The contents of 4-methylthio-3-butenyl isothiocyanate (MTB-ITC) in roots of Japanese radish (Raphanus sativus L. ) were determined by gas chromatography to evaluate the relative pungency of cultivars. The relationship between the content of MTB-ITC and the taste of grated radish was also examined.The contents of MTB-ITC in more than half of the commercial cultivars ranged from 200 to 300μmol/100ml juice. Among the cultivars examined, ‘Karami’ showed the highest content of MTB-ITC, reaching as much as 1735μmol/100ml, followed by ‘Shinshu-jidaikon’ group of 400-700μmol/100ml. ‘Ninengo’ and ‘Shiroagari’ groups also exhibited relatively high content averaging more than 300μmol/100ml. On the contrary, ‘Miyashige’ group or Chinese cultivars contained the lowest level of MTB-ITC ranging from 100 to 200μmol/100ml.Coefficients of variance in MTB-ITC content among individual roots were 32-43% in oldtype purebred cultivars, and 12-14% in recently-released F1 hybrid. A significant negative correlation (r=-0.789) was observed between the content of MTB-ITC and the water content of the tissues among cultivars.The result of sensory evaluation on grated radish showed that a cultivar with higher content of MTB-ITC was proportionately more pungent, supporting the idea that this substance is the pungent principle in roots of Japanese radish.
The growth and quality of cut flowers of chrysanthemum (Dendranthema grandiflora cv. Syuho-no-chikara) were compared among various types of hydroponic systems during June to October. The systems were 1) capillary mat/drainage (CM/D), 2) capillary mat/recycling (CM/R), 3) deep flow technique/intermittent circulation (DFT/IC), and 4) deep flow technique / continuous circulation (DFT/CC) . The same concentration of the nutrient solution was supplied to the four hydroponic systems. Soil culture was designated as a control. The stem length and flower diameter in the CM/D and DFT/IC systems were the same as those in the control, while the stem diameter in those systems was larger than the control. In the DFT/CC systems, plants with the least height and the weakest stem were produced. The vase life of cut flowers was almost equal in the two CM systems and the control, while it was shorter in the two DFT systems. The poor growth in the DFT/CC system would not be due to the deficiency of dissolved oxygen, but to the undesirable rise of solution temperature in the summer season. These results show that a higher quality of chrysanthemum can be produced in the capillary mat system than in the DFT system.
Applicability of the integrated solarimeter film (Taisei Chemical Co. Ltd., Optleaf R-2D) for the measurement of amount of light-interception by individual leaves in fruit vegetables was investigated. The fading rate of the film was highly correlated with the values measured by an integrated solarimeter at an open field, though the rate was depended on the air temperature during the measurement. Integrated solar radiation in a glasshouse could be estimated by the film as well as at an open field. Amount of light-interception by individual leaves of vertically trained watermelon plants could be measured by the film and light-interception characteristics of the plants could be expressed numerically. The integrated solarimeter film would be useful for analyzing light-interception characteristics in fruit vegetables.
The physiological responses of pot-grown tea plants to various levels of nitrogen fertilizer were investigated to determine the suitable level of nitrogen for tea plants. Defining an arbitrary unit of nitrogen application as 1 N plot (200 mgN pot-1 year-1, corresponding to 10 kgN 10a-1 year-1), experimental plots from 0 to 27 N were prepared using ammonium sulphate. The plants exhibited symptoms of nitrogen deficiency below 3 N plots. High photosynthetic activity and favorable growth were observed from 6 to 12 N plots. Tip-burn of mature leaves and inhibition of photosynthesis were first detected at the level of 15 N plot. At the level of more than 18 N plots, the falling of mature leaves, depression of root respiration and death of some plants occurred. Based on these results, the critical level for growth and yield was determined to be 6 N plot. Nitrogen uptake increased with the increase in the amount of nitrogen applied, while the capacity of uptake gradually saturated. The recovery rate of applied nitrogen declined linearly with the increase in nitrogen dressing. The concentration of free amino acids in the first flush shoots increased in an unlimited manner with the increase in nitrogtn dressing. However, the absolute amounts in the new shoots were greatest in 9 to 15 N plots due to the inhibition of new shoot growth in heavily manured plots. Thus, with respect to the accumulation of free amino acids, the critical level for leaf quality is estimated to be around 12 N plot. The theanine content in the first flush shoots increased up to 9 N plot. Thereafter, a high content of arginine was detected, implying disorder in the nitrogen metabolism. These results demonstrate that the critical level of nitrogen for leaf quality is very close to the toxic level and is twofold greater than that for growth and yield.
SUMMARY Absorption of nitrogen dioxide (NO 2 ,) by eight herbaceous species was determined by the 15 N dilution method. The plants were continuously exposed to NO 2 , at 0.5 μll −1 for 2 weeks. Susceptibility to NO 2 , was simultaneously examined in the tested species to see if this was correlated with the rate of absorption. The total amount of NO 2 ‐nitrogen absorbed by a plant during the 2‐week exposure period primarily depended on the size of the plant. Among the tested species, sunflower showed the highest rate of NO 2 , absorption per unit leaf area, reaching as much as 0.55 mg N dm −2 d −1 , which was about four times greater than that for sorghum which had the lowest rate. A highly significant correlation was observed between the rate of absorption and the stomatal conductance among the species. A proportion of the NO 2 ‐nitrogen accumulated in the plant might be absorbed via the air‐soil‐root route. Sunflower and radish which had higher rates of NO 2 absorption than the other species were more susceptible to NO 2 . On the contrary, sorghum and maize which showed a lower rate of NO 2 , absorption were tolerant. Consequently, the higher susceptibility to NO 2 of radish and sunflower is considered to be directly related to their superior ability to absorb NO 2 .
