Giedrė Samuolienė

LED lighting and seasonality effects antioxidant properties of baby leaf lettuce

We report on the application of supplementary light-emitting diode (LED) lighting within a greenhouse for cultivation of red, green and light green leaf baby lettuces (Lactuca sativa L.) grown under natural illumination and high-pressure sodium (HPS) lamps (16-h; PPFD-170 μmol m(-2)s(-1)) during different growing season. Supplementary lighting from blue 455/470 nm and green 505/530 nm LEDs was applied (16-h; PPFD-30 μmol m(-2)s(-1)). Our results showed that to achieve solely a positive effect is complicated, because metabolism of antioxidant properties in lettuce depended on multicomponent exposure of variety, light quality or seasonality. The general trend of a greater positive effect of supplemental LED components on the vitamin C and tocopherol contents was in order: 535>505>455>470 nm; on the total phenol content: 505>535=470>455 nm; on the DPPH free-radical scavenging capacity: 535=470>505>455 nm; on the total anthocyanins: 505>455>470>535 nm. Further investigations are needed for understanding the mechanism and interaction between antioxidants and light signal transduction pathways.

LED irradiance level affects growth and nutritional quality of Brassica microgreens

This study examines the effect of irradiance level produced by solid-state light-emitting diodes (LEDs) on the growth, nutritional quality and antioxidant properties of Brassicaceae family microgreens. Kohlrabi (Brassica oleracea var. gongylodes, ‘Delicacy Purple’) mustard (Brassica juncea L., ‘Red Lion’), red pak choi (Brassica rapa var. chinensis, ‘Rubi F1’) and tatsoi (Brassica rapa var. rosularis) were grown using peat substrate in controlled-environment chambers until harvest time (10 days, 21/17°C, 16 h). A system of five lighting modules with 455, 638, 665 and 731 nm LEDs at a total photosynthetic photon flux densities (PPFD) of 545, 440, 330, 220 and 110 µmol m−2s−1 respectively were used. Insufficient levels of photosynthetically active photon flux (110 µmol m−2 s−1) suppressed normal growth and diminished the nutritional value of the Brassica microgreens studied. In general, the most suitable conditions for growth and nutritional quality of the microgreens was 330–440 µmol m−2 s−1 irradiation, which resulted in a larger leaf surface area, lower content of nitrates and higher total anthocyanins, total phenols and 2,2-diphenyl-1-picrylhydrazyl (DPPH) free-radical scavenging capacity. High light levels (545 µmol m−2 s−1), which was expected to induce mild photostress, had no significant positive impact for most of investigated parameters.

The effects of different UV‐B radiation intensities on morphological and biochemical characteristics in Ocimum basilicum L.

BACKGROUND The effects of short-term ultraviolet B (UV-B) irradiation on sweet basil (Ocimum basilicum L. cv. Cinnamon) plants at the 3-4 leaf pair and flowering stages were examined in controlled environment growth chambers. Plants were exposed to 0 (reference), 2 and 4 kJ UV-B m(-2) day(-1) over 7 days. RESULTS Exposure of basil plants to supplementary UV-B light resulted in increased assimilating leaf area, fresh biomass and dry biomass. Stimulation of physiological functions in young basil plants under either applied UV-B dose resulted in increased total chlorophyll content but no marked variation in carotenoid content. At the flowering stage the chlorophyll and carotenoid contents of basil were affected by supplementary UV-B radiation, decreasing with enhanced UV-B exposure. Both total antioxidant activity (2,2-diphenyl-1-picrylhydrazyl free radical assay) and total phenolic compound content were increased by UV-B light supplementation. Young and mature basil plants differed in their ascorbic acid content, which was dependent on UV-B dose and plant age. UV-B radiation resulted in decreased nitrate content in young basil plants (3-4 leaf pair stage). CONCLUSION These results indicate that the application of short-exposure UV-B radiation beneficially influenced both growth parameters and biochemical constituents in young and mature basil plants.

The impact of LED illumination on antioxidant properties of sprouted seeds

The objective of this study was to evaluate the effect of the light emitting diode (LED) spectra on the antioxidant properties of sprouted wheat (Triticum aestivum L.), radish (Raphanus sativus L.), and lentil (Lens esculenta Moenh.) seeds. Lighting experiments were performed under controlled conditions (PPFD - 100 μmol m−2 s−1; 12 h photoperiod; 27°C). The LED conditions used were: L1 - 638 nm; L2 - 455 nm, 638 nm, 669 nm, 731 nm (basal components); L3 - basal + 385 nm; L4 - basal + 510 nm and L5 - basal + 595 nm. Wheat and lentil sprouts were shown to accumulate less phenolic compounds and were more sensitive to light spectral differences when compared to radish sprouts. The antioxidant properties and contents of antioxidant compounds in seeds germinated in the dark were significantly lower than LED treated seeds. The higher content of total phenols and significant increase in alpha-tocopherol and vitamin C concentration resulted in altered DPPH free-radical scavenging capacity. Therefore we conclude that the LED spectra, based on basal components supplemented with green (510 nm) light can improve the antioxidant properties of sprouted seeds of lentil and wheat. The highest antioxidant properties of radish seeds were caused by radiation with supplemental amber (595 nm) light.

