In the root zone of the soil-less culture, stress conditions such as low temperature, drought and high salinity can be easily introduced and controlled by applying physical and chemical characteristics of water. These stress conditions in the root zone cause depres-sions in root absorption and leaf photosynthesis and resultantly bring osmotic stress and oxidative stress in the plant body. The osmotic stress and the oxidative stress can induce the respective plant adaptive functions of osmotic adjustment and antioxidation. These plant functions can be expected to bring high quality and value-added vegetables enriched with sugars, functional amino acids, antioxidants etc., if the induced stresses are not so serious that the stress damages are not fatal without the extreme depression in growth. In this paper, two examples of the short term stress application only to roots for production of value-added vegetables are demonstrated. By the one week application of low temperature (5°C) stress only to roots of spinach plants (Spinacia oleracea L.), sugars, ascorbic acid and Fe²⁺ were significantly enriched in leaves. Furthermore, concentrations of harmful substances of NO₃^- and oxalic acid were extremely decreased. The two weeks salt stress treatment to roots of tomato plants (Lycopersicon esculentum Mill.) by applying the Muroto deep seawater at the stage of rapid fruit growth induced the osmotic adjustment and the antioxidation, which brought high quality tomatoes enriched with sugar, minerals, functional amino acids and good flavour without occurrence of extremely small-sized fruits and blossom-end rot. These verify that the short term stress application only to roots in the soil-less culture is reliable for production of high quality and value-added vegetables.

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Storage temperature for fruits is usually maintained constant at low level. In recent years, however, there has been much interest in heat stress application that reduces the quality loss of fruit during storage. In this study, dynamic optimization of heat stress application for reducing the water loss and respiration in fruit during storage was investigated using intelligent approaches. Over a temperature range from 15 to 40°C, the control process was divided into l steps (l=6). The dynamic change in the rate of water loss as affected by temperature was first identified using neural networks, and then the optimal combination of the l-step set points for temperature that minimized the rate of water loss (or respiration) was searched for through simulation of the identified model using genetic algorithms. A double heat stress application, such as T_opt={40, 15, 40, 15, 15, 15°C}, was obtained as an optimal value under the range of 15 ≤T≤40°C. The length of one step is 24 hours. With a single heat stress application, the temperature first rises to the highest level (40°C), which is maintained over a period of 24h, and then suddenly drops to the lowest level (15°C). This operation repeats two times in the double heat stress application. In particular, the sudden drop in temperature from the highest level to the lowest level provided lower values of the rate of water loss than maintaining the temperature constantly at the lowest level throughout the control process. These results suggest that the optimal combination of high temperature (heat stress) and low temperature allows to maintaining freshness and improving the quality of fruit during storage.

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In order to achieve plant production in a closed ecological life support system (CELSS) in space, environmental control is a key technology because the environment is completely artificial. One advantage of the CELSS in space is that each module's gas composition and total pressure can be regulated at an optimal level. For example, the nitrogen contained in air is not necessary for plant growth, and low oxygen concentration may enhance net photosynthesis by reducing photorespiration. Hypobaric conditions, obtained by reducing nitrogen and oxygen concentrations, could facilitate gas control, reduce construction costs, and simplify maintenance of modules on a lunar base and in plant production systems on Mars. This review summarizes previous papers and evaluates significant effects of total pressure on growth and development of higher plants, especially crops. Previous studies showed that photosynthesis and transpiration of plants were enhanced under low total pressures because gas diffusion rates increase at low total pressures. Spinach and lettuce in vegetative stages can grow normally under 25 to 50 kPa total pressures. Seeds of rice and Arabidopsis thaliana germinated at 25 kPa total pressure. Flowering was normal in Arabidopsis under hypobaric conditions. Seed growth of soybean and Arabidopsis under low total pressures with a low O₂ partial pressure was greater than under the atmospheric pressure with the same O₂ partial pressure. This indicates that O₂ concentrations inside siliques were maintained higher by the higher diffusion rates prevailing under hypobaric conditions. The results indicate that if total and partial pressures are controlled precisely, plants can grow normally in their life cycle from germination to harvest under hypobaric conditions.

