Different intensities of UV-A (6, 12, 18 μmol·m⁻²s⁻¹) were applied in a plant factory to evaluate the combined influences of supplemental UV-A and red and blue light (Red:Blue = 1:1 at PPFD of 250 μmol·m⁻² s⁻¹) on the biomass, antioxidant activity and phytochemical accumulation of kale. Supplemental UV-A treatments (T1: 6 μmol·m⁻² s⁻¹, T2: 12 μmol·m⁻² s⁻¹ and T3: 18 μmol·m⁻² s⁻¹) resulted in higher moisture content, higher pigment content, and greater leaf area of kale while T2 reached its highest point. T2 treatment positively enhanced the antioxidant capacity, increased the contents of soluble protein, soluble sugar and reduced the nitrate content. T1 treatment markedly increased the content of aliphatic glucosinolate (GSL), whereas T2 treatment highly increased the contents of indolic GSL and total GSL. Genes related to GSL biosynthesis were down-regulated in CK and T3 treatments, while a majority of them were greatly up-regulated by T1 and T2. Hence, supplemental 12 μmol·m⁻² s⁻¹ UV-A might be a promising strategy to enhance the growth and quality of kale in a plant factory.

Crop breeding for high yields and quality is an important measure to ensure food security. In conventional breeding, a long generation time is required. Speed breeding could accelerate the flowering and fruiting of crops by providing suitable environmental conditions in order to reduce the generation times. This study aimed to determine a speed breeding scheme for hot peppers. Two hot pepper varieties, ‘Xiangyan 55’ and ‘Xiangla 712’, were investigated for their growth and development under different light intensities, photoperiods, and red-to-far-red ratios. Hot pepper plants bloomed at 39.88 ± 0.74 days after sowing under photosynthetic photon flux density (PPFD) 420 µmol·m⁻²·s⁻¹ and a 12-h photoperiod and had seed with acceptable germination rates at 82 days after sowing. Blooming was 2–3 days earlier when the photoperiod was extended to 20 h, but the fruit and seed development were not significantly improved. Supplementation of far-red light (R:FR = 2.1) significantly accelerated the red ripening of pepper fruit and improved seed germination rates. The modification of the light environment accelerated hot pepper growth and development, reduced breeding cycles, and could produce up to four generations per year.

The effects of different ratios of red:white light on the biomass, photosynthetic capacity, phytochemical accumulation, and antioxidant capacity of pak choi were investigated. There were three treatments: red:white = 1:2 (LR), red:white = 1:1 (MR), red:white = 2:1 (HR) with white light as control (CK) at photosynthetic photon flux density (PPFD) of 250 μmol·m⁻²·s⁻¹. In LR treatment, chlorophyll fluorescence and nitrate content were reduced, while the photosynthetic rate (Y(ll)), the contents of soluble protein, soluble sugar, vitamin C, flavonoids, polyphenols, glucosinolates, FRAP, and 2,2-diphenyl-1-bitter acyl radical scavenging increased. The chlorophyll content was enhanced in MR treatment, and the photosynthetic rate and glucosinolate content increased in HR treatment. The most suitable light for the cultivation of pak choi in the plant factory was red:white = 1:2.

To explore the effect of different nutrient-solution depths on the growth and phytochemicals accumulation of kale, three different nutrient-solution depth treatments (De-1: 1 cm, De-2: 2 cm, and De-3: 3 cm) were applied in the plant factory with artificial lighting. The maximum levels of plant height, stem diameter, total leaf area, total root length, and root surface area as well as fresh and dry weight of the shoot and root were all noted in De-2 at 24 days after treatment. Low nutrient-solution depth treatments (De-1 and De-2) were beneficial for total chlorophyll accumulation and nutrient ions uptake (N, P, K, Ca, S, and Zn). However, there were no obvious differences in DPPH and FRAP as well as contents of total polyphenols and flavonoids. In high nutrient-solution depth treatment (De-3), the contents of carotenoid, soluble sugars, and vitamin C were higher than those in De-1 and De-2. The contents of total glucosinolates (GLs), aliphatic GLs, and indole GLs significantly increased in kale under De-3. Higher contents of reactive oxygen species (ROS), hydrogen peroxide (H₂O₂), oxalate oxidase (OXO), and proline were observed in kale roots under De-2 and De-3. Overall, 2 cm of nutrient-solution depth could be used to promote kale growth, and 3 cm may represent a potential approach for improving kale quality in a plant factory.

As an indispensable element in the morphology and phytochemical profile of plants, UV-A has proved to help promote the growth and quality of kale. In this study, UV-A supplementation in different photoperiods (light period supplemental UVA = LS, dark period supplemental UVA = DS, and light-dark period supplemental UVA = LDS) contributed to yielding greater biomass production (fresh weight, dry weight, and plant moisture content), thus improving morphology (plant height, stem diameter, etc.) and promoting higher phytochemicals content (flavonoids, vitamin c, etc.), especially glucosinolates. To fathom its mechanisms, this study, using RNA-seq, verified that UV-A supplementation treatments signally generated related DEGs of plant hormone signal pathway, circadian rhythm plant pathway, glucosinolate pathway, etc. Moreover, 2047 DEGs were obtained in WGCNA, illustrating the correlations between genes, treatments, and pathways. Additionally, DS remarkedly up-regulated related DEGs of the key pathways and ultimately contributed to promoting the stem diameter, plant height, etc., thus increasing the pigment, biomass, vitamin c, etc., enhancing the antioxidant capacity, and most importantly, boosting the accumulations of glucosinolates in kale. In short, this study displayed new insights into UV-A supplementation affected the pathways related to the morphology and phytochemical profile of kale in plant factories.

The nutritional quality and biomass of various sprouts can be enhanced by Zn and red-blue light, especially the Brassica sprouts. However, the combined effects of this two on sprouts are rarely reported. In this study, different Zn concentrations (0, 1.74, 3.48, 10.43 and 17.39 mM) were combined with two ratios of red-blue light-emitting diodes (LEDs) (R: B = 1:2, 1R2B; R: B = 2:1, 2R1B, at 70 μmol m⁻² s⁻¹ PPFD, 14 h/10 h, light/dark) to investigate their mutual effects on the growth, mineral elements, and nutritional quality in flowering Chinese cabbage sprouts (FCCS). Fresh weight, dry weight, contents of organic Zn, soluble sugar, vitamin C, total flavonoids, total polyphenol, FRAP (ferric ion-reducing antioxidant power) and DPPH (radical inhibition percentage of 1,1-diphenyl-2-picrylhydrazyl) were significantly increased by Zn supplement (10.43 and 17.39 mM) and 2R1B, while hypocotyl length and moisture content were decreased remarkably by Zn supplement. Total glucosinolates contents in the sprouts increased dramatically under 2R1B compared with 1R2B, while photosynthetic pigments contents decreased. Heat map and principal component analysis showed that 2R1B + 17.39 mM Zn was the optimal treatment for the accumulation of biomass and health-promoting compound in FCCS, suggesting that a suitable combination of light quality and Zn supplement might be beneficial to zinc-biofortified FCCS production.