Abstract
Beneficial plant–microbe interactions lead to physiological and biochemical changes that may result in plant-growth promotion. This study evaluated the effect of the interaction between sugarcane and endophytic bacterial strains on plant physiological and biochemical responses under two levels of nitrogen (N) fertilization. Six strains of endophytic bacteria, previously selected as plant growth-promoting bacteria (PGPB), were used to inoculate sugarcane mini stalks, with and without N fertilization. After 45 days, biomass production; shoot nutrient concentrations; foliar polyamine and free amino acid profiles; activities of nitrate reductase and glutamine synthase; and the relative transcript levels of the GS1, GS2, and SHR5 genes in sugarcane leaves were determined. All six endophytic strains promoted sugarcane growth, increasing shoot and root biomass, plant nutritional status, and the use efficiency of most nutrients. The inoculation-induced changes at the biochemical level altered the foliar free amino acid and polyamine profiles, mainly regarding the relative concentrations of citrulline, putrescine, glycine, alanine, glutamate, glutamine, proline, and aspartate. The transcription of GS1, GS2, and SHR5 was higher in the N fertilized seedlings, and almost not altered by endophytic bacterial strains. The endophytic strains promoted sugarcane seedlings growth mainly by improving nutrient efficiency. This improvement could not be explained by their ability to induce the production of amino acid and polyamine composts, or GS1, GS2, and SHR5, showing that complex interactions may be associated with enhancement of the sugarcane seedlings’ performance by endophytic bacteria. The strains demonstrated biotechnological potential for sugarcane seedling production.
Highlights
Throughout their evolution, plants have developed a complex set of mechanisms for environmental adaptation
One such mechanism is the association with beneficial microorganisms, such as endophytic and rhizosphere bacteria known as plant-growth-promoting bacteria (PGPB)
At T0, the seedlings inoculated with endophytes strains produced significantly higher shoot biomass than plants without inoculation and there were no significant differences in root biomass production among treatments (Table 2)
Summary
Throughout their evolution, plants have developed a complex set of mechanisms for environmental adaptation. One such mechanism is the association with beneficial microorganisms, such as endophytic and rhizosphere bacteria known as plant-growth-promoting bacteria (PGPB). The plant–bacteria interaction, through a complex array of mechanisms, can result in plant growth-promotion due to increased nutrient uptake, nitrogen fixation, or phytohormone production, or indirectly due to the phytopathogen suppression [2]. The nutritional benefits and growth stimulation can be directly linked to the improvement in plant nitrogen (N) status by biological nitrogen fixation (BNF) activity, triggered by diazotrophic bacteria which possess the nif gene, or to the production of auxinrelated compounds, and to other mechanisms such as phosphate solubilization and siderophore production—all desirable characteristics of PGPB [3,4].
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