Abstract
Chinese kale baby leaves were hydroponically cultured under the basal light (Red: white LEDs = 2:3 at PPFD of 250 μmol·m−2·s−1) with different supplemental lighting, including individual ultraviolet-A (UV-A, 380 ± 10 nm, 20 μmol·m−2·s−1), far-red (FR, 735 ± 10 nm, 30 μmol·m−2·s−1) light, and their combination (UF) radiation in an artificial light plant factory. Effects of supplemental light qualities on morphology and physiology as well as health-promoting compounds of Chinese kale baby leaves were investigated. Application of UV-A and FR presented a positive effect on biomass, with a pronounced increase in petiole length, stem diameter, main stem length, and leaf area. Notably, plants under UF grew more vigorously than under other treatments. Higher levels of FRAP, vitamin C, total phenolic, and flavonoid were observed in plants under UV-A, while no striking changes or a decreasing trend recorded under FR and UF. Moreover, UV-A enhanced the glucosinolates (GLs) accumulation in Chinese kale baby leaves by increasing the predominant GLs (glucoraphanin and glucobrassicin) contents. RT-qPCR results indicated that UV-A upregulated the gene expressions of transcription factors and core structure genes related to GLs biosynthesis. However, downregulated or unchanged gene expressions of GLs biosynthesis-related genes in Chinese kale baby leaves were observed in FR and UF. Therefore, UV-A was benefited for the production of functional substances, while FR was conducive to a significant increase in crop yield. The combination of UV-A and FR, as a balance between yield and production of secondary metabolite, provided a new perspective for the application of artificial light in horticultural crop production.
Highlights
Light provides energy for plant photosynthetic, but it is the most indispensable environmental signal to trigger an ensemble of signal-transducing photoreceptors that regulate plant growth, development, and metabolism (Karpinski et al, 2013)
Effects of supplemental UV-A lighting on Chinese kale baby leaves growth depended on the growth stage of plants, where UV-A presented a negative effect on biomass at the early vegetative stage while enhanced the yield at the later stage
The morphological, physiological, and biochemical characteristics of Chinese kale baby leaves were altered by UV-A, FR, and UV-A + FR treatment (UF) radiation
Summary
Light provides energy for plant photosynthetic, but it is the most indispensable environmental signal to trigger an ensemble of signal-transducing photoreceptors that regulate plant growth, development, and metabolism (Karpinski et al, 2013). Health-Promoting; Chinese Kale Baby-Leaf; UV-A; Far-Red Light photoreceptors or players, such as HY5, COP1, PIFs (Saijo et al, 2003), regulating plant morphology and a metabolite across an entire plant life cycle. Ultraviolet-A (UV-A) light and far-red (FR) light, kinds of invisible lights, have created new opportunities to alter plant morphological and physiological properties, which depend on their wavelengths, intensities, and irradiation time (Fukuyama et al, 2017; Li et al, 2020a; Zhang et al, 2020; He et al, 2021)
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