End-of-production Ultraviolet A and Blue Light Similarly Increase Lettuce Coloration and Phytochemical Concentrations

Kelly, Nathan; Runkle, Erik S.

doi:10.21273/hortsci17108-23

Cited by 5 publications

(6 citation statements)

References 47 publications

(65 reference statements)

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“…1, Tables 1 and 2), regardless of when they were delivered, consisted of 30 mmolÁm À2 Ás À1 of UVA (peak 5 386 nm), 30 mmolÁm À2 Ás À1 of B (peak 5 449 nm), or 20 mmolÁm À2 Ás À1 of R and 10 mmolÁm À2 Ás À1 of green (G; peak 5 532 nm) light, which increased the TPFD to 180 mmolÁm À2 Ás À1 for at least one phase of the experiment (Table 1). We used 30 mmolÁm À2 Ás À1 of UVA or B light because the PFD elicited plant quality improvements during previous experiments (Kelly and Runkle 2023), and that was the maximum UVA intensity that the lighting fixtures could deliver. We evaluated one treatment with no supplemental lighting (control), one with R1G light applied during all three phases to act as another control at a higher TPFD without increasing the PFD of B light, one with UVA and one with B applied during all three phases, and six treatments with either UVA or B light applied during one of the three phases (Table 2).…”

Section: Methodsmentioning

confidence: 99%

“…On days 12, 20, and 28, we collected leaf tissue from three randomly selected plants from each treatment for the TPC and TAC analysis. For the TPC analysis, we collected 0.5 g of light-exposed fresh leaf tissue from each biological sample (experimental unit), immediately froze it in liquid nitrogen, and processed and analyzed samples spectrophotometrically according to the protocol used by Kelly and Runkle (2023), which was based on the protocol used by Ainsworth and Gillespie (2007), with slight modifications. Similarly, for the TAC analysis, we collected 0.3 g of light-exposed fresh leaf tissue from each biological sample, froze it in liquid nitrogen, and processed and analyzed the samples using a modified version of the Lee et al (2005) pH differential method (AOAC Official Method 2005.2) described by Kelly and Runkle (2023).…”

Section: Methodsmentioning

confidence: 99%

“…For the TPC analysis, we collected 0.5 g of light-exposed fresh leaf tissue from each biological sample (experimental unit), immediately froze it in liquid nitrogen, and processed and analyzed samples spectrophotometrically according to the protocol used by Kelly and Runkle (2023), which was based on the protocol used by Ainsworth and Gillespie (2007), with slight modifications. Similarly, for the TAC analysis, we collected 0.3 g of light-exposed fresh leaf tissue from each biological sample, froze it in liquid nitrogen, and processed and analyzed the samples using a modified version of the Lee et al (2005) pH differential method (AOAC Official Method 2005.2) described by Kelly and Runkle (2023). Additionally, on days 12, 20, and 28, we used the same three plants used for the biochemical analysis to measure relative chlorophyll concentration using a soil plant analysis development (SPAD) meter (SPAD-502; Konica Minolta Sensing, Inc., Osaka, Japan) by measuring and averaging three spots on one fully expanded leaf exposed to direct light.…”

Section: Methodsmentioning

confidence: 99%

“…For instance, FR light could be applied to lettuce seedlings to promote early leaf expansion, allowing for greater light interception and subsequent photosynthesis later in production (Klassen et al 2003;Legendre and van Iersel 2021;Park and Runkle 2017). Alternatively, UVA or B light can be delivered at the end of production (EOP) to increase the total anthocyanin concentration (TAC) and subsequent leaf pigmentation of lettuce (Chen et al 2019;Kelly and Runkle 2023;Owen and Lopez 2015). In addition, the delivery of short-wavelength light at the EOP has a limited or no effect on suppressing extension growth or biomass accumulation (Chen et al 2019).…”

mentioning

confidence: 99%

“…Although studies have reported favorable results with EOP lighting on indoor-grown leafy greens (Chen et al 2019;Hooks et al 2021Hooks et al , 2022Kelly and Runkle 2023), we are not aware of studies that have directly compared EOP lighting to continuously applied lighting of the same spectrum or for different phases of production (e.g., seedling stage or middle of production) to determine if there are any persistent effects on harvested lettuce. Therefore, the objectives of this study were to determine when UVA or B light could be applied during production to increase lettuce quality and nutritional attributes and whether EOP UVA or B light is as effective at increasing lettuce phytonutrients and leaf pigmentation as applying UVA or B light during the entire production cycle.…”

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confidence: 99%

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Ultraviolet A and Blue Light Transiently Regulate Total Phenolic and Anthocyanin Concentrations in Indoor-grown Red-leaf Lettuce

Kelly,

Runkle

2023

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In controlled environments, supplementing a light spectrum with ultraviolet A (UVA; 315–399 nm) or blue (B; 400–499 nm) light increases the concentrations of phenolic compounds that can increase quality attributes, such as leaf pigmentation and nutritional quality of lettuce (Lactuca sativa). However, B light and sometimes UVA light can inhibit leaf expansion and biomass accumulation when continuously applied, whereas applying it only at the end of the production cycle can increase lettuce quality with little to no effect on crop yield. Our objective was to quantify the persistency of periodic supplemental UVA or B light and compare end-of-production with continuously applied supplemental light during indoor lettuce production on quality attributes and biomass accumulation. We hypothesized that supplemental UVA or B light would be more effective later, rather than earlier, during production with increasing lettuce quality attributes. We grew ‘Rouxai’ red-leaf lettuce hydroponically at an air temperature of 23 °C under 75 μmol⋅m−2⋅s−1 of red (peak = 664 nm) plus 75 μmol⋅m−2⋅s−1 of warm-white light provided by light-emitting diodes. The supplemental lighting treatments consisted of adding 30 μmol⋅m−2⋅s−1 of UVA (peak= 386 nm) or B (peak = 449 nm) light during the seedling phase (P1; days 4–12), growth phase (P2; days 12–20), finishing phase (P3; days 20–28), or the entire time (ET; days 4–28). Supplemental UVA or B light applied at any individual phase did not inhibit biomass accumulation, whereas enriched B light during the entire production period inhibited fresh mass compared with no supplemental light. Additionally, supplemental UVA or B light during P3 or ET similarly increased total phenolic and anthocyanin concentrations. Finally, applying UVA or B light during P1 or P2 had no residual effect on mature plant growth or quality at harvest. We concluded that the end of the production cycle is the optimal time to apply supplemental UVA or B light to improve lettuce coloration and phenolic content, that earlier application elicits transient responses, and that continuous application improves lettuce quality but inhibits biomass accumulation. Finally, there are potential energy savings by using end-of-production supplemental light compared with continuous application of the same spectrum.

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Section: Methodsmentioning

confidence: 99%