This study examines the impact of daily light integral (DLI) from artificial lighting on tomato seedlings cultivated in plant factories. By adjusting the light intensity and photoperiod of LED, the research explored the effects of varying DLIs on the morphology, growth, physiological characteristics, photosynthetic pigment content, and chlorophyll fluorescence of tomato seedlings. The optimal DLI enhanced seedling growth, biomass, root vitality, antioxidant enzyme activity, and photosynthetic pigment synthesis. Excessively high DLI or light intensity inhibited photosynthesis, potentially leading to photoinhibition. This study identified the optimal DLI of 13.2 mol·m⁻²·d⁻¹ through varying DLI gradients in Exp 1 and Exp 2. Based on these findings, Exp 3 established the optimal growth conditions by setting different light intensities and photoperiods under the most suitable DLI, which were a light intensity of 200 μmol·m⁻²·s⁻¹ and a photoperiod of 18 h. These results provide significant guidance for optimizing the light environment in the cultivation of tomato seedlings in plant factories, helping to improve the light energy utilization efficiency.

The understanding of the supplementation scheme of red (R) and far-red (FR) light in the cultivation of leafy vegetables in plant factories with artificial lighting (PFALs) is still limited. This study investigated the effects of supplemental R and FR light at different plant growth stages on the morphology, growth characteristics, and nutritional properties of lettuce. Supplemented R + FR throughout the entire growth stages was beneficial for the growth of lettuce, for which the total fresh weight was increased by 53.76%, and it also enhanced the content of soluble sugars by 39.98% and vitamin E by 34.21%. The pre-supplementation of FR light followed by supplementation of R light at various growth stages not only increase the total fresh weight of lettuce by 26.10% but also ensured that most nutritional indices did not decrease, and it even increased the content of soluble sugars by 35.24% while decreasing the nitrate content by 31.52%. The scheme of pre-supplementation of R light followed by the supplementation of FR light promoted a more upright plant architecture in lettuce, which was advantageous for improving the cultivation density of lettuce in plant factories with artificial lighting, thereby enhancing the yield/m². Moreover, it could increase the vitamin E content of lettuce. The growth and nutritional properties of lettuce exhibit significant effects under different supplementation methods of R and FR light. In PFALs, the selection of different light supplement schemes also requires a careful balance between yield and quality. From an energy-saving perspective, the pre-supplementation of FR light followed by supplementation of R light at various plant growth stages is beneficial for lettuce production in PFALs.

Far-red lights (FRs), with a wavelength range between 700 and 800 nm, have substantial impacts on plant growth, especially horticultural crops. Previous studies showed conflicting results on the effects of FRs on vegetable growth and quality. Therefore, we conducted a meta-analysis on the influence of FRs on vegetable growth, aiming to provide a comprehensive overview of their effects on the growth and nutritional indicators of vegetables. A total of 207 independent studies from 55 literature sources were analyzed. The results showed that FR treatment had significant effects on most growth indicators, including increasing the fresh weight (+25.27%), dry weight (+21.99%), plant height (+81.87%), stem diameter (+12.91%), leaf area (+18.57%), as well as reducing the content of chlorophyll (−11.88%) and soluble protein (−11.66%), while increasing soluble sugar content (+19.12%). Further subgroup analysis based on various factors revealed significant differences in the effects of FR on different physiological indicators, such as FR intensity, plant species, duration of FR exposure, and the ratio of red light to FR. In general, moderate FR treatment is beneficial for vegetable growth. This study provides important references and guidelines for optimizing the application of FR in the future.

The purple tomato variety ‘Indigo Rose’ (InR) is favored due to its bright appearance, abundant anthocyanins and outstanding antioxidant capacity. SlHY5 is associated with anthocyanin biosynthesis in ‘Indigo Rose’ plants. However, residual anthocyanins still present in Slhy5 seedlings and fruit peel indicated there was an anthocyanin induction pathway that is independent of HY5 in plants. The molecular mechanism of anthocyanins formation in ‘Indigo Rose’ and Slhy5 mutants is unclear. In this study, we performed omics analysis to clarify the regulatory network underlying anthocyanin biosynthesis in seedling and fruit peel of ‘Indigo Rose’ and Slhy5 mutant. Results showed that the total amount of anthocyanins in both seedling and fruit of InR was significantly higher than those in the Slhy5 mutant, and most genes associated with anthocyanin biosynthesis exhibited higher expression levels in InR, suggesting that SlHY5 play pivotal roles in flavonoid biosynthesis both in tomato seedlings and fruit. Yeast two-hybrid (Y2H) results revealed that SlBBX24 physically interacts with SlAN2-like and SlAN2, while SlWRKY44 could interact with SlAN11 protein. Unexpectedly, both SlPIF1 and SlPIF3 were found to interact with SlBBX24, SlAN1 and SlJAF13 by yeast two-hybrid assay. Suppression of SlBBX24 by virus-induced gene silencing (VIGS) retarded the purple coloration of the fruit peel, indicating an important role of SlBBX24 in the regulation of anthocyanin accumulation. These results deepen the understanding of purple color formation in tomato seedlings and fruits in an HY5-dependent or independent manner via excavating the genes involved in anthocyanin biosynthesis based on omics analysis.

