吉田 英生

The effect of the ratio of red and blue light on fruit biomass radiation-use efficiency (FBRUE) in dwarf tomatoes has not been well studied. Additionally, whether white light offers a greater advantage in improving radiation-use efficiency (RUE) and FBRUE over red and blue light under LED light remains unknown. In this study, two dwarf tomato cultivars (‘Micro-Tom’ and ‘Rejina’) were cultivated in three red-blue light treatments (monochromatic red light, red/blue light ratio = 9, and red/blue light ratio = 3) and a white light treatment at the same photosynthetic photon flux density of 300 μmol m^–2 s^–1. The results evidently demonstrated that the red and blue light had an effect on FBRUE by affecting RUE rather than the fraction of dry mass partitioned into fruits (F_fruits). The monochromatic red light increased specific leaf area, reflectance, and transmittance of leaves but decreased the absorptance and photosynthetic rate, ultimately resulting in the lowest RUE, which induced the lowest FBRUE among all treatments. A higher proportion of blue light (up to 25%) led to a higher photosynthetic rate, resulting in a higher RUE and FBRUE in the three red-blue light treatments. Compared with red and blue light, white light increased RUE by 0.09–0.38 g mol⁻¹ and FBRUE by 0.14–0.25 g mol⁻¹. Moreover, white light improved the F_fruits in ‘Rejina’ and Brix of fruits in ‘Micro-Tom’ and both effects were cultivar-specific. In conclusion, white light may have greater potential than mixed red and blue light for enhancing the dwarf tomato FBRUE during their reproductive growth stage.

This study aimed to analyze the effects of photosynthetic photon flux density (PPFD) on fruit biomass radiation-use efficiency (FBRUE) of the dwarf tomato cultivar ‘Micro-Tom’ and to determine the suitable PPFD for enhancing the FBRUE under LED light at the reproductive growth stage. We performed four PPFD treatments under white LED light: 200, 300, 500, and 700 μmol m⁻² s⁻¹. The results demonstrated that a higher PPFD led to higher fresh and dry weights of the plants and lowered specific leaf areas. FBRUE and radiation-use efficiency (RUE) were the highest under 300 μmol m⁻² s⁻¹. FBRUE decreased by 37.7% because RUE decreased by 25% and the fraction of dry mass portioned to fruits decreased by 16.9% when PPFD increased from 300 to 700 μmol m⁻² s⁻¹. Higher PPFD (500 and 700 μmol m⁻² s⁻¹) led to lower RUE owing to lower light absorptance, photosynthetic quantum yield, and photosynthetic capacity of the leaves. High source strength and low fruit sink strength at the late reproductive growth stage led to a low fraction of dry mass portioned to fruits. In conclusion, 300 µmol m⁻² s⁻¹ PPFD is recommended for ‘Micro-Tom’ cultivation to improve the FBRUE at the reproductive growth stage.

Abstract Ophiorrhiza pumila is a medicinal plant that grows in subtropical forests and produces camptothecin (CPT). To determine an optimal harvest time of O. pumila in a plant factory with artificial light (PFAL), we investigated the CPT distribution in each organ and at the developmental stage and estimated the annual CPT production. For this study, the O. pumila plants were grown in controlled environments (16 h light period, photosynthetic photon flux density of 100 μmol m⁻² s⁻¹ under white light-emitting diode lamps, air temperature of 28 °C, relative humidity of 80%, and CO₂ concentration of 1000 μmol mol⁻¹). First, the stem, root, and seed pod had higher CPT contents than the leaves, flower, and ovary. The optimal harvest time of O. pumila in a PFAL was 63 days after transplanting (DAT), because the CPT content in the whole organs was the highest at the seed-ripening stage. Second, based on these results, the estimated annual CPT production of O. pumila cultivated in a PFAL was 380 mg m⁻² y⁻¹ (63 DAT). This value was 4.3 times greater than the annual CPT production by Camptotheca acuminata in a greenhouse. We concluded that the CPT production by O. pumila in a PFAL throughout the year has many advantages, although the demand for electrical energy was high compared to that of Camptotheca acuminata in a greenhouse.

The demand for high-quality tomatoes is increasing; however, their production requires skillful techniques. To develop an automated irrigation method for producing high-quality tomatoes in a greenhouse, we used an image-based irrigation system to study how a diurnal periodic cycle of wilting–partial recovery irrigation affects growth, yield, and fruit quality. Three irrigation treatments were performed: a control with sufficient irrigation and two water stress treatments (moderate and severe wilting–partial recovery treatments; MPR and SPR, respectively). The mean daily maximum wilting ratios for MPR and SPR were 8.1% and 13.2% at wilting-level setpoints of 7% and 14%, respectively. The total irrigation amounts in MPR and SPR were 75% and 59% of that in the control, respectively. The corresponding yields in MPR and SPR were 76% and 56% of that in the control, respectively. The Brix and acidity of fruits in MPR and SPR were 15% and 10% and 34% and 24% higher, respectively, than those in the control at the end of the experiment. Plant growth decreased with increasing water stress levels. Plant length, leaf area, and the number of leaves were more sensitive to water stress than other growth parameters. SPR could be an effective irrigation method to improve fruit quality, even at high-air-temperature periods in summer.

