Multiple mechanism confers natural tolerance of three lilyturf species to glyphosate.

MAIN CONCLUSION: A combination of unique EPSPS structure and increased gene copy number and expression contribute to natural glyphosate tolerance in three lilyturf species. A few plants are naturally tolerant to glyphosate, the most widely used non-selective herbicide worldwide. Here, the basis for natural tolerance to glyphosate in three lilyturf species, Ophiopogon japonicus (OJ), Liriope spicata (LS), and Liriope platyphylla (LP), is characterized. These species tolerate glyphosate at about five times the commercially recommended field dose. They share three unique amino acids in their 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) that affect glyphosate binding. These correspond to Asp71Met, Ala112Ile, and Val201Met amino acid variations compared to 231 other published plant EPSPS amino acid sequences. There was also a common deletion at 91 of a highly conserved glutamic acid. Glyphosate-treated lilyturf plants accumulated little shikimic acid but had significantly higher levels of EPSPS mRNA than initially expressed in the control. The IC50 of LsEPSPS was 14.0 µM compared to the 5.1 µM of Arabidopsis thaliana. The higher K m and K i values of LsEPSPS kinetics showed that LsEPSPS had lower substrate binding affinity to glyphosate. Overexpression of LsEPSPS in the recombinant E. coli BL21 (DE3) strain enhanced its tolerance to glyphosate. Both OJ and LS had two copies of the EPSPS gene, while LP had three copies. Therefore, a combination of unique EPSPS structure and increased gene copy number and expression contribute to natural glyphosate tolerance in the three lilyturf species.

Cause and control of Radix Ophiopogonis browning during storage.

In the storage of Radix Ophiopogonis, browning often happens to cause potential risk with regard to safety. Previously few reports investigate the browning of Radix Ophiopogonis. In this research, the causes and mechanisms of the browning of Radix Ophiopogonis were preliminarily elucidated. Content determination by high-performance liquid chromatography (HPLC) and spectrophotometry, enzyme activity determination by colorimetry, and morphological observation by electron microscopy were performed in the present study. Uniform design and three-dimensional response surfaces were applied to investigate the relationship between browning and storage factors. The cortex cell wall of browned Radix Ophiopogonis was ruptured. Compared with the normal Radix Ophiopogonis, cellulase and polyphenol oxidase enzymes were activated, the levels of 5-hydroxymethylfurfural (5-HMF), total sugars, and reducing sugars were increased, while the levels of polysaccharides and methylophiopogonanone A were decreased in browned Radix Ophiopogonis. The relationship between the storage factors and degree of browning (Y) could be described by following correlation equation: Y = - 0.625 4 + 0.020 84 × X3 + 0.001 514 × X1 × X2 - 0.000 964 4 × X2 × X3. Accompanied with browning under storage conditions, the chemical composition of Radix Ophiopogonis was altered. Following the activation of cellulase, the rupture of the cortex cell wall and the outflow of cell substances flowed out, which caused the Radix Ophiopogonis tissue to become soft and sticky. The main causes of the browning were the production of 5-HMF, the activation of polyphenol oxidase, Maillard reactions and enzymatic browning. Browning could be effectively prevented when the air relative humidity (HR), temperature, and moisture content were under 25% RH, 12 °C and 18%, respectively.