The effects of supplemental UV-A (385 nm) period and UV-A intensity for 5 days before harvest (DBH) on growth, antioxidants, antioxidant capacity, and glucosinolates contents in Chinese kale (Brassica oleracea var. alboglabra Bailey) were studied in plant factory. In the experiment of the UV-A period, three treatments were designed with 10 W·m⁻² UV-A supplement, T1(5 DBH), T2 (10 DBH), and no supplemental UV-A as control. In the experiment of UV-A intensity, four treatments were designed with 5 DBH, control (0 W·m⁻²), 5 w (5 W·m⁻²), 10 w (10 W·m⁻²), and 15 w (15 W·m⁻²). The growth light is as follows: 250 μmol·m⁻²·s⁻¹; red light: white light = 2:3; photoperiod: 12/12. The growth and quality of Chinese kale were improved by supplemental UV-A LED. The plant height, stem diameter, and biomass of Chinese kale were the highest in the 5 W·m⁻² treatment for 5 DBH. The contents of chlorophyll a, chlorophyll b, and total chlorophyll were only highly increased by 5 W·m⁻² UV-A for 5 DBH, while there was no significant difference in the content of carotenoid among all treatments. The contents of soluble sugar and free amino acid were higher only under 10 DBH treatments than in control. The contents of total phenolic and total antioxidant capacity were the highest in 5 W·m⁻² treatment for 5 DBH. There was a significant positive correlation between total phenolic content and DPPH and FRAP value. After 5 DBH treatments, the percentages and contents of total aliphatic glucosinolates, sinigrin (SIN), gluconapin (GNA), and glucobrassicanapin (GBN) were highly increased, while the percentages and contents of glucobrassicin (GBS), 4-methoxyglucobrassicin (4-MGBS), and Progoitrin (PRO) were significantly decreased, especially under 10 W·m⁻² treatment. Our results show that UV-A LED supplements could improve the growth and quality of Chinese kale, and 5 W·m⁻² UV-A LED with 5 DBH might be feasible for Chinese kale growth, and 10 W·m⁻² UV-A LED with 5 DBH was better for aliphatic glucosinolates accumulation in Chinese kale.

This study investigated the effects of substituting B with FR and UVA (50 μmol·m⁻²·s⁻¹) at two growth stages on the growth and quality of loose-leaf lettuce (cv. Fangni). The basal light was red and blue LEDs at 250 μmol·m⁻²·s⁻¹. At stage I (the first 10 days of 20-day pre-harvest), there were three treatments: B substituted by FR (FR); B substituted by UVA (UVA); and no substituting (CKI). At stage II (next ten days after stage I), there were 9 treatments: FF (FR + FR), UF (UVA + FR), BF (B + FR), FU (FR + UVA), UU (UVA + UVA), BU (B + UVA), FB (FR + B), UB (UVA + B), and B + B (CKII). At stage I, compare with UV-A and CKI, the shoot fresh weight, leaf area, leaf width, leaf length, and vitamin C content highly increased under far-red light (FR), whereas specific leaf weight and the chlorophyll contents significantly decreased by FR. In CKI, nitrate contents and the antioxidant capacity (FRAP, DPPH) were significantly higher than in FR and UVA. At stage II, higher leaf width, leaf length, leaf area, and shoot fresh and dry weight were observed in FF, UF, and BF. The lowest biomass was shown in CKII. Higher chlorophyll contents were found in FU and FB. The soluble sugar contents significantly increased by all treatments. In addition to UB and BU, soluble protein contents increased by other treatments. There were higher vitamin C contents in UU, UB, and CKII. Large amounts of nitrates accumulated under CKII. The higher antioxidant capacity (DPPH, FRAP) was found in FB and CKII. The highest flavonoid content was found in UB, and higher polyphenols contents were found in UB and BU. In this study, substituting B with FR at 2 stages were the best way to increase lettuce biomass. The optimal measure to both increased lettuce nutrition quality and biomass was FB at stage II.