The leaf of red perilla is used as an herbal medicine in Japan. For efficient production of red perilla in a plant factory with artificial light, it is necessary to investigate the fundamental behaviour in bioactive compounds, such as perillaldehyde (PA) and anthocyanin (ANT). Red perilla seeds were cultivated in a controlled-environmental chamber for 30 days post-germination. On day 30, the plants were grown under various levels of photosynthetic photon flux density (PPFD: 50, 100, 200, and 400 µmol m-2 s-1), provided with white fluorescent lamps in a controlled environment. After 35 days, PA and ANT levels at each different leaf position were measured. We also measured PA and ANT concentration at the same leaf position every 3 days, at 200 µmol m-2 s-1 PPFD, to investigate the changes at different leaf ages. A gradual decrease in PA concentration from the upper leaf position to the lower leaf position at all PPFD levels was observed, while the ANT concentration was almost constant regardless of leaf position. The concentration of PA was not significantly different among various PPFD levels. ANT concentration differed significantly only between 50 and 200 µmol m-2 s-1 PPFD. PA concentration gradually decreased from 3 days to 15 days after unfolding. In contrast, the ANT concentration was almost constant regardless of leaf age. Our results suggest that harvesting upper red perilla leaves is suitable for efficient production of bioactive compounds in red perilla in a plant factory.

In this study, we developed an automatic irrigation method using an image-based irrigation system for high-quality tomato production in a greenhouse by investigating effects of a diurnal periodic cycle of irrigation on the photosynthesis, growth, yield, and fruit quality of tomatoes. The diurnal periodic cycle in a moderate wilting–full recovery treatment (MR) with a medium threshold value was more frequent than that in a severe wilting–full recovery treatment (SR) with a high threshold value. Mean daily maximum wilting ratios for MR and SR were 7.2% and 11.3%, respectively, when wilting ratios were set to threshold values of 7% and 14%, respectively. Total irrigation amounts in MR and SR were similar and lower than that in the untreated control. Net photosynthetic rate decreased under water stress, with values in MR being higher than that in SR, and recovered rapidly to more than 90% of its maximum value following irrigation. Plant growth and fruit yield per plant in MR and SR were lower than that in the control. Water stress treatment could improve fruit quality when it commenced at the anthesis stage or early fruit development stage. Total irrigation amount was a more important parameter than the threshold value for controlling the growth, yield, and fruit quality of tomatoes.

Dwarf tomatoes are advantageous when cultivated in a plant factory with artificial light because they can grow well in a small volume. However, few studies have been reported on cultivation in a controlled environment for improving productivity. We performed two experiments to investigate the effects of photosynthetic photon flux density (PPFD; 300, 500, and 700 μmol m-2 s-1) with white light and light quality (white, R3B1 (red:blue = 3:1), and R9B1) with a PPFD of 300 μmol m-2 s-1 on plant growth and radiation-use efficiency (RUE) of a dwarf tomato cultivar ('Micro-Tom') at the vegetative growth stage. The results clearly demonstrated that higher PPFD leads to higher dry mass and lower specific leaf area, but it does not affect the stem length. Furthermore, high PPFD increased the photosynthetic rate (Pn) of individual leaves but decreased RUE. A higher blue light proportion inhibited dry mass production with the same intercepted light because the leaves under high blue light proportion had low Pn and photosynthetic light-use efficiency. In conclusion, 300 μmol m-2 s-1 PPFD and R9B1 are the recommended proper PPFD and light quality, respectively, for 'Micro-Tom' cultivation at the vegetative growth stage to increase the RUE.

In Japan, red perilla leaves are used in the food and coloring industries, as well as in crude medicine. Perilla leaves contain a high concentration of phytochemicals such as perillaldehyde (PA) and rosmarinic acid (RA). The effects of UV-B radiation intensity (0.05–0.2 W m−2, UV-BBE: 0.041–0.083 W m−2), duration (3 or 6 h), and irradiation method (continuous or intermittent) for artificial nocturnal lighting using UV-B fluorescent lamps were evaluated on growth, flowering, and leaf phytochemical concentration in greenhouse-grown perilla. Under continuous UV-B irradiation at 0.1 W m−2 for 3 or 6 h, leaf color changed from red to green and leaf fresh weight decreased, compared with the control treatment. No leaf color change was observed under the 3-h treatment with UV-B radiation at 0.05 W m−2, wherein leaf fresh weight was similar to that of the control. Furthermore, RA concentration under continuous UV-B irradiation at 0.05 W m−2 for 3 h increased two-fold compared to that under control treatment, while PA concentration was not affected by UV-B irradiation. Thus, our data showed that continuous UV-B irradiation at 0.05 W m−2 for 3 h could effectively produce RA-rich perilla leaves without reducing in phenotypic quality or productivity. However, a 6-h intermittent illumination inhibited flowering without altering phytochemical concentration.

