Rhodopseudomonas palustris strain PS3, a phototrophic bacterium, was originally isolated from a paddy field located in Taipei city, Taiwan, and showed positive effects on the growth of leafy vegetables. The aim of this study was to clarify the mechanism of the beneficial effects exerted by PS3 on plants. An ineffective R. palustris strain, YSC3, isolated from a paddy field located in Yilan County, was used as the negative control for comparative analyses. We cultivated non-heading Chinese cabbage (Brassica rapa var. chinensis) in 1/2 strength Hoagland hydroponic solution, in which nitrate is the main nitrogen source. We evaluated various plant physiological responses to inoculation with different bacterial inoculants. The N use efficiency (NUE) of PS3-inoculated plants was dramatically higher than that of YSC3-inoculated plants. The nitrate uptake efficiency (NUpE) was significantly elevated in plants treated with PS3; however, no excess nitrate accumulation was observed in leaves. We also noticed that the endogenous indole-3-acetic acid (IAA) levels as well as the cell division rate in the leaves of PS3-inoculated plants were significantly higher than those in the leaves of YSC3-inoculated plants. We examined the bacterial transcription of some genes during root colonization, and found that the expression level of IAA synthesis related gene MAO was almost the same between these two strains. It suggests that the elevated endogenous IAA in the PS3-inoculated plants was not directly derived from the exogenous IAA produced by this bacterium. Taken together, we deduced that PS3 inoculation could promote plant growth by enhancing nitrate uptake and stimulating the accumulation of endogenous auxin in young expanding leaves to increase the proliferation of leaf cells during leaf development.

No abstract

No abstract

No abstract

Polyphenols are important secondary metabolites from the edible and medicinal mushroom Inonotus obliquus. Both the rarity of I. obliquus fruit body and the low efficiency of current method of submerged fermentation lead to a low yield of polyphenols. This study was aimed to determine the effect of applying stimulatory agents to liquid cultured I. obliquus on the simultaneous accumulation of exo-polyphenols (EPC) and endo-polyphenols (IPC). Linoleic acid was the most effective out of the 17 tested stimulatory agents, the majority of which increased the EPC and IPC production. The result was totally different from the stimulatory effect of Tween 80 for polysaccharide production in previous studies. The addition of 1.0 g/L linoleic acid on day 0 resulted in 7-, 14-, and 10-fold of increase (p < 0.05) in the production of EPC extracted by ethyl acetate (EA-EPC), EPC extracted by n-butyl alcohol (NB-EPC), and IPC, and significantly increased the production of ferulic acid, gallic acid, epicatechin-3-gallate (ECG), epigallocatechin-3-gallate (EGCG), phelligridin G, inoscavin B, and davallialactone. The EA-EPC, BA-EPC, and IPC from the linoleic acid-containing medium had significantly (p < 0.05) stronger scavenging activity against 2,2-diphenyl-1-picrylhydrazyl radicals (DPPH), which was attributed to the higher content of these bioactive polyphenols.