Light-emitting diodes (LEDs) have proven to be popular as a light source for growing plants because of their longevity and good usability. A characteristic feature of LEDs is their use of a single colored chip that can be digitally controlled in large numbers. This functional advantage of LEDs is useful in controlling the wavelength and intensity of light to suit the growth conditions of plants. Many experimental trials have used LEDs for improving the growth, quality, and storage of plants, as well as controlling their flowering. Published data indicate that some plants are highly responsive to the colour and quantity of LED light. Therefore, we constructed an LED unit with control modules that make it possible to schedule variations in light quality and quantity to maximize plant growth. We provide an outline of the components and structure of the system and describe its potential uses. The ultimate objective of this work is to develop individual schedules for the light source that are suitable for growing different vegetables. The results of growth experiments using the system indicate the potential of the digital control of LED light in improving plant productivity.

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Light irradiation is an important environment factor affecting growth and metabolism in plant cell, tissue and organ cultures. The basic characteristics of the light source, physiological and metabolic effects of irradiation are reviewed with reference to its impact on the large-scale production of plants including production of useful secondary metabolites and production of clonal plants through micropropagation.

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Comparison of the effects of supplemental lighting with fluorescent lamps inside the plant canopy on the yield of tomato plants (Solanum lycopersicum L.) was attempted under the following lighting schedules; A) 2 hours around sunrise, B) 2 hours before noon, C) 9 or 10 hours during the daytime, D) 2 hours before noon but only when sunlight was below 200 μmol m^-2 s^-1, and E) 9 or 10 hours during the daytime but only when sunlight was below 200 μmol m^-2 s^-1. Supplemental lighting increased yield in all schedules. Schedule C showed the largest increase, followed by B, and A. The limited lighting treatments (schedules D and E) were less effective than the corresponding unlimited treatments (schedules B and C). Schedule C was best in terms of increased yield in this experiment but was not efficient in terms of lighting cost. Schedule B was the most cost-effective option in this experiment but needed more decreasing of lighting costs for practical use.

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This study clarified UV-B stress, ozone stress and water stress using laser-induced fluorescence (LIF) spectra (325 nm and 375 nm) of the leaves of the peanut (Arachis hypogaea L.). The LIF spectral variation characteristics differed between the two wavelengths. At 375 nm, the fluorescence peak ratio of 685 nm to 530 nm (F685/F530) decreased in response to increased UV-B stress, corroborating the findings of our previous study using an Ar⁺ laser (351-364 nm). On the other hand, excitation at 325 nm resulted in a decrease in the F685/F530 under irradiation at 27 kJm^-2 of UV-B, with a gradual increase observed under UV-B irradiation greater than 54 kJm^-2. This increase in the F685/F530 at 325 nm was not observed under ozone and water stress. The transverse distribution of fluorescence in leaves was examined to clarify increments in the F685/F530 under irradiation at 325 nm. The findings suggested that excess UV-B irradiation damaged UV-B-absorbing pigments in the upper epidermis, and also that irradiation at 325 nm was capable of exciting chlorophyll in the palisade tissues. These results show that the use of LIF spectra with different excitation wavelengths in the UV region is effective for accurate diagnoses of stress in plant leaves.

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Since anthocyanin accumulation would become insufficient if protected culture of the red leaf lettuce is carried out, the method for improving the quality of lettuce is required. Our previous study showed that the combined irradiation of blue light and UV-B at night resulted in notable promotion of anthocyanin synthesis. In this research, we investigated whether the blue light intensity of a light period would influence anthocyanin accumulation. When the blue light intensity of the light period was increased, anthocyanin accumulation was promoted, but it was restricted to a temporary effect. To the next, we investigated the anthocyanin accumulation of the red leaf lettuce under low photosynthesis photon flux density condition using red and blue LED. As a result, anthocyanin content was the highest in 100 μmol m^-2 s^-1 blue light or simultaneous irradiation with 20 μmol m^-2 s^-1 red and 80 μmol m^-2 s^-1 blue light. The second was simultaneous irradiation with 50 μmol m^-2 s^-1 red and 50 μmol m^-2 s^-1 blue light, the 3rd was simultaneous irradiation with 80 μmol m^-2 s^-1 red and 20 μmol m^-2 s^-1 blue light, and 100 μmol m^-2 s^-1 red light was the lowest. To clarify the molecular regulation of the anthocyanin biosynthesis by light quality, we isolated five anthocyanin biosynthetic genes, CHS, F3H, DFR, ANS and UFGT from the red-leaf lettuce. Gene expression analysis from treatment to 48 hours was conducted by the real-time PCR method. The expression of the genes which involve in anthocyanin biosynthesis were not able to be observed in 100 μmol m^-2 s^-1 red light. On the other hand, in the case of 100 μmol m^-2 s^-1 blue light and simultaneous irradiation with 50 μmol m^-2 s^-1 red and 50 μmol m^-2 s^-1 blue light, up to 24 hours after the light quality treatments, the enhanced expression of CHS, F3H, DFR, ANS, and UFGT were observed. Moreover, although the expression of F3H, DFR, and ANS were high level in simultaneous irradiation with 80 μmol m^-2 s^-1 red and 20 μmol m^-2 s^-1 blue light, the expression of CHS and UFGT was not so high. Therefore, it became clear to the biosynthetic mechanism of anthocyanin of red leaf lettuce that the ratio of red light and blue light is closely related.

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Rice varieties have been genetically modified to produce pharmaceutical proteins in seeds. Such production requires pharmaceutical proteins to be expressed in high concentrations and to remain stable. This can be achieved by controlling the growth environment by using a closed plant production system. In order to produce large amounts of pharmaceutical proteins, one must determine the environmental condition required to increase the growth of plants or the concentration of pharmaceutical proteins in seeds. The present study focused on determining the conditions for optimizing the growth of plants. Rice is a short-day plant. When the light period is constantly controlled such that it becomes longer than the critical day length, flower formation is delayed and growth period is prolonged, with no effect on the promotion of photosynthesis. Therefore, if the light period is regulated to exceed the critical day length only after the heading stage, enhanced photosynthesis would be achieved without the inhibition of flowering. The present study investigated the effect of light period on the growth and development of rice after heading. Rice plants at 65 d after germination -just after heading- were grown in growth chambers for 46 d under 3 different light periods (12, 16, and 20 h d^-1) under controlled environments. The number of tillers observed when the plants were grown under 16 and 20 h light d^-1 was greater than that observed when the plants were grown under 12 h light d^-1, but the highest number of ears were observed when the plants were grown under 12 h light d^-1. The shoot dry weight of plants grown under 12 and 16 h light d^-1 was greater than that of plants grown under 20 h light d^-1. The ratio of seed dry weight to shoot dry weight and the number of ripe seeds also increased when the plants were grown under a shorter light period. These findings suggested that when the light period became increasingly longer than the critical day length, the rice plants showed a tendency to promote vegetative growth over reproductive growth even after the heading stage. In conclusion, after the heading stage, a light period shorter than the critical day length is suitable for the growth and development of rice.

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