Phytotoxic mechanism of allelochemical liquiritin on root growth of lettuce seedlings.

As the main active ingredient of the traditional Chinese medicine Glycyrrhiza uralensis Fisch, liquiritin has multiple biological activities, including anti-inflammatory, antihepatotoxicity, immune regulation, anti-virus and anti-cancer. In addition, liquiritin has been recognized as an allelochemical that displays markedly inhibitory effects on the growth of target plants, G. uralensis and lettuce. However, its phytotoxic mechanism remains unknown. In the present study, the mode of action of liquiritin against root growth of lettuce seedling was researched. After treatments with liquiritin, the cell division in root tips of lettuce seedlings was partly arrested, and the cell viability and root vitality were obviously lost. At the same time, overproduction of reactive oxygen species (ROS), malondialdehyde (MDA) and proline (Pro) in lettuce seedlings were induced by liquiritin. The results indicated that the phytotoxic effects of liquiritin was probably dependent on the induction of ROS overproduction, resulting in membrane lipids peroxidation following with cell death and mitosis process disorder.

Efficient expression of novel glutamate decarboxylases and high level production of γ-aminobutyric acid catalyzed by engineered Escherichia coli.

Glutamate decarboxylase (GAD) has the potential of converting L-glutamate to gamma-aminobutyric acid (GABA), which is an important non-proteinogenic amino acid that has a potential use as food additive or dietary supplement for its physiological functions. A novel pyridoxal 5'-phosphate (PLP)-dependent glutamate decarboxylase (LsGAD) was cloned from GRAS (generally recognized as safe) Lactobacillus senmaizukei by genome mining and efficiently expressed in Escherichia coli BL21. The LsGAD displayed excellent temperature property, pH property and kinetic parameters compared with the probe LbGAD and the other GADs. By increasing the copy number of the LsGAD encoding gene, the expression level of LsGAD and the biosynthesis yield of GABA were increased, which was near to 2 times of that was expressed in single copy. These results established a solid foundation for increasing the added value of L-glutamate and the biosynthesis of GABA.

[Screening for peptides of anti-rotavirus by phage-displayed technique].

In this study, a 15-mer phage display peptide library was employed to pan against human rotavirus immobilized on solid phase. 4 different peptides were selected and could bind with rotavirus particles specifically. Plaque reduction neutralization test and MTT analysis results indicated that 3 of the peptides can inhibit rotavirus infecting in vitro. A peptide which sequence is QSNPIHIITNTRNHP showed the best efficiency--93% neutralization infectivity. Two other peptides, A and B, showed 40% and 50% neutralization infectivity respectively. Amino sequence analysis results indicate the 3 peptides containing 2 conserved motifs: SNPIHII and NIP. No putative trypsin hydrolysis site was found in C peptide, however, 4 and 3 potential sites were found in A and B peptides respectively. Using trypsin inhibitor, both A and B peptides showed the similar antiviral effect as that of C peptide. It suggests that the intactness of the 2 conserved motifs play an important role in counteracting virus infection. According to the results of this study, peptide C is hopeful to be exploited as an antiviral peptide drug.