Micropropagation of plants is a multibillion dollar industry being practiced in hundreds of small and large nurseries and biotechnology laboratories throughout the world. However, there are also many problems associated with the commercial produciton of micropropagated clone-plantlets. In commercial tissue culture laboratories, the most commonly used light sources for micropropagation are fluorescent lamps. However, the serious problem in facilities is high electric consumption for lighting and air-conditioning which make micropropagation more costly. To reduce the production cost,three low power consumption light sources: such as light emitting diodes (LED), cold cathode fluorescent lamps (CCFL), and Side Light Hollow System (SILHOS) have been recently developed. The purpose of this paper is to examine whether these light sources could be used for micropropagation. The effectiveness and usefulness of using such novel radiation systems as compared to that of conventional fluorescent system for micropropagation will be discussed.

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Low-light irradiation (LLI) during low-temperature storage maintains dry weight and preserves quality of green plants (chlorophytes) such as cuttings, plug seedlings, and postharvest culinary herbs. Under LLI, carbohydrates assimilated via photosynthesis compensate for the loss of carbohydrates to respiration during storage. Because of their advantages over other types of light source, we have exclusively employed light-emitting diodes as the light source for LLI. Here, I describe the effects of LLI during storage, discuss some of our research progress, and introduce a recently developed automatic control system for regulating photosynthetic photon flux density in order to optimally maintain dry weight of stored green plants.

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In spite of the usefulness of chlorophyll fluorescence imaging as a tool to obtain plant physiological information from intact plant without contact, the use of the chlorophyll fluorescence imaging as a plant diagnosis technique is not active in protected horticulture. In order to apply this technique to monitor plant status under practical conditions of protected horticulture, some appropriate modifications of commercially available chlorophyll fluorescence measurement instruments and/or formulation of own measurement protocols that suit for the research objectives should be done. To do them, fundamental knowledge of chlorophyll fluorescence and its measurement is indispensable. Here, we firstly explain the basics of chlorophyll fluorescence and its measurement, then introduce two examples of plant diagnosis with chlorophyll fluorescence imaging.

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Recently, cultivars reproduced by vegetative propagation are increasingly used to produce tomatoes with lateral shoots used for reproduction. To promote the development and uniformity of lateral shoots, treatments by decapitation and training on some tomato cultivars were investigated. The formation of lateral shoots after decapitation was fastest in the cherry tomato group, then in the common beef tomato group but slowest in the First beef tomato group. Treatment by decapitation enhanced the uniformity of lateral shoots among the various leaf positions, but the effect was insufficient. Horizontal training initially increased the number of lateral shoots after treatment, but finally the number became similar to that seen in vertical training. The number of harvested lateral shoots eventually depended on the number of leaf axils on the mother plant. The multiplication rate was about 65 times that of the mother plant by counting the lateral shoots generated from the main and the second stems.

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In the case of hydroponics, the anthocyanin content of red-leaf lettuce decreases, and the poor coloring of a leaf occurs in many cases. We investigated the effect of irradiation for blue light, UV-A, and UV-B at night, in order to promote growth of hydroponic red-leaf lettuce and coloring. As a result, anthocyanin content increased using blue light or UV-B irradiation. Growth was promoted by blue light, but it was inhibited by UV-B irradiation. When simultaneous irradiation of blue light and UV-B was carried out at night, the anthocyanin content increased remarkably. Since it was necessary to reduce input energy as much as possible for utilization, light intensity, and a cultivation stage, which can promote both coloring and growth, were examined. Relevant optical irradiation conditions at night are described below. 1) Irradiate with blue light (9.4 W m^-2) and UV-B (from 0.3 to 0.6 W m^-2) simultaneously for 4 hours or more. 2) The most effective cultivation stage is one to two weeks before a harvest day. We showed that supplementary lighting was effective in the hydroponics of red-leaf lettuce.

