Light emitting diodes (LEDs) of different wavelengths significantly influenced kale growth, morphology, and nutrient content. The importance of indoor agriculture is being recognized, but few studies have investigated the influence of LEDs, particularly green wavelengths, on crops at the transcriptome level. The objective of this study was to use RNA sequencing technology to elucidate the genetic response of kale to blue (BV), green (G), and red (RF) LEDs compared to the combination of all the LEDs (RFBVG), control. Results revealed total amount of differentially expressed genes (DEGs) was 1373 for kale grown under BV LEDs, 924 under G LED, and 133 under the RF LED treatments. DEGs enriched in kale grown under RF LEDs played roles in regulating hormone metabolic processes and oxidoreductase activity. In the BV treatment, several enzymes in the phenolic biosynthetic pathway were upregulated compared to the control which may explain previous results reporting higher levels of phenolic content in kale grown under BV LEDs. In the G LED treatment, the expression of genes related to photosynthesis, heme binding, and oxidoreductase activity were upregulated compared to those in the control group. These results may support previous findings of higher iron content in kale grown under G LEDs. Further, the G LED treatment upregulated the expression of cytochrome P450 enzymes, which play key roles in plant growth and stress responses. Understanding the molecular mechanisms underlying the effects of different LED wavelengths by RNAseq provides information to improve indoor cultivation practices that optimize crop growth and nutrient value.
There are contrasting effects of far-red (FR; 700–750 nm) light on leaf area and biomass in plants. These differences have been attributed to photon flux density (PFD) and species/cultivar differences. In a previous experiment, total PFD (TPFD) did not mediate the influence of FR light on leaf area and shoot mass when the TPFD alterations were only of red (R; 600–699 nm) and FR light. Therefore, we hypothesized that blue (B; 400–499 nm) light controls the influence of TPFD in regulating the effects of FR light on leaf area and shoot mass. We cultivated kale (Brassica oleracea var. sabellica) ‘White Russian’ and lettuce (Lactuca sativa) ‘Rex’ and ‘Rouxai’ under 12 lighting treatments with a 24 h∙d−1 photoperiod and TPFDs of 85, 170, 255, or 340 µmol∙m−2∙s−1 and FR fractions [FR-PFD divided by the sum of R and FR PFD] of 0.00, 0.17, or 0.33. The alterations in the TPFDs were solely due to B-PFD; the sum of R and FR PFD was constant in all treatments. Preliminary results indicate that elevated FR fraction did not increase leaf area and shoot mass of all three crops in the absence of B light, when the TPFD was 85 µmol∙m−2∙s−1. However, a high B-PFD and thus TPFD amplified the effects of a high FR fraction at increasing leaf area and shoot mass of all three cultivars. These high FR-fraction effects were correlated with increased biomass partitioning to leaves at a high B-PFD and thus TPFD. These results imply that the contrasting effects of FR light on leaf area and biomass in previous studies could be attributed to the B-PFD. In addition, the influence of TPFD on FR-fraction effects is primarily influenced by the B-PFD.
Light quality can regulate growth and quality characteristics of young plants, but responses of culinary herb transplants are not well understood. Blue light generally inhibits extension growth while far-red light promotes stem elongation and leaf expansion. The objective of this study was to investigate the interaction between blue (400-499 nm) and far-red (700-750 nm) light on six culinary herb species, basil ‘Nufar’, cilantro ‘Santo’, parsley ‘Giant of Italy’, sage ‘Extraka’, mint ‘Spearmint’, and oregano ‘Greek’, with the goal of producing high-quality transplants with compact growth. Six indoor lighting treatments were tested with blue light photon flux densities (PFDs) of 20, 60, or 100 µmol∙m−2∙s−1 and far-red light of 0 or 60 µmol∙m−2∙s−1, with red light (600-699 nm) added so that the total PFD was 210 µmol∙m−2∙s−1 in all treatments. Seeds were sown in 72-cell trays at a constant 23 °C under a 16-h photoperiod and grown for 28-44 days until harvest. As expected, treatments with the highest far-red and lowest blue light PFDs had the greatest extension growth and those with no far-red and high blue light were the most compact. Preliminary results indicate basil, cilantro, and mint exhibited the greatest leaf area under high blue and far-red light. Generally, all species had the highest shoot fresh mass when grown with far-red light. We conclude that blue light and far-red light interact to regulate plant height and leaf area, especially in basil and sage. Therefore, including blue and far-red in the light spectrum should be considered to manage the morphology of young culinary herb plants.
