Salt stress decreases seedling growth and development but increases quercetin and kaempferol content inApocynum venetum

Apocynum venetumL. is a traditional Chinese medicinal herb with great potential to treat angiocardiopathy. Its major medicinal constituents are flavonoids. However, the natural habitats ofA. venetumare 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 ofA. 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 mmNaCl). Furthermore, quercetin and kaempferol were significantly accumulated inA. venetumseedlings under salt stress, resulting in a balanced content and reduced FW. Moreover, the expression ofAvCHS,AvCHIandAvF3GTwas inhibited by salt stress; however,AvF3'H,AvF3HandAvFLS, 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 ofA. venetumin saline soils appeared to be feasible and improved the medicinal quality ofA. venetum(quercetin and kaempferol accumulation under salt stress), thus this species can effectively utilize saline soil resources.