| 其他摘要 | Drought has become an important abiotic stress affecting the growth and yield of crops. Wheat is one of the most important food crops in China and the world, and about 70% of wheat is grown in arid and semi-arid areas. The most effective and simple way to improve the drought resistance of crops is to enhance the drought resistance through the application of exogenous substances, so it is urgent to develop safe and efficient drought inhibitors. Chitosan can alleviate the damage caused by abiotic adversities such as drought and salt, and induce broad-spectrum resistance in plants, and has the advantages of being non-toxic and degradable. As an exogenous substance, chitosan has a promising application in agricultural production.
Chitosan is often modified by functionalization to confer different functional properties or to have new biological activities. Aminobutyric acid is a small-molecule non-protein amino acid that has a role in enhancing plant stress resistance and plays an important role in plant response to adversity stress. Based on the idea of active structure splicing, this thesis prepared novel chitosan-aminobutyric acid derivatives by modifying chitosan with two configurations of β and γ aminobutyric acid. The drought tolerance of wheat seedlings under drought stress was also investigated. Metabolomics technology was used to study the metabolic regulation of wheat seedlings affected by derivatives and to preliminarily explore the mechanism of drought tolerance induced by derivatives on wheat seedlings. The main research results of this thesis were as follows：
1.A total of six new chitosan-aminobutyric acid derivatives of two types were synthesized by amidation reaction of chitosan amino group with carboxyl group of aminobutyric acid, and the structures of the derivatives were characterized by carbon-13 nuclear magnetic resonance spectroscopy（13C-NMR）, proton-1 nuclear magnetic resonance spectroscopy（1H-NMR）and Fourier transform infrared spectroscopy（FT-IR） with substitution degree of more than 15%.
2.Both drought models, soil-potted drought and artificial drought, significantly inhibited the growth and development of wheat seedlings, significantly decreased seedling height, seedling fresh weight and seedling dry weight. Compared with the drought treatment alone, the derivative treatment significantly reduced malondialdehyde content and electrolyte leakage rate, alleviated drought damage to membranes; increased soluble sugar and soluble protein content, increased relative water content of leaves; improved photosynthetic performance, promoted the growth and development of seedlings under drought stress, facilitated stem elongation and biomass accumulation, and improved the drought resistance of wheat seedlings. The results of the artificial simulation experiment were more stable, and the experimental process was easier and more controllable.
3.A nutrient solution containing 20% polyethylene glycol-6000 was used to simulate the drought environment to screen the induced drought resistance activities of six derivatives. The results showed that all the six derivatives could induce drought resistance in wheat seedlings, and the drought resistance activity was 3K-B > 9K-G > 1K-B > 9K-B > 3K-G> 1K-G. The configuration of aminobutyric acid and the molecular weight of chitosan in the derivatives could affect the induced drought resistance activity, especially the configuration of aminobutyric acid, and the derivatives containing β -aminobutyric acid had better drought resistance activity. 3K-B has the strongest drought-resistance inducing activity, and the biomass increased by more than 70% compared with the drought group and more than 40% compared with 3K, B and 3KB group.
4.Based on the results of drought activity screening, the best active derivative 3K-B was selected and the metabolic response of wheat seedlings to chitosan-aminobutyric acid derivatives was further investigated using a metabolomic approach based on UHPLC-Q-TOF-MS technique. The metabolomic results showed that 20, 18, 15, 26, 24, and 28 differential metabolites were obtained in the normal culture, salicylic acid, β-aminobutyric acid, chitosan, derivative, and mixture treatment groups, respectively, compared with the drought control group. Combination of different metabolites KEGG metabolic pathway enrichment analysis found that compared to the drought group, the derivative treatment may mitigate the effects of drought by regulating sugar metabolism, amino acid and nucleotide metabolism of wheat seedlings, induced down-regulation of many amino acid metabolism and up-regulation of purine and pyrimidine metabolism, and promoted protein accumulation; induced up-regulation of glucose, fructose and mannose contents, reduced cellular osmotic potential and improved water retention capacity of leaves; induced the up-regulation of plant hormones such as traumatic acid and indole lactic acid to promote the growth of wheat seedlings. The 3K-B treatment mainly regulated the metabolism of traumatic acid, sugar, nucleic acid and fatty acid metabolism, significantly up-regulated nucleotide metabolism, and more significantly regulated amino acid metabolism in wheat compared with other exogenous substances, further revealing that the derivatives could regulate carbon and nitrogen metabolism and improve the drought tolerance of wheat seedlings.
A total of six novel chitosan-aminobutyric acid derivatives with two configurations were prepared in this thesis, and the drought resisitance-inducing activity of the derivatives was correlated with the molecular weight of chitosan and the configuration of aminobutyric acid. The drought-inducing activity of the derivative 3K-B obtained by modifying 3000 Da chitosan with β-aminobutyric acid was the strongest. 3K-B may activate specific signaling pathway to adjust the synthesis of certain proteins to regulate drought resistance in wheat. The present study lays the foundation for the development of novel plant drought-resistant agents. |
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