Abstract
To determine the response of Chinese kale (Brassica alboglabra) sprouts to photoperiods under different light sources, we used four photoperiods (0-h light/24-h dark, 8-h light/16-h dark, 12-h light/12-h dark, and 16-h light/8-h dark) to investigate their sprout growth and secondary metabolite glucosinolates (GSs) accumulation under white or combined red-and-blue (RB) light sources. We found that the 16-h light condition under RB light produced plants with the greatest dry matter. Sprouts grown under 16-h RB light condition achieved greater length than those under white light. To investigate the role of RB light in plant growth and GS accumulation, we applied RB light sources with different RB ratios (0:10, 2:8, 5:5, 8:2, and 10:0) to cultivate sprouts. The results showed that significant differential accumulation of GSs existed between sprouts grown under blue (RB, 0:10) and red (RB, 10:0) light; there was greater GS content under blue light. The underlying mechanism of differential GS content in sprouts under red or blue light condition was studied using RNA sequencing technique. Interestingly, abundant GS biosynthetic gene transcripts were observed in sprouts grown under red light compared with under blue light. The expression of β-glucosidase family homolog genes related to GS degradation differed under red and blue light conditions, among those TGG4 homolog was detected with higher expression under red light than with blue light. Taking into consideration, the lower GS accumulation in sprouts under red rather than blue light, we conclude that the degradation of GSs may play a key role in sprouts GS homeostasis.
Highlights
Chinese kale sprouts are widely regarded as a healthy vegetable through their substantial nutritional components and strong antioxidant ability
Under the 18-h light condition, both types of sprouts grew with shorter hypocotyls and wider cotyledons irrespective of whether a W or combined RB light source was used (Figure 1A)
Under a combined RB light (8:2) source, the plant height was much greater, and the cotyledon length was significantly shorter in 9-day-old sprouts than in those grown under W light (Figures 1B,C)
Summary
Chinese kale sprouts are widely regarded as a healthy vegetable through their substantial nutritional components and strong antioxidant ability. Originating in China, Chinese kale sprouts contain abundant glucosinolates (GSs), vitamin C, and polyphenols. Practices such as adding sugar, applying different light, adding NaCl, and using hormone treatments have been used to promote the quality of kale sprout production (Guo et al, 2011, 2013; Qian et al, 2016). Blue light (470 nm) exposure has been found to accelerate aliphatic GS levels, while decreased indolic GS accumulation in Cardamine fauriei (Abe et al, 2015). Application of blue light at 450 or 470 nm increased the total GS content in turnips (Antonious et al, 1996) and broccoli (Kopsell and Sams, 2013), respectively, whereas red light (650 nm) treatment increased the accumulation of aliphatic GSs in watercress (Nasturtium officinale) (Engelen-Eigles et al, 2006)
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