This study aimed to determine the effect of changes in light quality on the improvement of growth and bioactive compound synthesis in red-leaf lettuce ( Lactuca sativa L. ‘Sunmang’) grown in a plant factory with electrical lighting. Lettuce seedlings were subjected to 12 light treatments combining five lighting sources: red (R; 655 nm), blue (B; 456 nm), and different ratios of red and blue light combined with three light-emitting diodes [LEDs (R9B1, R8B2, and R6B4)]. Treatments were divided into control (continuous irradiation of each light source for 4 weeks), monochromatic (changing from R to B at 1, 2, or 3 weeks after the onset of the experiments), and combined (changing from R9B1 to R8B2 or R6B4 at 2 or 3 weeks after the onset of the experiments). Growth and photosynthetic rates of lettuce increased with increasing ratios of red light, whereas chlorophyll and antioxidant phenolic content decreased with increasing ratios of red light. Individual phenolic compounds, including chlorogenic, caffeic, chicoric, and ferulic acids, and kaempferol, showed a similar trend to that of total phenolics. Moreover, transcript levels of phenylalanine ammonia-lyase ( PAL ) and chalcone synthase ( CHS ) genes were rapidly upregulated by changing light quality from red to blue. Although the concentration of bioactive compounds in lettuce leaves enhanced with blue light, their contents per lettuce plant were more directly affected by red light, suggesting that biomass as well as bioactive compounds’ accumulation should be considered to enhance phytochemical production. In addition, results suggested that growth and antioxidant phenolic compound synthesis were more sensitive to monochromatic light than to combined light variations. In conclusion, the adjustment of light quality at a specific growth stage should be considered as a strategic tool for improving crop yield, nutritional quality, or both in a plant factory with electrical lighting.

Ethylene perception by ethylene receptors can be suppressed by ethylene antagonists, such as 1-methylcyclopropene (1-MCP). 1-MCP binds to ethylene receptors blocking ethylene binding, and thereby represses ethylene responses, including flower senescence and petal abscission. Despite its antagonistic propensity, plants treated with 1-MCP often regain sensitivity to ethylene, suggesting that ethylene receptors are synthesized de novo post-treatment. To investigate this observation, we determined the relationship between the mRNA levels of ethylene biosynthesis and ethylene receptor genes and the degree of ethylene sensitivity of carnation flowers after ethylene and 1-MCP treatments. Flowers treated with a single application of 1-MCP lost the inhibitory effect in ethylene production after 7d of the treatment. In contrast, multiple treatments with 1-MCP completely suppressed several ethylene biosynthesis genes and ethylene production throughout the experiment. Multiple 1-MCP treatments increased vase life by almost three-fold relative to control flowers. Eventually ethylene-independent browning and desiccation on the edges of petals contributed to loss of vase life. We observed that the transcript levels of the ethylene receptor genes, DcETR1 and DcERS1, decreased with flower development, but increased at the onset of floral senescence. Our results suggest that ethylene receptors are continually synthesized during later stages of floral development. While ethylene responsiveness is temporarily blocked by 1-MCP treatment, we predict that new receptors synthesized days after 1-MCP treatment can bind ethylene. This leads to the observed recovery of ethylene sensitivity in the flowers. In addition, we predict that the degradation of ethylene receptors that is stimulated by ethylene binding is prevented by successive treatments with 1-MCP prior to recovery of ethylene sensitivity. This study improves our understanding about the uses and effectiveness of 1-MCP and will facilitate the development and improvement of postharvest treatments for multiple crops

Botrytis cinerea (B. cinerea) is one of the necrotrophic pathogens resulting in the heaviest commercial losses in cut rose flowers, and the severity of gray mold disease partly depends on the presence of ethylene during the storage and transport. The effectiveness of nano silver (NS) and salicylic acid (SA) was assessed as a novel control agent in protecting the cut rose flowers against B. cinerea infection and ethylene damages. The efficacy of NS and SA was compared with an inoculated control (CON). A non-treated control (NT) was also used to evaluate the natural infection process. The results indicated that pretreatment with 20 mg L⁻¹ NS significantly reduced B. cinerea growth in rose petals during vase periods. NS effectively suppressed the mRNA levels of ethylene biosynthesis genes (RhACS2, RhACS4, and RhACO1) and the reduction in expression levels of ethylene receptor genes (RhETR1, RhETR2, and RhETR5) and the downstream regulator RhCTR2 in rose petals after B. cinerea inoculation. NS application also decreased the expression of the B. cinerea snod-prot-like 1 (Bcspl1) gene which acts as the virulence factor in cut roses. In NS flowers, the maximum quantum yield of PSII (F_v/F_m) value was higher and the leaf temperature was lower on day 1, suggesting that these factors can be used for detecting B. cinerea infection and water stress in cut rose flowers. Furthermore, NS improved water relations and extended the vase life of cut rose flowers by 3.3 d, compared with that of NT flowers. In contrast, SA had no inhibitive effects on both B. cinerea growth and ethylene response in cut roses. The findings from the present study highlight NS as a promising new candidate for preventing B. cinerea infection and ethylene damages and for improving the postharvest quality of cut roses exported overseas.