vessel sectors during the later growth period as a result of enhanced thickening growth. If the first condition is present, the second is the determining factor for the development of hollowing.