| Chemical weed control is an important symbol of modernization in agriculture, is the urgent need to ensure food security. However, the herbicide is a "double-edged sword"; they could easily lead to crop injury owing to misuse or adverse weather conditions. Applying safeners is the most direct and effective way to solve this issue. However, currently, all commercialized safeners are chemical synthesis, there are few commercial safeners for wet-sown rice, and chemically synthesized safeners inevitably bring out new latent environmental pollution risks. Therefore, to seek new eco-friendly and efficient safeners has become a priority in the field of herbicides, plant-derived agents are safe possess these qualities. Last two decades has witnessed our progress of exploring botanical original safeners, and the latest discovery that pepper extract can make rice seedlings from the phytotoxicity of metolachlor (Met). Therefore, the author has launched a series of related work to clarify the new features from a new perspective sanshools and its mechanism of safening rice seedlings, which will be of very important theoretical significance and potential application value for finding out the highly efficient and low toxic or non-toxic herbicides and botanical safeners.1Preparation and analysis of sanshoolsThe ingredients (namely sanshools) that produce tingling were obtained by CO2supercritical fluid extraction from pepper fruit with the extraction efficiency of10.87%. Then the pepper oil resin was refined with petroleum ether. After analysis by HPLC, it showed that there were three components, two of which was over90%. Further identified by UPLC-MS, including various isomers, eleven sanshools were detected:hydroxy-α/β/ε-sanshool (70.06%), γ-sanshool (10.54%), hydroxy-y-sanshool (9.60%),2’,3’-dihydroxy-α/β-sanshool (4.65%), α/β/ε-sanshool (2.13%) and dehydro-γ-sanshool (3.02%).2Safening effect of sanshools and pepper oil resin on rice treated with metolachlorTo study the detoxifying effect of sanshools on rice seedlings, the rice seedlings were treated with Met of0.25μM and0.31mg-kg’1in agar and soil potted modes, respectively, in the basis of their IC50s. The recovery effect of plant height indicted that the best safening effect of sanshools on rice seedlings in agar and soil potted modes were1.0mg·L-1and5.0mg·kg-1, respectively.For field plot experiment, the rice was treated3ds after transplanting. Rice plant height and tiller number were surveyed in given plant and place four times within one month after the treatment; Plant height, major economic traits at harvest and rice quality full-term testing were investigated. The results in the early vegetative growth stage suggested that Met significantly impact on plant height and tiller number of rice seedlings, but as time goes on, there are signs of self-recovery; and the rice seedlings treated with pepper oil resin were being well protected, especially in the higher dose treatments. The results of main economic traits indicated that Met mainly reduced the available panicles of rice, seed setting rates and actual yield, the safened rice by pepper oleoresin were suffered less impact, and there was no significant difference compared with the control; However, Met possessed little influence on plant height,1000-grain weight, ear length and quality of rice full-term, are not significantly affected. So, Met caused rice to recessive injury, although not including rice quality, but eventually led to decline the yield.3Effect of sanshools on the rice seedling and pepper oil resin on the efficiency of weed-control by MetResults of seed germination test showed that the plantules were significantly inhibited in the treatments with sanshools of1.5mg·L-1and0.15mg·L-1, their plantule length were36.13%and56.44%of the non-treated, respectively; the radicles were extremely significantly inhibited in treatment of1.5mg·L-1, followed by the0.15mg·L-1and0.015mg·L-1, there was significant difference between them, the average length of radicle in the former (1.5mg·L-1) was44.56%of the non-treated, while the latter were69.01%and79.63%of the non-treated, respectively, and there was a significant difference between the other treatments and the non-treated. For the effect of sanshools on rice seedling growth, the results showed that, the rice seedling height was significantly inhibited in treatments with sanshools of1.5mg·L-1, there was a significant difference compared to the other treatments; there were no significant differences between the other treatments and the non-treated. The effect of sanshools on rice roots was more complex, rice roots were significant inhibited in the treated with sanshools of1.5mg·L-1, however, were significantly promoted in the treated of0.015mg·L-For the effect of sanshools on the efficiency weed-control of metolachlor, results of indoor test and field experiment showed that sanshools do not affect the effectiveness of the prevention and control of barnyard grass.4Detoxifying mechanism of sanshools on rice seedlingThe Met-treated (0.25μM) rice seedlings, which were56.0%,66.0%, and57.0%of the non-treated control in shoot height, root length, and fresh biomass, respectively, were recovered by S to93.1%,97.6%, and94.8%, respectively. The emergence rate was enhanced to over80%in the Met+S treatment, whereas it was below60%in the Met treatment. This Met+S mixture elevated the rice-seedling root activity to higher than87.0%of the value for the non-treated control. The activity of glutathione transferases in the combined treatments approximately doubles that of the Met treatment and quadruples that of the non-treated controls. This effect was positively correlated with the induced expression of OsGSTU3. Our results suggest that S may represent a new group of safeners and enable the possibility of using these compounds for improving plant production or protecting rice from the phytotoxicity of metolachlor.In summary, sanshools were prepared by CO2supercritical extraction from the pepper fruit with the extraction efficiency of more than1%; Through laboratory and field tests, sanshools were proved that they could well alleviate the injury from metolachlor in rice, which by activating GSTs encoded genes, resulted in enhancing the metabolism of metolachlor, in which, OsGSTU3played a more vital role. This study will be of very important theoretical significance and potential application value for illuminating the mechanism of safeners and finding out the highly efficient and low toxic or non-toxic herbicides and botanical safeners. |
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