The alterable light/dark cycle in a plant factory with artificial lighting eliminates the traditional concept of day and night in nature. Adjusting the light/dark cycle to closely align with the inherent circadian rhythm of plants can enhance biomass accumulation. In this study, we examined the effects of different light/dark cycles on the photosynthetic performance, growth, and energy use efficiency of two hydroponic lettuce cultivars (Lactuca sativa L. cv. ‘Frillice’ and ‘Crunchy’). The lettuces were subjected to four light/dark cycle treatments—16 h light/8 h dark (L₁₆D₈, as control), 12 h light/6 h dark (L₁₂D₆), 8 h light/4 h dark (L₈D₄), and 4 h light/2 h dark (L₄D₂), all under LED lamps with white combined red chips at the same light intensity of 250 μmol m⁻² s⁻¹. Photosynthetic performance and growth index were measured during the slow and rapid growth stages, corresponding to days 9 and 21 after transplanting, respectively. For Frillice, L₁₂D₆ achieved the highest shoot dry weight and light and electricity energy use efficiencies on days 9 and 21 after transplanting, primarily due to the largest leaf area, leaf number, and net photosynthetic rate. For Crunchy, L₁₂D₆ and L₈D₄ increased shoot fresh and dry weights due to larger leaf area and leaf number on day 9 after transplanting compared with L₁₆D₈. Subsequently, the lettuces in L₁₆D₈ exhibited a rapid increase in leaf area and leaf number, along with a high net photosynthetic rate during the rapid growth stage, resulting in fast shoot biomass accumulation. There were no significant differences in the shoot dry weight and energy use efficiency between L₁₆D₈ and L₁₂D₆ on day 21 after transplanting. Two lettuce cultivars in L₁₆D₈ both exhibited the highest water use efficiency on day 21 after transplanting. In conclusion, the light/dark cycle lighting can alter lettuce biomass accumulation by modifying plant morphology and leaf net photosynthetic rate. Additionally, the physiological response to the light/dark cycle was cultivar-dependent. Our findings provide valuable insights for optimizing hydroponic lettuce production to achieve high yield in LED plant factories.

Conventional wheat breeding in the field is limited to two generations per year and is susceptible to environmental fluctuations. Speed-breeding in a plant factory offers a solution; however, recommendations for lighting strategies remain limited. To identify the optimal daily light integral (DLI) for the seedling stage, we tested three light intensities (300, 500, and 700 μmol m⁻² s⁻¹) and four photoperiods (10, 14, 18, and 22 h d⁻¹), resulting in DLIs ranging from 10.8 to 55.4 mol m⁻² d⁻¹. Our results indicated that an optimal DLI of 39.6 mol m⁻² d⁻¹ was associated with the highest seedling index (0.26) and root-to-shoot ratio (0.42), as well as enhanced photosystem performance. Beyond this DLI, these parameters and shoot biomass plateaued as the DLI increased. Moreover, treating seedlings with this optimal DLI of 39.6 mol m⁻² d⁻¹ (using 500 μmol m⁻² s⁻¹ light intensity and a 22 h d⁻¹ photoperiod) resulted in heading and flowering 5.9 and 7.5 days earlier after transplanting, respectively, than those under the lowest DLI (10.8 mol·m⁻²·d⁻¹). This study established a lighting strategy to produce high-quality seedlings and accelerate heading and flowering, thereby offering a valuable physiological framework for advancing speed-breeding systems in wheat.

Maize has a long generation cycle and sensitivity to photoperiod, which limit breeding efficiency. An LED plant factory with suitable light conditions provides a promising approach to overcoming challenges in speed breeding. This study optimized the LED light environment to enhance growth and tassel development in the maize inbred line from the V3 to V9 stages. Six lighting treatments were tested, combining three light intensities (800, 1200, and 1600 μmol m⁻² s⁻¹) and two photoperiods (10 h d⁻¹ and 12 h d⁻¹). Treatment with a light intensity of 1600 μmol m⁻² s⁻¹ and a photoperiod of 10 h d⁻¹ resulted in the highest shoot fresh weight (396.9 g per plant), shoot dry weight (42.4 g per plant), leaf area (51.3 dm² per plant), and stomatal length (34.6 μm), as well as improved photosystem performance. Furthermore, this treatment promoted tassel development, with the tassel length at the V9 stage being 45.8% longer than that under the treatment with a light intensity of 800 μmol m⁻² s⁻¹ and a photoperiod of 10 h d⁻¹. These findings establish an optimized lighting strategy that significantly enhances the growth and tassel development of maize inbred lines from the V3 to V9 stages, providing a suitable light environment for maize speed breeding in plant factory systems.

Flavonoid biosynthesis is proposed to play a critical role in floral organ development in Paeonia species. However, its specific involvement in stamen petalization remains unclear. This study identified and characterized 13 gene families related to flavonoid biosynthesis across four Paeonia species. Comparative and phylogenetic analysis revealed that most flavonoid biosynthesis-related genes experience lineage-specific expansion in P. ludlowii. Genes belonging to the same family were commonly clustered on chromosomes and displayed highly conserved domain and motif compositions. The cis-element analysis identified Cis-acting elements associated with light, hormonal, and stress responses, implicating their regulatory roles in flavonoid biosynthesis. To further investigate the role of these genes in stamen petalization of P. lactiflora, expression profiling analyses were performed on ‘Fen Yu Nu’ (normal stamens) and ‘Lian Tai’ (petaloid stamens) cultivars using transcriptomic data released previously. Three quercetin-related genes revealed distinct stage-specific patterns in ‘Fen Yu Nu’ and ‘Lian Tai’. Notably, PlaF3’H03 exhibited significant upregulation during petaloid stamen development in ‘Lian Tai’, suggesting its role in stamen transformation. Molecular docking identified PlaF3’H07 as a key enzyme with strong substrate-binding affinity (ΔG = −4.7 kcal/mol), supporting its catalytic function in quercetin synthesis. The expression pattern of key flavonoid biosynthetic genes was also confirmed across three developmental stages of floral buds by real-time quantitative PCR. This study provides insights into the genetic basis underlying stamen petalization in P. lactiflora and offers potential targets for genetic improvement of floral traits in Paeonia and other ornamental plants.