Substituting green (G; 500-600 nm) for blue (B; 400-500 nm) light can enhance crop yield through increasing leaf expansion and photon capture in indoor farming. In addition to yield, the concentration of phytochemicals may also be influenced by varying B to G light ratios. Those responses to B and G light are primarily mediated by cryptochrome photoreceptors. However, cryptochrome activity is further dependent on temperature. We hypothesized that B and G light and temperature could interactively regulate plant morphology, physiology, and secondary metabolites, consequently impacting crop yield and nutritional quality. Two cultivars of lettuce (Lactuca sativa L.), ‘Rouxai’ and ‘Rex’, were grown under three temperatures (20, 24, and 28 ℃) and five spectral treatments composed of B, G, and red (R; 600-700 nm) light (B40G0R60, B30G10R60, B20G20R60, B10G30R60, and B0G40R60). The subscript number following each light type represents its percentage in total photon flux density (TPFD; 400-800 nm). TPFD was maintained at a constant level of 200 μmol·m-2·s-1, with R photon flux of 120 μmol·m-2·s-1 (60% of TPFD) in all treatments. Results revealed that light spectra and temperature interactively influenced plant morphology. Specifically, in Rouxai, increasing G light from 0% to 40%, coupled with decreasing B from 40% to 0%, linearly increased total leaf area at all three temperatures. Notably, the substitution of G for B light caused the greatest leaf expansion at 24 ℃ (a 64% increase at 20 ℃, a 90% increase at 24 ℃, and a 32% increase at 28 ℃). In Rex, substituting G light for B light up to 30% increased total leaf area at 20 and 24 ℃, but not at 28 ℃. Similar to Rouxai, the spectral effect on the leaf expansion of Rex was greater at 24 ℃, compared to 20 ℃. Shoot dry weight responded to spectral and temperature treatments similarly as total leaf area. Secondary metabolites (e.g., phenolics and flavonoids) and antioxidant capacity consistently decreased with increasing G light (or decreasing B from 40% to 0%), but the decline was more pronounced at warmer temperatures. Without significant interaction between light spectrum and temperature, chlorophyll and carotenoid contents decreased with increasing G light. Thus, we concluded that the proportion of B and G light and temperature interactively regulated plant morphology and secondary metabolites, ultimately affecting crop yield and nutritional quality. Our study emphasizes the importance of considering the interaction between light spectrum and temperature in optimizing production systems.
Growing food crops in space supports astronauts’ dietary needs in long-duration space missions and necessitates efficient use of light. In red-leaf lettuce (Lactuca sativa), sufficient red (R) and far-red (FR) light promote extension growth, whereas sufficient blue (B) light restricts extension growth but enhances secondary metabolite accumulation. Green (G) light also contributes to photosynthesis and improves visual quality. Compared to fixed light spectra, we evaluated dynamic light spectra to balance harvestable biomass and nutritional quality of red-leaf lettuce ‘Outredgeous’ under elevated CO2 concentration (≈2794 μmol⋅mol–1) and intermediate relative humidity (≈48%), typical on the International Space Station. This ground-based growth chamber experiment was performed twice following a randomized complete block design. We grew plants hydroponically at ≈22 °C under light-emitting diodes (LEDs) with four fixed light spectra and four dynamic light-spectrum alternations. The four fixed light spectra from seed to harvest were B60R140, B10R190, B10G50R140, and B10R140FR50 (the subscript following each waveband denotes its photon flux density in μmol·m−2·s−1). The four dynamic light-spectrum alternations switched among B10R190, B10G50R140, and B10R140FR50 in the lag (day 0–11) and exponential growth (day 11–25) phases, followed by B60R140 in the finish phase (day 25–28). Plant data were collected 11 and 28 days after sowing for seedlings and mature plants, respectively. Among the fixed light spectra, increasing the B photon flux density decreased shoot mass by 28% to 39% but increased total phenolic concentration by 27% to 45% in mature plants. Partial substitution of R light with G light decreased shoot mass by 31% to 42% in seedlings, but not mature plants. Partial substitution of R light with FR light did not influence shoot mass of seedlings or mature plants. Compared with fixed low B light treatments, dynamic light-spectrum alternations with high B light in the finish phase did not affect shoot mass, root mass, or leaf number while increasing total phenolic concentration by 8% to 25%. In addition, partial substitution of R light with G or FR light during the lag or exponential growth phase did not influence shoot or root mass. We conclude that low B light in the lag and exponential growth phases followed by short-term high B light in the finish phase improves lettuce nutritional quality without decreasing biomass as seen under long-term high B light. Spectrum selection in the earlier phases should prioritize the photosynthetic photon efficacy of LEDs to maximize light use efficiency.
