Free-living bacteria that actively colonize plant roots and provide positive effects on plant development are called plant-growth promoting. Plant growth-promoting bacteria can promote plant growth and use their own metabolism to solubilize phosphates, produce hormones and fix nitrogen, and they can directly affect plant metabolism. PGPR also increase plant absorption of water and nutrients, improving root development and increasing plant enzymatic activity; moreover, PGPR can promote other microorganisms as part of a synergistic effect to improve their effects on plants, promoting plant growth or suppressing pathogens. Many studies have shown several benefits of the use of PGPR in maize and sugarcane crops. These bacteria are an excellent alternative to farmers to reduce chemical fertilization and pesticide input without promoting the environment impact and yield-reducing. The present review is an effort to elucidate the concept of rhizobacteria in the current scenario and their underlying mechanisms of plant growth promotion with recent updates. The latest paradigms of a wide range of applications of these beneficial rhizobacteria in both crops maize and sugarcane have been presented explicitly to garner broad perspectives regarding their functioning and applicability. The results from several studies have shown that the utilization of PGPR in maize and sugarcane is the great alternative to farmers face the challenge the modern agriculture.
Aim To investigate the plasma concentrations of glucose, insulin and tumour necrosis factor‐α (TNF‐α) of rats with maternal apical periodontitis (AP) and to explore the effect of maternal inflammation on the initial steps of insulin signalling and the inflammatory pathway in the gastrocnemius muscle (GM) and periepididymal white adipose tissue (pWAT) of adult offspring. Methodology Fifteen female Wistar rats were distributed into a control group (CN), a group with 1 tooth with AP (1AP) and a group with 4 teeth with AP (4AP). Thirty days following induction of AP, female rats from all groups were mated with healthy male rats. When male offspring reached 75 days of age, plasma concentrations of glucose, insulin and TNF‐α were quantified. Insulin resistance was evaluated by the homoeostasis model assessment of insulin resistance (HOMA‐IR) index. Phosphorylation status of pp185 tyrosine, insulin receptor substrate 1 (IRS‐1) serine, IκB kinase α/β (IKKα/β) and c‐Jun N‐terminal kinase (JNK) in the GM and pWAT were measured by Western blot. Analysis of variance was performed, followed by the Tukey's post hoc test. P values <0.05 were considered to be statistically significant. Results Maternal AP promoted insulin resistance, impaired the initial steps of insulin signalling, significantly increased plasma concentrations of insulin (P < 0.001) and TNF‐α (P < 0.05), and enhanced IKKα/β phosphorylation in the GM and pWAT (P < 0.05) of adult offspring. However, maternal AP did not affect fasting glycaemia and JNK phosphorylation in the GM and pWAT of adult offspring. Conclusions Maternal AP was associated with insulin resistance in adult offspring through alterations in insulin signalling and inflammation pathways. The study provides information on the impact of maternal AP on the development of metabolic alterations such as insulin resistance in adult offspring and reinforces the importance of preventing maternal AP in order to maintain the general health of offspring.
Background Maternal periodontal disease leads to low birth weight (LBW), insulin resistance (IR), increased TNF‐α levels, and alterations in insulin signaling in adult offspring. TNF‐α has been associated with the stimulation of IKKβ/NF‐κB, resulting in the decreased expression of GLUT4. Another mechanism that may be involved in decreasing GLUT4 expression is DNA methylation. This study aimed to evaluate in the adult offspring of rats with periodontal disease: IR, inflammatory pathways, DNA methylation, and expression of GLUT4. Methods Female Wistar rats were distributed into control and experimental periodontal disease groups. Seven days after induction of periodontal disease, both groups were mated with healthy male rats. After weaning, male offspring were distributed into control offspring (CN‐o) and periodontal disease offspring (PED‐o) groups. Body weights were measured from 0–75 days of age. At day 75, the following were measured in the offspring: IR (HOMA‐IR index); TNF‐α and NF‐κBp65 content in the gastrocnemius muscle (GM) by western blotting; IKKα/β, JNK, ERK 1/2, NF‐κBp65, and NF‐κBp50 phosphorylation status in the GM by western blotting; DNA methylation by restriction digest and real‐time PCR(qAMP); and expression of GLUT4 mRNA in the GM by real‐time PCR. Results LBW, IR, increases in TNF‐α, IKKα/β, ERK 1/2, NF‐κBp65, and NF‐κBp50 decreased expression of GLUT4 mRNA were observed in the PED‐o rats. No differences were identified in JNK phosphorylation status and DNA methylation in the evaluated regions of the GLUT4‐encoding gene Slc2a4. Conclusion Maternal periodontal disease causes LBW, IR, activation of inflammatory pathways, and decreased GLUT4 expression in the GM of adult offspring.
