Optimization Of Melatonin Nano Delivery System And Mechanisms Underlying Its Improved Saline-alkali Tolerance In Rapeseed

Soil salinization is widely distributed globally and has rapidly expanded in recent years.The situation of salinization and alkalization in China is not optimistic,as the available arable land area is decreasing year by year,which seriously restricts the development speed of agriculture.In the early 21st century,the rapid development of nanobiotechnology sparked a wave in the agricultural field,with enormous potential for improving plant resistance to stress.Zein nanoparticles（NZ）,as a new type of nanomaterials,have excellent drug loading performance and excellent biological effects.This project uses NZ nanoparticles to load phytohormone Melatonin（MT）to generate nanocomposites（NZ-MT）.Zhongshuang 11 in Brassica napus is used as the experimental object to explore the mechanism of NZ nanoparticles for improving the salt tolerance of rapeseed seeds and NZ-MT nanomaterial for improving the alkali resistance of rapeseed seedlings.The research results show that NZ nanoparticles can indeed improve the salt tolerance of rapeseed seeds.The application of NZ-MT nanomaterials on the leaves can improve the growth status of rapeseed seedlings under alkali stress,which is of great significance for the rational and correct use of plant hormones to enhance the plant’s ability to withstand salt and alkali stress.The main results of the study are as follows:（1）MSNs and NZ nanoparticles were synthesized,and the biological effects of the two nanomaterials were compared.It was confirmed that the initiation of NZ nanoparticles could significantly improve the growth status of rapeseed seeds under 250 m M Na Cl salt stress,such as germination rate and biomass.Compared with the control group,0.308mg/m L of NZ nanomaterial significantly increased the germination rate,peroxidase（POD）,and catalase（CAT）activities of rapeseed seeds under salt stress,reduced the content of hydrogen peroxide（H₂O₂）and superoxide anion(O₂^·-)in the seedlings,and alleviated the oxidative damage caused by salt stress.Soluble proteins and other osmotic regulating substances increase,resulting in a lower water potential.The reduction of malondialdehyde（MDA）protects the integrity of the membrane system and ensures its normal life activities.（2）The measurement results of the water absorption and related gene expression of rapeseed seeds during the NZ nanoparticle initiation process showed that the water absorption of rapeseed seeds during the initiation process was significantly higher than that of the control group.This was consistent with the upregulation of the TIP 1 gene in the seeds,and the upregulation of the expression of Mn-SOD and CAT genes also enhanced the salt tolerance of the seeds.In summary,NZ nanoparticles had excellent biological effects and could significantly enhance the resistance of rapeseed seeds to salt stress after initiation.（3）The use of NZ-MT nanoparticles on the leaves of rapeseed seedlings significantly improved their growth under 160 m M Na HCO₃ alkali stress.After foliar application of NZ-MT,the activities of peroxidase（POD）,catalase（CAT）and superoxide dismutase（SOD）in the leaves of rape seedlings were increased,and the content of active oxygen species(H₂O₂ and O₂^·-)was reduced.The results of ROS tissue staining and confocal imaging also confirmed that there were fewer ROS in the leaves of rapeseed after NZ-MT treatment,which alleviated the oxidative stress response of rapeseed seedlings under alkali stress.（4）After NZ-MT treatment of rapeseed seedlings under alkaline stress,there was a significant increase in osmoregulation substances such as proline in their leaves,a decrease in malondialdehyde（MDA）content,and a reduction in electrolyte leakage,all of which confirmed the integrity of the membrane system of rapeseed leaves treated with NZ-MT.The PI staining results also confirmed that the membrane structure of rapeseed leaves treated with NZ-MT was more complete.NZ-MT nanomaterials were used to treat rapeseed seedlings,it can significantly improve its resistance under alkaline stress.Overall,our results showed that NZ can be used as an effective delivery tool to deliver hormones to plants to improve its tolerance to stresses such as salt-alkali stress.