Recent Advances in Bioactive Compounds, Health Functions, and Safety Concerns of Onion (Allium cepa L.).

Onion (Allium cepa L.) is a common vegetable, widely consumed all over the world. Onion contains diverse phytochemicals, including organosulfur compounds, phenolic compounds, polysaccharides, and saponins. The phenolic and sulfur-containing compounds, including onionin A, cysteine sulfoxides, quercetin, and quercetin glucosides, are the major bioactive constituents of onion. Accumulated studies have revealed that onion and its bioactive compounds possess various health functions, such as antioxidant, antimicrobial, anti-inflammatory, anti-obesity, anti-diabetic, anticancer, cardiovascular protective, neuroprotective, hepatorenal protective, respiratory protective, digestive system protective, reproductive protective, and immunomodulatory properties. Herein, the main bioactive compounds in onion are summarized, followed by intensively discussing its major health functions as well as relevant molecular mechanisms. Moreover, the potential safety concerns about onion contamination and the ways to mitigate these issues are also discussed. We hope that this paper can attract broader attention to onion and its bioactive compounds, which are promising ingredients in the development of functional foods and nutraceuticals for preventing and managing certain chronic diseases.

The ameliorative effect of silicon on soybean seedlings grown in potassium-deficient medium.

BACKGROUND AND AIMS: Crop yield and nutritional quality are significantly reduced when potassium (K) in soil is deficient. As a beneficial element for plants, silicon (Si) is effective in alleviating the toxic effects of mineral nutrients. However, the roles played by Si in mediating deficiency in essential mineral nutrients in general and K in particular have not been investigated. METHODS: To evaluate the role of Si in K deficiency-induced inhibition of growth of soybean (Glycine max) seedlings, the effects of K deficiency on shoot and root growth, hydrogen peroxide accumulation, K contents, lipid peroxidation and activities of antioxidant enzymes in the absence and presence of 2 mM sodium silicate (Na(2)SiO(3)) were investigated. KEY RESULTS: Both shoot and root biomass of soybean seedlings were markedly reduced when grown in K-deficient medium (1 mM K) compared with those grown in K-sufficient medium (5 mM). Addition of Na(2)SiO(3) significantly ameliorated the K deficiency-induced reductions in shoot and root growth. Sodium silicate enhanced K concentrations in leaf, stem and root of K-deficient seedlings by 105.4, 83.4 and 58.8 %, respectively. Hydrogen peroxide (H(2)O(2)) and malondialdehyde (MDA) contents in soybean seedlings were increased by 25 and 97 %, respectively, when exposed to K-deficient medium. These increases in accumulation of H(2)O(2) and MDA were removed by addition of Na(2)SiO(3). Addition of Na(2)SiO(3) reduced the K deficiency-induced increases in activities of superoxide dismutase, catalase and peroxidase. CONCLUSIONS: Application of Si to soybean seedlings grown in K-deficient medium markedly enhanced K use efficiency. Therefore, Si not only increases tolerance to nutrient toxicity, but also ameliorates symptoms associated with deficiency in essential nutrients in plants.