Transcriptome sequencing revealed the influence of blue light on the expression levels of light-stress response genes in Centella asiatica

The influence of prolonged but low intensity blue light on the physiological properties of root tubers and the accumulation of flavonoids in Tetrastigma hemsleyanum Diels et Gilg

Tetrastigma hemsleyanum Diel et Gilg is a perennial herbaceous plant native to subtropical China with multiple medicinal applications. Supplementing with low-density blue light (BL) for 45 days (3 h/day) can not only significantly increase the yields of root tubers but also significantly increase the flavonoid content and its antioxidant activity. The chlorophyll content in the leaves of T. hemsleyanum significantly decreased, but the photosynthetic efficiency significantly increased after reaching the light saturation point. The production rate of superoxide anion radical in the leaves reached the highest peak after 1.5 h in BL and decreased at 3 h. The H2O2 content in the leaves decreased significantly, while the H2O2 content in the root tubers increased significantly at 3 h in BL. The objective of this research was to determine how the scavenging system, including antioxidant enzymes, antioxidants, and flavonoids respond to the oxidative stress induced by BL in root tubers. After exposure to BL, significant differences in the activity of APX and SOD were observed in the leaves and tubers within 3 h. By analyzing the upregulated flavonoids metabolites and key genes in metabolic pathways through the combined analysis of the flavonoid metabolic group and transcriptome in the root tubers, the upregulated accumulation of flavanols was found to be the main reason for the improvement in the antioxidant properties of flavonoids.

Harnessing postharvest light emitting diode (LED) technology of Centella asiatica (L.) Urb. to improve centelloside content by up-regulating gene expressions in the triterpenoid pathway

Centella asiatica (L.) Urb. has wound healing, anti-inflammatory, cognitive improvement, and neuroprotective properties which have been attributed to its centelloside content. However, the quantities of these bioactive compounds are limited and vary due to genetic and environmental factors. Light qualities are known to enhance the production of secondary metabolites in several plant species, both preharvest and postharvest. In this study, fresh leaves of C. asiatica were subjected to different light emitting diode (LED) quality including white, dark, red, blue, and green to assess centelloside content, phytochemical constituents, and transcription level expression of triterpenoid biosynthesis genes. Results showed that white and blue LEDs significantly increased centelloside content in C. asiatica leaves at 3 days postharvest (dph) by 73 % over the control group at 0 dph. Blue LEDs stimulated the expression of triterpenoid biosynthesis genes including C. asiatica squalene synthase (CaSQS), C. asiatica β-amyrin synthase (CabAS), and C. asiatica UDP gluclosyltransferase-73AH1 (CaUGT73AH1; CaUGT), while different LED conditions gave diverse results. Red LED treatment triggered higher total flavonoid content (TFC) and total triterpenoid content (TTC) while white LEDs enhanced total triterpenoid content (TTC). Taken together, our findings suggest that postharvest under blue LEDs is a great approach to increase centelloside production of C. asiatica through gene up-regulation in triterpenoid pathway. Therefore, postharvest technology by LEDs serves as an effective tool for improving raw material quality for medicinal plant industries.

Effect of light quality on polyphenol biosynthesis in three varieties of mung bean sprouts with different color seed coats

We investigated the mechanism of the effect of different light qualities on the synthesis and regulation of mung bean sprouts. Light quality acts as a signal molecule, strongly enhancing polyphenol biosynthesis in sprouts. Mung bean (Vigna radiata) sprouts are a popular sprouting vegetable all over the world and are an excellent source of polyphenols with high antioxidant activity. This study investigated the effects of light qualities on the kinetic changes and metabolic regulation mechanism of light signal-mediating polyphenols in three mung bean sprout cultivars. Experimental results showed that three light qualities significantly enhanced the contents of caffeic acid, rutin, vitexin, genistin and delphinidin 3-glucoside. Interestingly, ferulic acid and vitexin responded selectively to blue light and red light, severally. Most genes involved in polyphenol biosynthesis were activated under different light quality conditions, resulting in an overaccumulation of phenylpropanoids. Pearson correlation analysis showed that PAL, F3H, F3'H and F3'5'H expression correlated highly with rutin, whereas ANS expression paralleled anthocyanin biosynthesis. Moreover, MYB111, MYB3, MYB4, MYB1 and MYC2 were critical regulators of polyphenol biosynthesis in mung bean sprouts. These changes were likely due to the changes in the expression of the photoreceptor genes CRY-D, PHOT2, PHYE and light response genes (PIF3 and HY5). Our results provide insights into polyphenol biosynthesis in sprouts and microgreens.

Colored LED Lights: Use One Color Alone or with Others for Growth in Hedyotis corymbosa In Vitro?

In recent years, light-emitting diode (LED) technology has been applied to improve crop production and induce targeted biochemical or physiological responses in plants. This study investigated the effect of different ratios of blue 450 nm and red 660 nm LEDs on the overall plant growth, photosynthetic characteristics, and total triterpenoid production in the leaves of Hedyotis corymbosa in vitro plants. The results showed that a high proportion of blue LED lights had a positive effect on enhancing photosynthesis and the overall biomass. In addition, blue LED lights were shown to be more effective in controlling the production of the total triterpenoid content compared with the red LED lights. Moreover, it was also found that plants grown under a high proportion of red LEDs exhibited reduced photosynthetic properties and even induced damage to the photosynthetic apparatus, which indicated that the blue or red LED lights played contrary roles in Hedyotis corymbosa.