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Several studies have demonstrated that electric treatment has a positive effect, respectively, on germination, root growth and post-harvest quality. Nevertheless, there is still a lack of research on the effect of electric treatment on growth characteristics and quality of whole plants. Here, we explored the effect of electric fields on two cultivars of kale (Brassica oleracea var. acephala). Three levels of electric current (10, 50, and 100 mA) were applied to the nutrient solution of hydroponically grown plants for three weeks. Kale plants subjected to the electric fields, particularly 50 mA, had higher fresh and dry weights than the control. The absence of an electric field in a Faraday cage caused a significant decrease in shoot and root growth compared with the natural electric field (control). Electrostimulation enhanced nutrient uptake by activating root hair formation and active ion transport. Plants grown under 50 mA contained 72% more calcium, 57% more total phenolic compounds, and had a 70% greater antioxidant capacity than the control. This work provides foundational information regarding the effects of electrical stimulus on plants, which could enable the development of innovative culture technologies to improve crop yields and quality.

Crepidiastrum denticulatum (Korean common name: i-go-deul-ppae-gi) is a valuable medicinal plant used in the pharmaceutical industry and as a raw material of functional foods. In this study, we investigated the effect of light quality on C. denticulatum growth, with the goal of improving the species’ biomass and bioactive compound content when grown in plant factories with artificial lighting. Three-week-old seedlings were grown for 6 weeks in a plant factory under fluorescent lamps (control) and various sets of light-emitting diodes (LEDs): three monochromatic [red (R), green (G), and blue (B)], several dichromatic RB with different ratios of R and B [R:B = 6:4 (R6B4), 7:3 (R7B3), 8:2 (R8B2), and 9:1 (R9B1)], and several trichromatic RGB [R:G:B = 5:1:4 (R5G1B4), 6:1:3 (R6G1B3), 7:1:2 (R7G1B2), 8:1:1 (R8G1B1), and 9:1:0 (R9G1B0)]. Shoot biomass (fresh weight), leaf area, leaf shape index, and water content of the shoot were significantly higher in the RGB group than in the monochromatic and RB groups. Increasing the percentage of R light improved shoot growth in the presence of G light, as in the RGB group, and this was accompanied by a high photosynthetic rate, light absorbance rate, and electron transport rate. The contents of total phenolics and hydroxycinnamic acids per unit dry weight did not differ between plants subjected to the different light quality treatments, and the contents per shoot were thus positively associated with shoot biomass. Overall, R8G1B1 was the most effective treatment for increasing shoot biomass and the accumulation of bioactive compounds; the shoot fresh weight and total hydroxycinnamic content of R8G1B1 were significantly higher, by 50 % and 60 %, respectively, than those of the control. Thus, light quality affects the biosynthesis of bioactive compounds and the shoot biomass of C. denticulatum.

Plants typically respond to environmental stresses by inducing antioxidants as a defense mechanism. As a number of these are also phytochemicals with health-promoting qualities in the human diet, we have used mild environmental stresses to enhance the phytochemical content of lettuce, a common leafy vegetable. Five-week-old lettuce (Lactuca sativa L.) plants grown in growth chambers were exposed to mild stresses such as heat shock (40 � C for 10 min), chilling (4 � C for 1 d) or high light intensity (800 mmol m � 2 s �1 for 1 d). In response to these stresses, there was a two to threefold increase in the total phenolic content and a significant increase in the antioxidant capacity. The concentrations of two major phenolic compounds in lettuce, chicoric acid and chlorogenic acid, increased significantly in response to all the stresses. Quercetin-3-O-glucoside and luteolin-7-O-glucoside were not detected in the control plants, but showed marked accumulations following the stress treatments. The results suggest that certain phenolic compounds can be induced in lettuce by environmental stresses. Of all the stress treatments, high light produced the greatest accumulation of phenolic compounds, especially following the stress treatments during the recovery. In addition, key genes such as phenylalanine ammonia-lyase (PAL), L-galactose dehydrogenase (L-GalDH), and g-tocopherol methyltransferase (g-TMT) involved in the biosynthesis of phenolic compounds, ascorbic acid, and a-tocopherol, respectively, were rapidly activated by chilling stress while heat shock and high light did not appear to have an effect on the expression of PAL and g-TMT. However, L-GalDH was consistently activated in response to all the stresses. The results also show that these mild environmental stresses had no adverse effects on the overall growth of lettuce, suggesting that it is possible to use mild environmental stresses to successfully improve the phytochemical content and hence the health-promoting quality of lettuce with little or no adverse effect on its growth or yield. Published by Elsevier Masson SAS.

Recirculating subirrigation systems are frequently exposed to the risk of plant pathogens transmission, which may deteriorate the growth and quality of the plants. The transmission of Phytophthora nicotianae was examined using Kalanchoe blossfeldiana cv. New Alter in two recirculating subirrigation systems, a nutrient-flow wick culture (NFW) system and an ebb and flow (EBB) system. When the nutrient solution was infested, the pathogen was recovered from roots in both subirrigation systems. However, foliar blights and browning of roots appeared 4 and 7 weeks, respectively, after inoculation in the EBB system. Only a little discoloration appeared in the NFW system. The fresh and dry weights were lower in the EBB system than in the NFW system. When growing medium was inoculated, the pathogen was unable to be isolated from the plants in the NFW system. However, disease symptoms appeared in the EBB system 4 weeks after inoculation, and the pathogen was observed in the basal leaves and roots. Similar to the infested nutrient solution, the plant growth in the EBB system was inhibited. These results suggested that when the nutrient solution was infested, pathogen transmission could occur in plants in both systems, although differences existed with regard to disease symptoms and the time it took for symptoms to appear. However, we observed that when growing medium was inoculated the pathogen was not transmitted to adjacent plants in the NFW system using wick.

To compliment the current subirrigation systems used for production of potted plants, a nutrient-flow wick culture (NFW) system was developed and compared with other subirrigation systems, such as an ebb and flow culture (EBB) system and a nutrient-stagnant wick culture (NSW) system in relation to their system characteristics and plant growth. Kalanchoe ( Kalanchoe blossfeldiana cv. New Alter) was cultivated in a 6 cm pot for 10 weeks in each subirrigation system. The water-absorption pattern of the medium, water content of the medium, water loss, algal growth, salt-buildup and plant growth under various culture systems were observed. The water contents of medium under the NFW and EBB systems showed fluctuations from 30 to 40% and from 50 to 60% (by volume), respectively, whereas the water content under the NSW system gradually increased to over 40% without fluctuation. Relative to other systems, the water loss in the NFW system was 50–70% due to the reduction in the evaporation from the surfaces of the trough and medium. Algae appeared in the NSW system because the nutrient solution was always stagnant in the trough, while it was not observed under the NFW system. The dissolved oxygen in the nutrient solution was the highest during the irrigation period and the salinity in the medium was the lowest in the NFW system. With regard to system characteristics, the NFW system was simple, water-saving and efficient. In addition, the growth of kalanchoes in the NFW system was similar to those in the NSW and EBB systems at an irrigation frequency of five times a day.