To explore the production methods of high value-added vegetables in plant factories, we focused on the interactive effects of a 24-h photoperiod and an NH₄-N application on the chemical components of leaf lettuce cultivated under artificial conditions. Compared with a 12-h photoperiod, the 24-h photoperiod significantly enhanced the total C content and lowered mineral contents except for Mn. Increased NH₄-N:NO₃-N ratio also resulted in significant increase of total C content and decrease of K, Ca, Mg, Na and Mn contents. Both 24-h photoperiod and NH₄-N application had similar significant effects on reduction of the nitrate content and enhancement of the total sugar, chlorogenic acid and total polyphenol contents. Furthermore, significant interaction of photoperiod and applied nitrogen form were indicated. Compared to the case where only NO₃-N was applied under a 12-h photoperiod, the nitrate content on a fresh weight basis was reduced by 1/10 to 1/100 by increasing NH₄-N:NO₃-N ratio under 24-h photoperiod. Similarly, the sugar, chlorogenic acid and polyphenol contents were increased 2.4-5.2, 3.8-13.4, and 1.4-2.0 fold, respectively, by increasing NH₄-N:NO₃-N ratio under 24-h photoperiod. Under our experimental condition, cultivation with NH₄-N:NO₃-N ratio of 25 % to 50 % under a 24-h photoperiod seemed to be the most effective for balancing reduction of growth and improvement of chemical components. These results could aid in the high value-added production of leaf lettuce in plant factory.

To establish a method for evaluating the dielectric spectra of unsaturated soils, spectra of the real permittivity of Toyoura standard sands (ε'_sand) with different volumetric water contents (θ) were determined by employing a vector network analyzer. Their results were verified based on a comparison with the theoretical values calculated using a modified dielectric mixing model. The spectra of ε'_sand above 0.23 m³ m^-3 could not be estimated owing to unreproducible soil packing. However, suitable spectra that approximately agreed with the theoretical spectra, were successfully estimated when θ was less than 0.19 m³ m^-3. Although further modifications of the foregoing approaches are required to obtain more reliable spectra of ε'_sand for Toyoura standard sands with high moisture contents, the proposed methods can aid in evaluating the spectra of unsaturated sands with low or moderate volumetric water contents.

In this study, we investigated the effects of GA₃ treatment duration and chilling treatment before sowing, and germination temperature on the germination of dried wasabi (Wasabia japonica (Miq.) Matsum.) seeds in October sowing. As the GA₃ treatment duration before sowing increased to 10 days, the germination rate improved significantly. The germination rate at 15 ℃ was higher than those at 10 ℃ and 20 ℃. However, using the seeds treated with GA₃ for 10 days followed by wet chilling treatment at 5 ℃ for 10 days, germination rates at 10 ℃ and 20 ℃ were improved, i.e., respectively, 63 % and 69 %, and have almost the same germination rate at 15 ℃. Since the germination rate of seeds treated with low temperature after GA₃ treatment was high in a wide temperature range, it may be possible to construct a systematic seeding raising system even in October when germination is unstable.

Leaf temperature (T_L) should be equilibrated with ambient temperature when experimentally assessing photosynthetic physiological responses to heat-stress in plants. Here, we report a rapid and reliable heat stress treatment using temperature-controlled water baths under illuminated conditions. In the experiment with varying chamber temperature (T_C), T_L stayed 33.0 ℃ and gross photosynthetic rate (PG) did not differ from that at 25 ℃, even at T_C of 40 ℃. Dipping aboveground organs into a water bath under non-illuminated conditions significantly decreased stomatal conductance (GS) at water temperatures (T_W) of 25, 30, and 40 ℃. However, under illuminated conditions, T_W had little effect on GS. Additionally, pre- and post- dipping PG did not change significantly at 25, 30, and 35 ℃ T_W with illumination. These results suggest that only temperature influences photosynthetic responses in plants subjected to the dipping treatment under illuminated conditions. PG and maximum quantum yield of photosystem II (Fv/Fm) decreased significantly at 40 ℃ T_W, this appears to be the threshold temperature for cucumber. Initial Rubisco activity significantly decreased as T_W rose above 40 ℃, but high temperature did not affect total Rubisco activity. We conclude that a T_L of 40 ℃ deactivates photosystem II and deteriorates Rubisco’s activation state in cucumber, thus inhibiting photosynthesis.

In this study, we developed a non-destructive technique to evaluate fruit maturity based on fluorescence measurement and investigated its utility. The purpose of this technique is to adequately control the quality of climacteric fruits that show changes in taste and texture during ripening. The fluorescence maturity index (FMI), which is defined as the logarithm of F685/F740, was used for the evaluation. Here, F685 and F740 were the chlorophyll-a fluorescence intensity at 685 and 740 nm, respectively. The fluorescence at wavelength 685 nm is strongly reabsorbed into chlorophyll-a. Therefore, F685 increases relative to F740 when the chlorophyll content of a fruit decreases during ripening. As a result, FMI increases. We excited fruits using a light wavelength of 620 nm, which is not easily absorbed by carotenoids such as lycopene, and measured the fluorescence spectra emitted from the inside of the fruit. We ripened mature-green tomatoes ‘Home-Momotaro’ and examined the relationship between FMI and chromaticity (a* value and a*/b* value in the L*a*b* color space). We clarified that FMI began to increase several days before changes in chromaticity. Moreover, after the tomatoes had come to maturity, FMI changed as well as the a*/b* value. Experimental results on kiwi fruits ‘Hayward’ revealed that the FMI changes differed greatly depending on the ripening temperature, and there were good linear correlations between FMI and fruit firmness (during the immature to edible phase) as well as between FMI and sugar/acid ratio (during the immature to fully-ripened phase). These results demonstrate that FMI is applicable to evaluate the maturity of tomatoes and the quality of kiwi fruits. It is thought that this technique can be effectively applied to judge the shipment time and edible period of fruits with constant epicarp color.