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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.

Effects of illumination spectrum on the morphogenesis of chrysanthemum plantlets (Chrysanthemum morifolium Ramat. 'Ellen') grown in vitro were studied using an illumination system consisting of four groups of light-emitting diodes (LEDs) in the following spectral regions: blue (450nm), red (640nm), red (660nm), and far-red (735nm). Taking into account all differences in shoot height, root length, and fresh and dry weight (FW and DW, respectively), observed while changing the total photon flux density (PFD), the optimal total PFD for growth of chrysanthemum plantlets in vitro was estimated. For 16 h photoperiod and typical fractions of the spectral components (14%, 50%, 28%, and 8%, respectively), the optimal total PFD was found to be 40 µmol m -2 s -1. Our study shows that the blue component in the illumination spectrum inhibits the plantlet extension and formation of roots and simultaneously increases the DW to FW ratio and content of photosynthetic pigments. We demonstrate photomorphogenetic effects in the blue region and its interaction with the fractional PFD of the far-red spectral component. Under constant fractional PFD of the blue component, the root number, length of roots and stems, and fresh weight of the plantlets have a correlated nonmonotonous dependence on the fractional PFD of the far-red component.

BACKGROUND The effect of light quality on phytochemicals in romaine baby leaf lettuce ‘Thumper’ was investigated in (I) a closed environment and (II, III) a greenhouse (16 h, 21/17 °C): (I) basal (638, 455, 660, 735 nm) LEDs supplemented with UV (380 nm), green (510 nm), yellow (595 nm) or orange (622 nm) LEDs (PPFD of ∼175 µmol m−2 s−1); (II) high‐pressure sodium (HPS) lamps (90 µmol m−2 s−1) supplemented with blue (455, 470nm) or green (505, 530nm) LEDs (30 µmol m−2 s−1); (III) at 3 days before harvesting, HPS lamps (90 µmol m−2 s−1) supplemented with red (638 nm) LEDs (210 µmol m−2 s−1). RESULTS (I) Supplemental UV or orange light enhanced phenolic compounds, supplemental UV or green light enhanced α‐carotene, and supplemental green light enhanced anthocyanins. All supplemental LED colours had a negative effect on tocopherol and ascorbic acid levels. (II) HPS lighting supplemented with different LEDs was not efficient, since the increase in some compounds did not compensate the decrease in major tested phytochemicals. (III) Short‐term irradiation with supplemental 638 nm LEDs before harvesting in the greenhouse did not have a significant effect on phytochemical contents, apart from enhancing tocopherols. CONCLUSION Wavelength control using LED technology affects the production of secondary metabolites, as the metabolism of many nutrients is light‐dependent. The narrow‐bandwidth supplemental light effects were diminished by broader‐spectrum HPS light or natural daylight in the greenhouse. © 2013 Society of Chemical Industry

In vitro conditions for Japanese quince polyploidisation were investigated. Microshoots and isolated cotyledons were treated with colchicine and oryzalin. Morphogenesis was more dependent on the concentration of colchicine or oryzalin than on the duration of exposure, genotype differences were observed. Low oryzalin concentrations had no impact on morphogenesis. Plants with changed chromosome numbers were obtained at 0.25-38 mM colchicine and 10-50 lM oryzalin concentrations. It was determined that stomata length is a suitable parameter for identifying putative Japanese quince tetraploids. Stomata of tetraploid shoots of the same clone were approximately 1/3 longer than in the diploids. It was shown that through polyploidisation gigas effect was not obtained in fruit size but tetraploids have reduced seed set and an increased proportion of fruit flesh.

The purpose of this study was to evaluate the role of 638-nm and 665-nm LEDs on changes of antioxidants of basil (Ocimum basilicum) and parsley (Petroselinum crispum), and to assess the effect of light quality on antioxidative status. Plants were grown in peat substrate for 19 days (21/17 ±2°C, 16 h). Experiments were performed in (I) a controlled-environment: B455,R638,R665,FR731(control); B455,R*638,R665,FR731; B455,R638,R*665,FR731; R638; R665 (B–blue, R- red, FR–far-red light). PPFD was set from 231 during growth, upto 300 μmol m-2 s-1 during 3-day treatment changing R638 or R665 PPFD level; in (II) greenhouse (November): high-pressure sodium lamps (HPS) (control—300 μmol m−2s−1); and HPS + 638 (HPS generated 90 and red LEDs—210 μmol m−2s−1). In general, under supplemental or increased red 638 nm light, amounts of tested antioxidants were greater in basil, whereas sole 665 nm or sole 638 nm is more favourable for parsley. Increased or supplemental red light significantly increased contents of phenolics, α-tocopherol, ascorbic acid and DPPH• but suppressed accumulation of lutein and β-carotene in basil, whereas an increase of β-carotene and DPPH• was observed in parsley. Hereby, the photoresponse of antioxidant compounds suggests that photoprotective mechanism is stimulated by both light-dose-dependent and wavelength-dependent reactions.