We explored the effects of different light intensities and photoperiods on the growth, nutritional quality and antioxidant properties of two Brassicaceae microgreens (cabbage Brassica oleracea L. and Chinese kale Brassica alboglabra Bailey). There were two experiments: (1) four photosynthetic photon flux densities (PPFD) of 30, 50, 70 or 90 μmoL·m−2·s−1 with red:blue:green = 1:1:1 light-emitting diodes (LEDs); (2) five photoperiods of 12, 14, 16, 18 or 20 h·d−1. With the increase of light intensity, the hypocotyl length of cabbage and Chinese kale microgreens shortened. PPFD of 90 μmol·m−2·s−1 was beneficial to improve the nutritional quality of cabbage microgreens, which had higher contents of chlorophyll, carotenoids, soluble sugar, soluble protein and vitamin C, as well as increased antioxidant capacity. The optimal PPFD for Chinese kale microgreens was 70 μmol·m−2·s−1. Increasing light intensity could increase the antioxidant capacity of cabbage and Chinese kale microgreens, while not significantly affecting glucosinolate (GS) content. The dry and fresh weight of cabbage and Chinese kale microgreens were maximized with a 14-h·d−1 photoperiod. The chlorophyll, carotenoid and soluble protein content in cabbage and Chinese kale microgreens were highest for a 16-h·d−1 photoperiod. The lowest total GS content was found in cabbage microgreens under a 12-h·d−1 photoperiod and in Chinese kale microgreens under 16-h·d−1 photoperiod. In conclusion, the photoperiod of 14~16 h·d−1, and 90 μmol·m−2·s−1 and 70 μmol·m−2·s−1 PPFD for cabbage and Chinese kale microgreens, respectively, were optimal for cultivation.
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.
The results in the process of the optimization of aseptic germination system of seeds in soybean were found as follows. Using the method of chlorine sterilization to sterilize soybean seeds for 2-4 hours were found to get the best results and found to be suitable for the growth of soybean seeds and obtainment of the best quality explants. Relative to other varieties, the soybean variety of Mao-Dou No. 5 was found to gain the best germination effects, and the localization way of seed inoculation and the light conditions had no significant effects on the germination of seeds of Glycine max.
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