The impact of red and blue light-emitting diode illumination on radish physiological indices

The objective was to evaluate the effect of different combinations of red (638 nm) and blue (455 nm) light produced by solid-state light-emitting diodes (LEDs) on physiological indices (net assimilation rate, hypocotyl-to-leaf ratio, leaf area, leaf dry weight, hypocotyl length and diameter, plant length, developed leaves), variation of photosynthetic pigments and non-structural carbohydrates in radish (Raphanus sativus L., var. ‘Faraon’). Lighting experiments were performed under controlled conditions (total PPFD - 200 μmol m−2 s−1; 16 h photoperiod; 14/18°C night/day temperature). The LED conditions: 638 nm; 638 + 5% 455 nm; 638 + 10% 455 nm; 638 + 10% 455 + 731 nm; 638 + 10% 455 + 731 + 669 nm. Our results showed that radishes grown under red (638 nm) alone were elongated, and the formation of hypocotyl was weak. The net assimilation rate, hypocotyl-to-leaf ratio, and leaf dry weight also were low due to the low accumulation of photosynthetic pigments and non-structural carbohydrates in leaves. The supplemented blue (455 nm) light was necessary for the non-structural carbohydrates distribution between radish storage organs and leaves which resulted in hypocotyl thickening. Red alone (638 nm) or in combination with far-red (731 nm), or red669 for radish generative development was required.

The effects of LED illumination spectra and intensity on carotenoid content in Brassicaceae microgreens

The objective of this study was to evaluate the effects of irradiance levels and spectra produced by solid-state light-emitting diodes (LEDs) on carotenoid content and composition changes in Brassicaceae microgreens. A system of five high-power, solid-state lighting modules with standard 447-, 638-, 665-, and 731-nm LEDs was used in the experiments. Two experiments were performed: (1) evaluation of LED irradiance levels of 545, 440, 330, 220, and 110 μmol m(-2) s(-1) photosynthetically active flux density (PPFD) and (2) evaluation of the effects of 520-, 595-, and 622-nm LEDs supplemental to the standard set of LEDs. Concentrations of various carotenoids in red pak choi and tatsoi were higher under illumination of 330-440 μmol m(-2) s(-1) and at 110-220 μmol m(-2) s(-1) in mustard. All supplemental wavelengths increased total carotenoid content in mustard but decreased it in red pak choi. Carotenoid content increased in tatsoi under supplemental yellow light.

Blue light dosage affects carotenoids and tocopherols in microgreens

Mustard, beet and parsley were grown to harvest time under selected LEDs: 638+660+731+0% 445nm; 638+660+731+8% 445nm; 638+660+731+16% 445nm; 638+660+731+25% 445nm; 638+660+731+33% 445nm. From 1.2 to 4.3 times higher concentrations of chlorophylls a and b, carotenoids, α- and β-carotenes, lutein, violaxanthin and zeaxanthin was found under blue 33% treatment in comparison to lower blue light dosages. Meanwhile, the accumulation of metabolites, which were not directly connected with light reactions, such as tocopherols, was more influenced by lower (16%) blue light dosage, increasing about 1.3 times. Thus, microgreen enrichment of carotenoid and xanthophyll pigments may be achieved using higher (16-33%) blue light intensities. Changes in metabolite quantities were not the result of changes of other carotenoid concentration, but were more influenced by light treatment and depended on the species. Significant quantitative changes in response to blue light percentage were obtained for both directly and not directly light-dependent metabolite groups.

