| A series of adjustments in agricultural production relations and the growth of integrated productivity have led to an increasing share of chemical inputs such as fertilisers and hormones,taking into account the needs of society for food and the goal of achieving agricultural export development.Although the advent of chemical fertilisers has greatly reduced soil cultivation,their irrational use on a large scale has not only caused soil acidification,nutrient loss and ecological imbalances,but also modern diseases such as cancer and bronchitis.In order to protect humans and the ecosystem from toxicity,microbial-based production and management methods are gradually becoming a good alternative to chemical fertilisers.However,the research of many microbial agents still stops at the level of promotion,and there are few studies on the overall improvement of vegetable nutritional quality and antioxidant propertie.Therefore,in this study,Bacillus cereus LSE01(LSE01),a plant endophytic bacterium with probiotic function isolated from the stem of the hyperaccumulator Solanum nigrum L,was used as a biological inoculant for the overall improvement of nutritional quality as a major nutrient source for vegetables was thoroughly investigated,and the growth-promoting effects were also compared to those of host plant endophytes,thus providing guidance for future growth-promoting studies.In addition,the differential proteins of inoculated soybean sprouts were analyzed by LC-MS/MS technique to reveal the uptake mechanism of LSE01 bacterial agent,which opens new perspectives for the development of resilient production systems required to promote vegetable yield and quality and to explore the molecular mechanisms of plant endophyte-host plant interactions.The main research results are as follows:(1)The growth-promoting effect of LSE01 on vegetables was verified by pot experiments,and it was found that inoculation with LSE01 significantly increased the growth index of soybean sprouts and red leaf lettuce.Overall,in all six groups of control experiments,the trend after both vegetable treatments showed LSE01 >Escherichia coli(E-coli)> LSE01 metabolites(LSE01 M)> Escherichia coli metabolites(E-coli M)> Water treatment(C)> LB.The endophytic bacterium LSE01 was found to be able to colonize the entire life cycle of the two vegetables as the dominant colony and always maintain a high number of strains through the regular partitioning experiments.For economic benefits,the average yield of LSE01-treated red leaf lettuce and soybean sprouts increased by 232.32% and 25.65%,respectively.Similarly,the average economic income of the two vegetables increased from 6726(?)/ha and 9383 (?)/ha to 8439 (?)/ha and 31182 (?)/ha,respectively.In addition,after reinoculation of six endophytic strains obtained from the rhizomes of soybean sprouts to the seeds of the host plants,it was found that most of the endophytic bacteria still had limited and inhibitory effects on the growth of soybean sprouts,and the two endophytic bacteria B1 and B2 W had positive effects on all growth indexes,but their growth-promoting effect was much lower than LSE01.(2)Experimental results regarding protein content,photosynthetic pigment content,phenolic compounds and antioxidant enzyme activity found that the addition of LSE01 presented different degrees of influence on nutritional quality.The most significant effect was for protein content,which increased by 133.09% and 110.34%in the inoculated soybean sprouts and red leaf oil wheat,respectively,compared to the C treatment.Moreover,photosynthetic pigments such as chlorophyll a,chlorophyll b,carotenoids,phenolic compounds,vitamin C and antioxidant enzyme activities were also significantly higher than those of other controls(p<0.05),in which the total chlorophyll content of red leaf lettuce treated with LSE01 increased by 34.38%,and the vitamin C content was increased by 149.93% and 55.56%,respectively.For total phenol and total flavonoid content,the overall trend for both vegetables was basically LSE01 > E-coli ≥ LSE01 M > E-coli M > C > LB.Meanwhile,both vegetables exhibited higher antioxidant enzyme activities after LSE01 treatment,especially the PPO of red leaf lettuce and the SOD activity of soybean sprouts had a greater effect,increasing by 49.38% and 64.55%,respectively.(3)Proteomic analysis of the hypocotyl of soybean shoots inoculated with LSE01 identified a total of 1312 differential protein expression sites,of which 52 proteins were down-regulated and 101 were up-regulated.Secondly,the GO annotation results showed that most of the differential proteins involved were biological processes,including translation,structural constituent of ribosome,r RNA binding and ribosome,which are closely related to the synthesis of vegetable proteins.In addition,there is a large proportion of photosynthesis-related proteins,which directly influence vegetable development,nutrient availability and photosynthetic pigment content.On the other hand,a total of 54 different metabolic pathways were retrieved through the KEGG database and the enrichment of these metabolic pathways had a positive impact on promoting cell elongation,increasing antioxidant levels and promoting the synthesis of nutrients such as proteins.(4)Four types of sprouts were selected using 1/4 Hoagland’s nutrient solution and deionised water as the base medium for an investigation about pervasiveness.The growth indicators and morphological analysis of stem length,stem diameter,plant length,leaf length and leaf width revealed that both groups inoculated with LSE01 showed a more pronounced growth promoting effect,with LSE01+H(LSE01+Hoglan nutrient solution)showing the most prominent and stable yield,but for both yellow and mung bean sprouts the number of deaths accompanying this condition also increased.In addition,the experiment further explored the effect of microbial agents on the quality of different sprouts as represented by the protein content index.The results showed that all four sprouts inoculated with LSE01 showed a more significant increase in protein content,except for wheatgrass,with the protein content of black bean sprouts treated with LSE01+C(LSE01+water treatment)being approximately5.48 times higher than that of the C+C(Control)treatment.However,plants cultured under LSE01+H conditions are susceptible to external factors such as variety and plant resistance.In contrast,the positive effects of LSE01+C culture conditions on the protein content of vegetables are more stable and have wider generalizability. |
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