The effect of Bacillus subtilis isolates before being used as inoculants is very important. They present various impacts on promotion and characteristics of plant at different stages of growth. This experiment was carried out on maize under greenhouse conditions with eleven treatments of endophytic bacteria and three repetitions. The better isolates under greenhouse conditions were used in the field experiment with four best treatments and six replicates. The traits evaluated under both conditions were height, shoot and root dry matter, and the nitrogen and phosphorus content in the plant and soil and the total number of bacteria in the soil. Under greenhouse conditions, the groups that received Bacillus spp. showed higher amount of soluble phosphorus and total numbers of bacteria compared to control. Under field condition, isolate BS-290 increased the nitrogen and phosphorus concentrations in shoot dry matter, phosphorus concentration in dry soil and the total number of bacteria in the soil, compared to the control. Isolate BS-320 increased the phosphorus concentration in plants and maize yield, which strongly suggests its use as a biological inoculant for maize crops. BS-248, BS 290 and BS-320 isolates promoted the highest maize growth, compared to the other isolates. The results showed that Bacillus subtilis isolates that promote plant growth did not increase similar traits in all plants and the behavior has been highly isolate-dependent. This finding shows that the isolates had a preference and certain specificity on each individual trait.
Mineral and organic fertilization can be optimized by using rhizobacteria which increases dry matter, yield, and nutrients in the soil and plant, among the other biological inputs. However, the discovery of single microbes or a consortium that can benefit plants has been a challenge. In this context, this study aimed to evaluate the effects of Bacillus subtilis and Bacillus pumilus combined with mineral fertilization and sugar and alcohol industry by-products in presprouted and the initial growth phase of sugar cane seedlings. The study was carried out in two phases. Phase 1 included presprouted seedlings with T1 = untreated control, T2 = B. subtilis, T3 = B. pumilus, and T4 = B. subtilis + B. pumilus treatments. Phase 2 included the same treatments with four types of fertilization: F1 = mineral fertilization, F2 = mineral fertilization + vinasse, F3 = mineral fertilization + filter cake, and F4 = mineral fertilization + filter cake compost. Of the phase 1 treatments, T2 (B. subtilis) was the best promoter of root growth and the total dry matter compared to the control with an increase of 23.0% compared to the control. In phase 2, B. pumilus application, increased the total dry matter by 13%, the number of tillers by 37%, and the diameter of the tillers by 48% when combined with mineral fertilization. The combined application of B. subtilis and B. pumilus increased the phosphorus content by 13% in soil treated with mineral fertilization and filter cake compost. The results of the this study strongly suggest that the use of B. subtilis and B. pumilus together with these by-products can improve soil fertility parameters and decrease adverse effects associated with vinasse fertilization, in addition to providing shoot and root growth and providing collective synergy for a high yield of sugarcane production with environmental benefits.
Plant growth-promoting bacteria (PGPB) and humic substances (HSs) are promising options for reducing the use of pesticides and mineral fertilizers. Although many studies have shown the effects of PGPB and HSs separately, little information is available on plant responses to the combined application of these biostimulants despite the great potential for the simultaneous action of these biological inputs. Thus, the objective of this review is to present an overview of scientific studies that addressed the application of PGPB and HSs to different crops. First, we discuss the effect of these biostimulants on biological nitrogen fixation, the various effects of the inoculation of beneficial bacteria combined with the application of HSs on promoting the growth of nonleguminous plants and how this combination can increase bacterial colonization of plant hosts. We also address the effect of PGPB and HSs on plant responses to abiotic stresses, in addition to discussing the role of HSs in protecting plants against pathogens. There is a lack of studies that address the role of PGPB + HSs in biocontrol. Understanding the factors involved in the promotion of plant growth through the application of PGPB and HSs can assist in the development of efficient biostimulants for agricultural management. This approach has the potential to accelerate the transition from conventional cultivation to sustainable agrosystems.
Plant growth-promoting endophytic microorganisms in agriculture have been expanding in Brazil and are an excellent strategy to face the challenges of current agriculture, such as reducing production costs with fewer environmental impacts, without detriment to productivity. However, little is known about the factors that can affect the colonization of endophytic such as inoculant concentration and mineral fertilization. The present study aimed to evaluate the influence of these factors on soybean and maize crops and found that for soybean crops, the highest Bacillus subtilis concentration of 1 × 104 and 1 × 1010 CFU ml−1 promoted the highest number of recovered bacteria, when there was no mineral fertilization. However, mineral fertilization limited the number of recovered bacteria, suggesting that mineral fertilization interferes with endophytic colonization. For maize crops, the highest number of recovered bacteria occurred from the concentration of 1 × 106 CFU ml−1, not differing from the highest concentrations. A mineral fertilization dose of 25% promoted the greatest B. subtilis recovery compared to the other treatments. Regarding plant development, the highest microbial inoculum concentrations did not necessarily promote greater positive growth promotion effects compared to the concentration of 1 × 104 CFU ml−1 for both crops. The results also suggest that the higher number of endophytic bacteria recovered in the plant does not necessarily affect plant growth in the same proportion. For soybean plants, there is a strong tendency that with the increase in the B. subtilis inoculant concentration, the need for mineral fertilization doses to achieve the same plant development is consequently increased, and inoculations with 1 × 105 and 1 × 106 CFU ml−1 with fertilization doses between 44% and 62% are the ideal combinations for greater plant development. In maize plants, the best growth promotion response (height) was obtained using inoculation concentration of 1 × 102 and 1 × 1010 CFU ml−1, increasing according to the increase in fertilization doses. The findings suggest, for soybean crop, that these high inoculum concentrations required more photosynthetic metabolites from the plants and more nutrients from the soil. Thus, the need for mineral fertilization for plant growth must be increased.
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