Salt stress decreases seedling growth and development but increases quercetin and kaempferol content in Apocynum venetum.

Apocynum venetum L. is a traditional Chinese medicinal herb with great potential to treat angiocardiopathy. Its major medicinal constituents are flavonoids. However, the natural habitats of A. venetum are typically affected by salt stress, which can modify both biomass and accumulation of medicinal compounds. In this study, the effects of salt stress on growth and development of A. venetum, accumulation of flavonoids and expression patterns of genes involved in flavonoid biosynthesis were evaluated. In general, the growth and development of seedlings (seedling height, root length, leaf length, leaf width and seed germination) were inhibited by salt stress. Unlike typical halophytes, there was no optimal NaCl concentration range that promoted growth and development, but seedlings had an elevated DW/FW ratio under salt stress (induced by irrigation with 50, 100, 200 or 400 mm NaCl). Furthermore, quercetin and kaempferol were significantly accumulated in A. venetum seedlings under salt stress, resulting in a balanced content and reduced FW. Moreover, the expression of AvCHS, AvCHI and AvF3GT was inhibited by salt stress; however, AvF3'H, AvF3H and AvFLS, which are involved in the flavonol synthesis pathway, were up-regulated under salt stress, consistent with a decrease in total flavonoids and an increase of flavonols (quercetin and kaempferol). In summary, cultivation of A. venetum in saline soils appeared to be feasible and improved the medicinal quality of A. venetum (quercetin and kaempferol accumulation under salt stress), thus this species can effectively utilize saline soil resources.

Effects of nitrogen supply on flavonol glycoside biosynthesis and accumulation in tea leaves (Camellia sinensis).

Widely distributed in tea plants, the flavonoid flavonol and its glycosylated derivatives have important roles in determining tea quality. However, the biosynthesis and accumulation of these compounds has not been fully studied, especially in response to nitrogen (N) supply. In the present study, 'Longjing 43' potted tea seedlings were subjected to N deficiency (0g/pot), normal N (4g/pot) or excess N (16g/pot). Quantitative analyses using Ultra Performance Liquid Chromatography-Triple Quadrupole Mass Spectrometry (UPLC-QqQ-MS/MS) revealed that most flavonol glycosides (e.g., Quercetin-3-glucoside, Kaempferol-3-rgalactoside and Kaempferol-3-glucosyl-rhamnsoyl-glucoside) accumulated to the highest levels when treated with normal N. Results from metabolomics using Gas Chromatography-Mass Spectrometer (GC-MS) suggested that the levels of carbohydrate substrates of flavonol glycosides (e.g., sucrose, sucrose-6-phosphate, D-fructose 1,6-bisphosphate and glucose-1-phosphate) were positively correlated with flavonol glycoside content in response to N availability. Furthermore, Quantitative Real-time PCR analysis of 28 genes confirmed that genes related to flavonoid (e.g., flavonol synthase 1, flavonol 3-O-galactosyltransferase) and carbohydrate (e.g., sucrose phosphate synthase, sucrose synthase and glucokinase) metabolism have important roles in regulating the biosynthesis and accumulation of flavonol glycosides. Collectively, our results suggest that normal N levels promote the biosynthesis of flavonol glycosides through gene regulation and the accumulation of substrate carbohydrates, while abnormal N availability has inhibitory effects, especially excess N.

De novo biosynthesis of myricetin, kaempferol and quercetin in Streptomyces albus and Streptomyces coelicolor.

Flavonols are a flavonoid subfamily widely distributed in plants, including several ones of great importance in human and animal diet (apple, tomato, broccoli, onion, beans, tea). These polyphenolic nutraceuticals exert potent antimicrobial (membrane potential disruptors), antioxidant (free-radical scavengers), pharmacokinetic (CYP450 modulators), anti-inflammatory (lipoxygenase inhibitors), antiangiogenic (VEGF inhibitors) and antitumor (cyclin inhibitors) activities. Biotechnological production of these nutraceuticals, for example via heterologous biosynthesis in industrial actinomycetes, is favored since in plants these polyphenols appear as inactive glycosylated derivatives, in low concentrations or as part of complex mixtures with other polyphenolic compounds. In this work, we describe the de novo biosynthesis of three important flavonols, myricetin, kaempferol and quercetin, in the industrially relevant actinomycetes Streptomyces coelicolor and S. albus. De novo biosynthesis of kaempferol, myricetin and quercetin in actinomycetes has not been described before.