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In order to recycle a higher concentration nutrient solution (HCNS) for high soluble solids tomato production,a new recirculating capillary culture system (RCC system) was developed and certain characteristics of the system were investigated. The RCC system used the irrigation method with a drip tube and two capillary mats (CM) connected to a fertigation gutter. The tomato root zone was restricted using a root protection bag (RPB;made of a root protection sheet) inserted between the upper and lower CM. The total amount of nutrient solution supply using CM was changed only 0.45-0.70 L RPB^-1 (for 5 minutes), supplying 2-12L min^-1 water for the fertigation gutter. By dividing the mineral components of HCNS in basic nutrient solution (BNS:NO₃-N, P, K, minor elements, EC1.8 dS m^-1) in order to supply nutrients in response to the plant growth stage, and stress nutrient solution (SNS:Mg, Ca, Na) to control water stress, these nutrient solutions were irrigated to the RPB by drip tube and CM, respectively. The surplus drainage solution from RPB was recycled as SNS with EC control. Tomatoes were grown under two EC levels (2.0, 6.0 dS m^-1) in SNS in the RCC system and pot system irrigated with HCNS (EC 4.0 dS m^-1). In triple-truss cultivation using the RCC system,high Brix fruits (higher than 9%) were successfully harvested with recycling of all drainage solutions. Thereafter, the top fresh weight, dry weight, leaf area and marketable yield of EC6 in SNS were lower than that of EC2; Brix of tomato fruit from EC6 treatment was higher than that from EC2. There was no difference in plant growth,marketable yield and Brix of tomato fruits between the pot system and RCC system (EC2).

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The synchronization of plant somatic embryos is a key step in achieving the stable regeneration of plantlets. In this study, we established a method for synchronizing somatic embryos induced from asparagus, Asparagus officinalis L., and evaluated the embryos from the viewpoint of morphological transition and genetic stability during long-term passage. In induction cultures of somatic embryos,the total packed cell volume (PCV) of embryos depended on the initial PCV of embryogenic calli (EC). At 21 days after induction, the PCV of obtained embryos was maximized at 43 ml/100 ml-medium when the initial PCV of EC was 1.0×10^-2 ml/100 ml-medium. Mesh sieving of these somatic embryos yielded 60.6% embryo population which could develop to heart-shaped and torpedo-shaped embryos, meaning that the determined conditions were appropriate for inducing asparagus somatic embryos. Furthermore, it was demonstrated that the projected area and circularity of somatic embryos could be parameters for morphological estimation during passaging. For somatic embryos undergoing mesh sieving 42 days after induction, embryo synchronization was confirmed in terms of the projected area and circularity at 1.0-4.0 mm² and 1.2-1.6, respectively. From morphological assessment, it was found that prolonged passaging induced abnormal embryos. Genetic analysis was conducted using plantlets regenerated from somatic embryos harvested at 42 days and 70 days after induction by means of RAPD-PCR(random amplified polymorphic DNA-polymerase chain reaction), and it was suggested that some of the embryos suffered genetic alternations through long-term passaging.

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Attempts were made to estimate the flowering date of ‘Kawazu-zakura’ cherry trees in the Minamiizu region using regression line, DTS (the number of days transformed to standard temperature) method and the method that considers the process of rest break based on the developmental model of ‘Satonishiki’. The data used for calcula-tions in this study were 29 pairs of flowering days and temperatures over four years at eight Minamiizu stations. The error was calculated with RMSE. The calculated RMSE error of the regression line was 7.36, that of DTS method was 7.94 and that of the method considering the process of rest break was 12.22. It was difficult to assume the period of breaking endodormancy using the developmental model of ‘Satonishiki’. In the regression line method, RMSE between the observed and estimated flowering dates was about 7 days. The flowering period of ‘Kawazu-zakura’ is comparatively long,which promotes sightseeing. However, the error was large in the method. There-fore, it shall be necessary to study ways of improving the flowering forecast method.

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