Tomato production under controlled environmental conditions presents challenges due to the selective permeation of solar radiation within enclosed structures or the limited wavelengths produced by artificial light sources. Despite these challenges, growers increasingly opt for such production systems due to the enhanced uniformity and yield of fruit compared to open-field cultivation. However, controlled environment conditions, particularly greenhouses, often limit specific wavelengths of light, including blue and UV-B radiation. This limitation has the potential to alter flavor and overall fruit quality. Therefore, the present investigation examined how supplemental blue and UV-B light, independently and in combination, influence the levels of amino acid–derived flavor compounds, particularly those derived from branched-chain and aromatic amino acids, in two tomato varieties, Plum Regal (PR, commercial) and TAM HOT-Ty (THT, Texas A
Managing water loss of unrooted cuttings (URC) during acclimation is critical to decrease crop losses and shorten rooting time. Vertical indoor propagation (VIP) systems that use indoor-farming technologies enable the opportunity to optimize the environment for URC acclimation. However, recommend environmental setpoints for VIP systems are unknown. Light quality affects various morphological and physiological processes in plants, and blue light in particular, has an effect on stomatal opening and plant size, both of which regulate water relations of plants. Therefore, the objective of this study was to characterize short-term effects of increasing percentages of blue light on water relations of Chrysanthemum ‘Crystal Bright’ and Begonia ‘Dark Britt’ URC. Four light-quality treatments were evaluated: 15%, 30%, 45%, or 60% blue light. All treatments provided a photosynthetic photon flux density of 70 µmol·m–2·s–1 delivered by broadband and monochromatic-blue light-emitting diode fixtures. Ambient temperature, relative humidity, and carbon dioxide concentration were set at 22 °C, 70%, and 420 μmol·mol–1. Water uptake and water loss were evaluated by placing individual URC in vials with and without water, and exposing them to each treatment for 24 or 48 h, respectively. Changes in water loss were also recorded at various intervals for 24 h. Water uptake of Chrysanthemum linearly increased as blue-light percentages increased. In contrast, water uptake followed a quadratic response for Begonia, which peaked at 45% blue light. Water loss also followed a quadratic response for begonia, with increasing values up to 30% blue light. Water loss of Chrysanthemum followed linear response to increasing blue light. After 24 h, water loss of Chrysanthemum linearly increased with increasing blue light, from 0.65 to 0.76 g under 15% and 60% blue light, respectivey. There were no treatment differences for stomatal conductance, but leaf vapor pressure deficit linearly increased with increasing blue light, regardless of species. These findings show that blue light affects water relations of URC, which should be considered when making lighting recommendations for VIP systems.
Brassica plants contain important secondary metabolites, such as glucosinolates, and provide a nutritious addition to the human diet. Glucosinolates, when hydrolyzed, yield isothiocyanates which can affect the carcinogenesis process, and further research into increasing glucosinolate concentrations in plants is important for determining anticarcinogenic properties of brassicas in human diets. Kale (Brassica oleracea var. acephala cv. ‘Toscano’ ) and Arabidopsis (Arabidopsis thaliana, Col-0) were grown in the greenhouse under natural light (control) and subjected to three additional supplemental light treatments to determine the impact of supplemental LED lighting on glucosinolate concentrations. Treatments included no supplemental light (control), 75:25 Red:Blue LED, 50:50 Red:Blue LED, and Warm White LED light at 100 μmol.m-2.s-1 each. Plants were harvested when the first kale treatment group reached a leaf number of 7, and when half of all Arabidopsis flowers began opening. Harvested plants were analyzed for glucosinolate and mineral nutrient concentration. Statistical analysis on Arabidopsis data revealed significant differences among light treatments in glucosinolate concentrations, particularly glucoraphanin and gluconasturtiin. Additionally, significant differences were found in leaf and petiole mass and leaf number of both kale and Arabidopsis at harvest. The no supplemental light control produced the lowest harvest mass compared to plants receiving supplemental light. Preliminary qPCR analysis of Arabidopsis displays variations in the relative expression of genes CYP79B2 and CYP83A1, varying across treatment when compared to the control. Glucosinolate analysis of kale resulted in no statistically significant differences among all four light treatments. However, glucosinolates, including gluconapin, glucoraphanin, gluconasturtiin, and several unknowns, were found to be present across all four treatments. As glucosinolates are stress-response compounds, their lack of variation in kale and significant variation in Arabidopsis under different light environments indicate that other environmental factors also play a crucial role in their production. Further research is necessary to identify abiotic and biotic factors influencing their concentration in the greenhouse environment for both species.