Interaction Between Flowering Initiation and Photosynthesis

The vast majority of the biological processes are dependent on solar radiation. Photosynthesis is the main process which intermediate between light and plant development. Plants utilize solar radiation as a source of energy for photosynthesis, drives water and nutrient transport (Ballare and Casal, 2000). Besides they use it as environmental cue to modulate a wide range of physiological responses from germination to fruiting (Suetsugu and Wada, 2003), modulates several metabolic pathways affecting cell metabolism, also is the basis to plant structure and molecule production, thus part of what is produced by photosynthesis is used in photomorphogenesis (Quail, 2007). That composes a complex development program called photomorphogenesis. From many developmental processes that define plant form and function, flowering is of exceptional interest. A lot of horticulturally important plants are depended upon flowering. Much effort is being put into regulating the timing of flowering. Depending on particular species sensitivity to photoperiod, the transition of apex to the reproductive stage is affected by the duration of light (Leavy and Dean, 1998; Nocker, 2001). Many flowering-time studies are based on Arabidopsis thaliana model because classic events, the daylenght sensing mechanisms can be light mediated (Bernier et al., 1993). Over the years physiological studies have led to four separate but herewith interdependent models for the control of flowering: photoperiodic induction, non-photoperiodic (autonomous/vernalization), induction by gibberellins and by carbohydrates. The floral transition in biennial photoperiod-sensitive and cold-required plants is associated with an increased content of carbohydrates in apical meristems (Blazquez, Weigel 2000). According to Corbesier et al. (1998), the concentration of sucrose increases dramatically in phloem exudates upon photoinduction in both short and long day plants, even when the photoinductive treatment and accumulation of nonstructural carbohydrates limits photosynthesis by feedback regulation (Araya et al., 2006; Araya et al., 2010; Paul and Driscoll, 1997; Paul and Foyer, 2001;). Moreover, sucrose may function as long-distance signalling molecule during floral induction (Bernier et al., 1993; Leavy and Dean, 1998). Meanwhile, accumulation of glucose has been shown to suppress expression of photosynthetic genes and induce leaf senescence, via the signalling hexokinase pathway (Dai et al., 1999). Araya et al. (2006) states, that repression of photosynthesis occurs mainly in leaves that accumulates starch. Though starch per se is not metabolically active,

THE EFFECT OF UV-A SUPPLEMENTAL LIGHTING ON ANTIOXIDANT PROPERTIES OF OCIMUM BASILICUM L. MICROGREENS IN GREENHOUSE

The effects of supplemental UV-A LED lighting on growth and antioxidant properties of two varieties of basil ( Ocimum basilicum L.) microgreens were determined. Purple-leaf ‘Dark Opal’ and green-leaf ‘Sweet Genovese’ basils were grown in greenhouse (14 days, 22/18 ± 2 °C day/night temperature, 40 ± 5 % a relative air humidity) during winter season. The main lighting system (HPS lamps and natural daylight) was supplemented with ~13.0 µmol m -2 s -1 flux of UV-A 390 nm, and a total PPFD was ~125 µmol m -2 s -1 (16 h photoperiod) for 1 or 7 days before harvest, or entire growth period – 14 days. The results revealed that the influence of UV-A on growth and antioxidant properties depended on basil variety and duration of irradiation. Generally, UV-A irradiation for 7 days significantly (P ≤ 0.05) inhibited growth and hypocotyl elongation of green-leaf basils, and for 14 days of both basil varieties. No significant differences on leaf chlorophyll index were determined. However, leaf flavonol index significantly increased in green-leaf basils after 7 and 14 days UV-A irradiation. The total phenols ant anthocyanin contents significantly decreased after 1 day UV-A irradiation in purple-leaf basils, and the continuous decrease following UV-A irradiation for 7 or 14 days was determined. In addition, UV-A irradiation had negative effects on ABTS radical activity in purple-leaf basils; however, the significantly higher ABTS radical scavenging activity after UV-A irradiation for 1 or 7 days in green-leaf basils were determined. UV-A influenced higher ascorbic acid synthesis in purple-leaf basils after 7 days irradiation, or after 14 days irradiation in both basil varieties. In summary, the supplemental UV-A LED lighting allows to protect basil microgreens from hypocotyl elongation, and enhances antioxidant properties in green-leaf basils. Purple-leaf basils showed to be more sensitive to UV-A irradiation, and less positive effects on antioxidant properties were determined. Keywords: antioxidant, greenhouse, light emitting diode, microgreen, UV-A. Article DOI: http://doi.org/10.15544/RD.2015.0 31

Pulsed Light-Emitting Diodes for a Higher Phytochemical Level in Microgreens

A novel research of pulsed light-emitting diode (LED) lighting versus continuous lighting was conducted by analyzing phytochemical levels in microgreens. Red pak choi (Brassica rapa var. chinensis), mustard (Brassica juncea L.), and tatsoi (Brassica rapa var. rosularis) were grown indoors under HPS lamps supplemented with monochromatic (455, 470, 505, 590, and 627 nm) LEDs [total photosynthetic photon flux density (PPFD) of 200 ± 10 μmol m-2 s-1, for 16 h day-1]. For pulsed light treatments, the frequencies at 2, 32, 256, and 1024 Hz with a duty cycle of 50% monochromatic LEDs were applied. The results were compared to those under the continuous light (0 Hz) condition in terms of total phenolic content, anthocyanins, and antiradical activity (DPPH). The summarized data suggested that pulsed light affected accumulation of secondary metabolites both positive and negative in microgreens. The significant differences in the response of phytochemicals between pulsed light at several frequencies and continuous light were determined. The most positive effects of 2, 256, and 1024 Hz for total phenolic compounds in mustard under all wavelength LEDs were achieved. The LED frequencies at 2 and 32 Hz were the most suitable for accumulation of anthocyanins in red pak choi and tatsoi. The highest antiradical activity under the treatments of 32, 256, and 1024 Hz in mustard and under the 2 Hz frequency in red pak choi and tatsoi was determined.