Changes in metabolic profiling of sugarcane leaves induced by endophytic diazotrophic bacteria and humic acids

Abstract

Plant growth-promoting bacteria (PGPB) and humic acids (HA) have been used as biostimulants in field conditions. The complete genomic and proteomic transcription of Herbaspirillum seropedicae and Gluconacetobacter diazotrophicus is available but interpreting and utilizing this information in the field to increase crop performance is challenging. The identification and characterization of metabolites that are induced by genomic changes may be used to improve plant responses to inoculation. The objective of this study was to describe changes in sugarcane metabolic profile that occur when HA and PGPB are used as biostimulants. Inoculum was applied to soil containing 45-day old sugarcane stalks. One week after inoculation, the methanolic extracts from leaves were obtained and analyzed by gas chromatography coupled to time-of-flight mass spectrometry; a total of 1,880 compounds were observed and 280 were identified in all samples. The application of HA significantly decreased the concentration of 15 metabolites, which generally included amino acids. HA increased the levels of 40 compounds, and these included metabolites linked to the stress response (shikimic, caffeic, hydroxycinnamic acids, putrescine, behenic acid, quinoline xylulose, galactose, lactose proline, oxyproline and valeric acid) and cellular growth (adenine and adenosine derivatives, ribose, ribonic acid and citric acid). Similarly, PGPB enhanced the level of metabolites identified in HA-treated soils; e.g., 48 metabolites were elevated and included amino acids, nucleic acids, organic acids, and lipids. Co-inoculation (HA+PGPB) boosted the level of 110 metabolites with respect to non-inoculated controls; these included amino acids, lipids and nitrogenous compounds. Changes in the metabolic profile induced by HA+PGPB influenced both glucose and pentose pathways and resulted in the accumulation of heptuloses and riboses, which are substrates in the nucleoside biosynthesis and shikimic acid pathways. The mevalonate pathway was also activated, thus increasing phytosterol synthesis. The improvement in cellular metabolism observed with PGPB+HA was compatible with high levels of vitamins. Glucuronate and amino sugars were stimulated in addition to the products and intermediary compounds of tricarboxylic acid metabolism. Lipids and amino acids were the main compounds induced by co-inoculation in addition to antioxidants, stress-related metabolites, and compounds involved in cellular redox. The primary compounds observed in each treatment were identified, and the effect of co-inoculation (HA+PGPB) on metabolite levels was discussed.

Humic Acid Enhances the Growth of Tomato Promoted by Endophytic Bacterial Strains Through the Activation of Hormone-, Growth-, and Transcription-Related Processes

“…increasing electrolyte leakage, cell permeability and nutrient accumulation (David et al, 1994) and activating primary and secondary metabolism (Aguiar et al, 2018;Canellas et al, 2019). HA incubation upregulated genes responsible for cellular regulations in mock-inoculated plants, such as transcription factors, receptors and kinases, and altered the transcriptional response of tomato plants to endophytic bacterial strains.…”

“…The protein metabolic pathways were activated by 32A in tomato roots in the HA condition, indicating the activation of nitrogen assimilation with upregulation of genes related to the metabolism of lysine, serine, glycine, cysteine, tyrosine, threonine, glutamine, alanine, arginine, and methionine. Likewise, the nitrogen and secondary metabolism was activated in H. seropedicae HRC54-inoculated tomato plants in the presence of HA (Olivares et al, 2015) and the increased concentration of amino acids and secondary metabolites was found in sugarcane plants inoculated with H. seropedicae HRC54 and G. diazotrophicus PAL 5 in the presence of HA (Aguiar et al, 2018;Canellas et al, 2019). In particular, 32A was able to fix atmospheric nitrogen in vitro (Campisano et al, 2014) and it caused the upregulation of a glutamine synthetase gene in tomato roots in the HA condition.…”

“…Likewise, tomato fruit biomass was increased by H. seropedicae HRC54 and HA through the stimulation of nitrogen and secondary metabolism (Olivares et al, 2015). A mixed inoculum of H. seropedicae HRC54 and Gluconacetobacter diazotrophicus PAL 5 in combination with HA changed the metabolite fingerprints of amino acids, sugars and organic acids in maize and sugarcane seedlings, indicating that the activation of primary and secondary metabolism was partially responsible for the biostimulation effects (Aguiar et al, 2018;Canellas et al, 2019). Although considerable evidence of efficacy exist in literature, the molecular mechanisms of the combined applications of living PGPB and organic biostimulant on crops are less investigated (Bulgari et al, 2015).…”

Adaptation mechanism of mango fruit (Mangifera indicaL. cv. Chaunsa White) to heat suggest modulation in several metabolic pathways

“…In sugar cane, the application of biostimulants such as humic acid to soil increased the concentration of metabolites involved in cellular growth. Ribonic acid was one such metabolite promoting cellular growth in sugar cane, 55 it can be suggested that in mango, ribonic acid may be involved in cellular growth and differentiation. D-Mannose was the monosaccharide identied at the earliest stage during the development of Chaunsa mango fruit, which is known to be a common metabolite between the two metabolic pathways, ascorbate biosynthesis pathway and the primary cell wall synthesis pathway, during tomato fruit development.…”

Humic acids and Herbaspirillum seropedicae change the extracellular H+ flux and gene expression in maize roots seedlings

“…The suitability of HA as an adjuvant to bacterial foliar sprays was demonstrated for field-grown maize, where yields were 65% higher than untreated controls and 40% higher than maize fields treated with HA or bacteria [27]. Moreover, a boost in the metabolic profile of sugarcane leaves induced by HA and PGPB [33] with activation of the glycolysis pathway and enhanced TCA activity resulted in the accumulation of α-ketoglutaric acid, which is a central metabolite in glutamine and glutamic acid synthesis. The stimulation of TCA enzymes by HS was previously reported by Nardi et al [34].…”