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When placed in rooms, plants refresh the indoor environment, relax people's minds, and promote comfort. In anticipation of these effects, plants are becoming more commonly placed in indoor environments such as homes and offices. These effects are known as “green amenity”, and constitute a field in this journal, Science and High Technology in Agriculture. I have been conducting researches on green amenity for over 15 years, and received a prize from the Japanese Society of Environment Control in Biology in 2000 for “Researches on green amenity”.
Green amenity includes the following four effects: thermal regulation and comfort improvement, psychological effects, alleviation and healing of visual fatigue, and air purification. We are conducting experiments and researches on each of these effects. In addition, due to the increasing attention on horticultural therapy, which is primarily used for elderly people, we are also conducting experiments and researches on the psychological effects of horticultural therapy as an applied field of green amenity. In addition, guidelines that meet the increasing demand for comfort at offices are becoming necessary.
Herein, I outline our recent researches on the psychological effects of green amenity as well as their evaluation methods, specifically with regard to the following analyses:1) attachment developing from looking after plants, 2) effects of liking and growing plants on human psychology, 3) effects of growing plants from seedlings and bulbs on the psychology of elderly people, and 4) effects of ornamental foliage plants on the psychology of office workers.

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This study was conducted to investigate the effects of fertilizer application rate on the growth and nitrate concentration in Mizuna compared with Komatsuna which is a Cruciferae and leaf vegetable with high nitrate concentration. The experiment was conducted using 6 treatments with differing fertilizer application rates. Standard treatment (S treatment) used half strength Otsuka-A solution and the 6 experimental treatments were 1/4S, 1/2S, S, 2S, 3S and 4S. The growth of Mizuna receiving 2S and 3S treatments were superior compared with that of those receiving 4S treatment. The growth of Komatsuna tended to increase with increasing fertilizer application rate. The nitrate concentration of Mizuna tended to increase with increasing fertilizer application rate on all examination days. These findings showed that the threshold for the fertilizer application to Mizuna could not be clearly determined by the nitrate concentration. However, the threshold for fertilizer application rate to Komatsuna appeared to range between 2S and 3S treatment based on the nitrate concentration. After 4S treatment, both Mizuna and Komatsuna showed the highest nitrate concentration; these were 6 times and 2 times higher than the standard nitrate concentrations in these plants 40 days after sowing. The SPAD value of Mizuna was lower than Komatsuna; however, the SPAD values of Mizuna and Komatsuna after S to 4S treatments were higher than those after 1/4S and 1/2S treatments. These findings indicate that effects of the fertilizer application rate on growth and nitrate concentration of Mizuna differed from those of Komatsuna. Moreover, the nitrate concentration of Mizuna has the potential to abruptly increase depending on the fertilizer application rate compared with that of Komatsuna. It is suggested that nitrogen fertilizer application rate to Mizuna needs much more careful attention than that to Komatsuna.

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In order to establish efficient vegetative micropropagation of Sandersonia aurantiaca Hook., the effects of plant growth regulators on morphological changes of the terminal floral apex were investigated. All explants cultured on Murashige and Skoog medium supplemented with 0μM NAA and 3.2μM TDZ, 3.2μM NAA and 1μM TDZ, 3.2μM NAA and 3.2μM CPPU, or 3.2μM NAA and 3.2μM TDZ formed multiple buds. The multiple buds consisted of minute adventitious buds, and divided multiple buds proliferated by subculturing on the same component medium. Some multiple buds had elongated shoots, and a miniature tuber was formed at the base of the shoot. These results indicated that Sandersonia aurantiaca was rapidly micropropagated by terminal floral apex culture on four media.

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The effect of day/night temperature on hypocotyl elongation in Zinnia elegance L. was investigated. Experiments were conducted under three different day/night temperature combinations (DIF) (15/25°C, 20/20°C, 25/15°C), and analysis of hypocotyl elongation was performed using an image processing technique. At 15/25°C, 20/20°C, 25/15°C, daily elongation of Zinnia on the second day was 0.29mm, 0.13mm and 0.05mm respectively, and was 0.27mm, 0.17mm and 0.09mm on the third day. It was clear that hypocotyl elongation in Zinnia decreased as the difference between day and night temperature increased, and Zinnia did not respond to DIF. Then, elongation in the light and dark periods were analyzed to determine why elongation decreased as DIF increased. It was found that elongation during the light period under-10 DIF, 0 DIF, +10 DIF was 0.07mm, 0.04mm and 0.04mm on the second day, and 0.08mm, 0.06mm, 0.07mm on the third day, and that there was no temperature effect on elongation. On the contrary, elongation during the dark period under-10 DIF, 0 DIF, +10 DIF was 0.19mm, 0.09mm, 0.01mm on the second day and 0.16mm, 0.10 mm, 0.03mm on the third day, and elongation during the dark period decreased as DIF increased. Since actual temperature during the dark period decreased as DIF increased, it can be said that temperature decrease during the dark period might be the primary factor causing decreased elongation of Zinnia during the dark period, and that the fundamental knowledge was obtained to regulate hypocotyl elongation in Zinnia by manipulating the day/night temperatures.

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