We studied the effects of varying light quality on the flowering, photosynthetic rate and fruit yield of everbearing strawberry plants (Fragaria×ananassa Duch. ‘HS138’), which are long-day plants, to increase the efficiency of fruit production in plant factories. The plants were grown under continuous lighting using three types of blue and red LEDs (blue light peak wavelength: 405, 450, and 470 nm; red light peak wavelength: 630, 660, and 685 nm) during the nursery period. All blue light from the various peak LED types promoted more flowering compared with red light (630 and 660 nm except for 685 nm). The longer wavelength among the red light range positively correlated with earlier flowering, whereas the number of days to anthesis did not significantly differ among blue LED treatment wavelengths, irrespective of peak wavelength. The result of a similar experiment using the perpetual flowering Fragaria vesca accession Hawaii-4 representing a model strawberry species showed almost the same pattern of flowering response to light quality. These results suggest that long-day strawberry plants show similar flowering response to light quality. The photosynthetic rate under red light (660 nm) was higher than that under blue light (450 nm). However, the plants grown under red light showed lower photosynthetic capacity than those grown under blue light. Although the light color used to grow the seedlings showed no difference in the daily fruit production, blue light irradiation during the nursery period hastened harvesting because of the advance in flowering.

In Arabidopsis, flowering is delayed under red light and induced under far red light and blue light. Studies suggest that the florigen, FLOWERING LOCUS T, is involved in the control of light quality-associated flowering in Arabidopsis. In petunia, similar to Arabidopsis, flowering is delayed under red light and induced under blue light, however its mechanism still remains unknown. Here we isolated a gene which has 75% amino acid sequence similarity with Arabidopsis FT (AtFT), named PehFT. By overexpressing PehFT in Arbidopsis and petunia, we tested its ability to induce flowering. Also, by conducting expression analyses of PehFT under different light quality treatments, we tested its response to light quality. We concluded that PehFT, like AtFT, is a gene which responds to photoperiod and light quality, but unlike AtFT, is not the main gene controlling the light quality-associated flowering.

The transgenic everbearing strawberry (Fragaria×ananassa Duch. ‘HS 138’) can be cultivated in a closed plant production system to produce functional proteins that enhance human immune functions. In this study, we investigated the effects of light quality on fruit growth and the concentration of human adiponectin (hAdi) at three mature stages in transgenic strawberry. hAdi plants were exposed to 3 different light qualities (white [W], blue [B], and red [R]) for a 16-h light period under fluorescent lamps during the flowering and harvest stage; fruits were then harvested at three different mature stages (small green, turning white, and mature red). hAdi concentration increased with fruit maturation, and the mature red stage fruit from the R light treatment group had a significantly greater concentration of hAdi on a fresh-weight basis than all other treatments. There was no relationship between hAdi concentration and fruit fresh weight and the number of days from anthesis to harvest. Although the factors that promoted the production of the functional hAdi proteins were not clear in this study, the results suggest that the fruit growth stages of the transgenic strawberry differed in their response to light quality. For hAdi plants, exposure to red light resulted in the greatest level of functional protein production under the tested treatments.

本試験では, 人工光型植物工場を用いたイチゴの栽培における初期コストの削減および栽培期間の短縮(ランニングコストの削減)を目的として, 連続明期およびその開始時期が四季成り性イチゴ苗(Fragaria×ananassa Duch. 'HS138')の花成および生育に及ぼす影響について調査した. 処理光源には, 花成促進効果が報告されている青色光を多く含む青色蛍光灯を用い, 日積算光量(Daily light integral; DLI)を13 mol m^-2 d^-1とした. 組織培養苗を水耕装置に移植後21日目から16時間明期または連続明期下で栽培したB16区とB24区, 加えて, 連続明期処理の開始を16日早め, 移植後5日目から行ったEB24区を設けた. 処理区を通じて全ての株が開花した時点で試験を終了した(連続明期処理の開始後71日目). その結果, B24区およびEB24区ともに, B16区の開花日より約20日早く開花した. 移植後21日目から処理を開始したB24区の葉面積は約50 cm², 移植後5日目から連続明期処理を開始したEB24区の連続明期処理の開始時の葉面積は約10 cm²だった. 連続明期処理の開始時期を16日早めたEB24区で花成が促進されなかったのは, 花芽分化するにはある程度の成長量(葉面積)や葉齢を確保し, 幼若相を脱する必要があるためと考えられた. 試験終了時における総乾物重にB16区およびB24区で差はなく, 連続明期下においても生理障害なく, 連続明期は16時間明期と同等の成長量を得られることが明らかとなった. 同じDLIの場合, 連続明期は16時間明期に比べ照明器具の設備コストを2/3にすることが可能である. これらのことから, 四季成り性イチゴの育苗期における連続明期下での栽培は, 16時間明期での栽培に比べ, ランニングコストの削減だけでなく, 初期コストの削減も可能であることが示された.