Research on environmental effects on the growth of plantlets in micropropagation is reviewed to give an overview on the subject conducted in the past decade, mainly to environmental biologists and engineers. Effects of aerial environmental factors including light, carbon dioxide concentration, temperature, relative humidity, oxygen and ethylene on the growth and photosynthesis of plantlets in vitro are discussed. Then, effects of culture medium environmental factors including sugar concentration, concentrations of ion components, osmotic potential and pH of the culture medium on the growth of plantlets in vitro are discussed. Lastly, effects of biological factors such as explant size and explant density on the growth of plantlets in vitro are discussed. Effects of aerial, culture medium and biological factors on the photoautotrophic (totally photosynthesis dependent) growth of plantlets are emphasized.

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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.

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Cucumber (Cucumis sativus L. cv. Naoyosi) plants were grown hydroponically at air temperatures of 28/24°C (D/N) and 300μmol m^-2 s^-1 PPF, in a walk-in type growth cabinet equipped with 3-band fluorescent lamps. For 0, 5, 30 or 120 min, blue-lighting at 30 μmol m^-2 s^-1 in PPF was applied daily just before the 14 h photoperiod (morning twilight) . Growth parameters were measured after 12 and 24 d of treatment. After 13 d of treatment, the stomatal conductance, transpiration rate and net photosynthetic rate were measured under 3-band fluorescent lamps at a PPF of 200 μmol m^-2 s^-1. At 17-19 d of treatment, changes in net photosynthetic rate affected by blue-light were measured continuously for 30 min. Fresh and dry weight, leaf area, plant height and stem diameter of plants were the greatest with bluelighting for 5 min. The stomatal conductance, transpiration rate and net photosynthetic rate after 13 d of treatment were greatest in the plants grown with supplemental blue-light for 5 min. The net photosynthetic rate for 5 min treatment increased by 60% as compared with that of control plants grown without lighting. Continuous measurements showed net photosynthetic rate to rise and the high level was maintained with 5 min blue-lighting treatment. These results indicate that the promotion of plant growth by blue-lighting during morning twilight is dependent on the lighting time. For cucumber seedlings, blue-lighting for 5 min was more effective for growth than for 30 and 120 min.

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It is known that the sink organ is not just a reservoir of carbon, but must also acquire water in appropriate proportion as the organ grows. In this study, the dynamics of tuber growth rate in sweet potato plants (Ipomoea batatas Lam.) was analyzed with reference to water relations using a newly developed system for on-line measurement of tuber volume. Tuber growth rate in the dark was higher than in the light, and the growth rate was almost parallel to the change in leaf water potential. Furthermore, transient responses of tuber growth rate were found just after rapid changes in evaporative demand, i.e. tuber growth rate drastically increased in 1 h after turning off the light, increasing humidity or excising all leaves, and the growth rate drastically decreased 1 h after turning on the light or decreasing humidity. Thus, the tuber growth rate was higher under higher leaf water potential, and it appeared to be affected by leaf transpiration through the whole plant water balance.

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Temperature and humidity environments inside an evaporative-fog air cooling greenhouse with natural ventilation were measured on a clear day in summer. The fog was sprayed intermittently (spraying time: 1 min at 3 or 4-min intervals) from nozzles installed 2 m above the floor inside the greenhouse. The side, end, and roof ventilators of the greenhouse remained open to increase air circulation and fog evaporation during cooling. The results of the experiment are summarized below. (1) The inside air temperature reduced to approximately the inside wet bulb temperature within 1 min after the start of fog spraying. (2) The vertical air temperature differences below the nozzles (plant growing zone) were within 1 °C, and the horizontal air temperature differences at 1.5 m above the floor in the greenhouse cooled with fog spray system were within 2.5°C. (3) The reduction of leaf temperature of the tomato plant by fog spray was smaller than that of air temperature. The difference between the leaf temperature and the air temperature inside the greenhouse decreased as the saturation deficit of the air increased. (4) From these measurements, when fog fills the greenhouse atmosphere, the air is rapidly cooled at a rate of 10°C per min, a small sensor, such as a small diameter thermocouple in which heat capacity is small, is recommended to prevent errors in measuring air temperature.

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A nocturnal greenhouse cooling system by a silica gel (adsorbent) -water (adsorbate) pair adsorption cooling method was proposed for an alternative cooling system by applying solar heat and waste heat from industry. According to the calculated results of the negative heat acquisition for the system, the adsorbent bed having 100 m² surface area would be able to cool a greenhouse of 340 m² floor area. The values of COP and exergy efficiency ζfor the proposed system were estimated to be 0.216 and 0.0056, respectively. Both of these are smaller than those for the absorption cooling system reported previously, because the rate of heat exchange between the adsorbent bed and medium water is limited by heat conduction and a large amount of exergy is dissipated in absorbing the solar heat. The amount of solar heat input was 3.6 times larger than that of the waste heat input in this simulation. This suggests that it is important for system stability to develop a method for concentrating the solar heat, considering the solar heat variation due to meteorological conditions.

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The influence of the rooting substrate on the root development of papaya in vitro was studied. The rooting of microcuttings started after the swelling of the basal ends. After 4 weeks of culture, the rooting rate was highest in the starch medium at 96%, followed by the agar, rockwool and vermiculite media. In the gellan gum medium, only 8% of the microcuttings rooted. Anatomically, hypertrophy of subepidermal cells and occurrence of cracking in the epidermis were observed in the starch, agar and gellan gum media. On the other hand, no structural abnormalities were detected in roots formed in the vermiculite and rockwool media. Although, the rooting rate was enhanced with increasing concentrations of agar and gellan gum, the abnormal structures still persisted in both media even when higher concentrations were applied.

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