Genotypic Variation of Endophytic Nitrogen-Fixing Activity and Bacterial Flora in Rice Stem Based on Sugar Content

Abstract

Enhancement of the nitrogen-fixing ability of endophytic bacteria in rice is expected to result in improved nitrogen use under low-nitrogen conditions. Endophytic nitrogen-fixing bacteria require a large amount of energy to fix atmospheric nitrogen. However, it is unknown which carbon source and bacteria would affect nitrogen-fixing activity in rice. Therefore, this study examined genotypic variations in the nitrogen-fixing ability of rice plant stem as affected by non-structural carbohydrates and endophytic bacterial flora in field-grown rice. In the field experiments, six varieties and 10 genotypes of rice were grown in 2017 and 2018 to compare the acetylene reduction activity (nitrogen-fixing activity) and non-structural carbohydrates (glucose, sucrose, and starch) concentration in their stems at the heading stage. For the bacterial flora analysis, two genes were amplified using a primer set of 16S rRNA and nitrogenase (NifH) gene-specific primers. Next, acetylene reduction activity was correlated with sugar concentration among genotypes in both years, suggesting that the levels of soluble sugars influenced stem nitrogen-fixing activity. Bacterial flora analysis also suggested the presence of common and genotype-specific bacterial flora in both 16S rRNA and nifH genes. Similarly, bacteria classified as rhizobia, such as Bradyrhizobium sp. (Alphaproteobacteria) and Paraburkholderia sp. (Betaproteobacteria), were highly abundant in all rice genotypes, suggesting that these bacteria make major contributions to the nitrogen fixation process in rice stems. Gammaproteobacteria were more abundant in CG14 as well, which showed the highest acetylene reduction activity and sugar concentration among genotypes and is also proposed to contribute to the higher amount of nitrogen-fixing activity.

Endophytic nitrogen-fixing bacteria DX120E inoculation altered the carbon and nitrogen metabolism in sugarcane

“…The role of endophytic N-fixing bacteria in improving carbon and sugar metabolisms, photosynthetic carbon assimilation, starch and sucrose metabolism, carbohydrate transport and utilization process in plants has been proven ( Coruzzi and Zhou, 2001 ; Zheng, 2009 ). The sucrose formed by photosynthesis in sugarcane leaves is transported to the phloem, loaded to the sieve tube for long-distance transport, and finally unloaded through the phloem into the parenchyma cells in the stem for storage ( Khan et al, 2021 ; Okamoto et al, 2021 ). During the transportation process, part of the sucrose is hydrolyzed to fructose and glucose in the growing part for plant growth.…”

Overview of biofertilizers in crop production and stress management for sustainable agriculture

“…Endophytes isolated from rice such as Bradyrhizobium sp ., Paraburkholderia sp., showed acetylene reduction properties and high sugar content contributing to high nitrogen-fixing ability. High content of sugar in different crops such as sweet potato, pineapple, and sugar has known to assist endophytic N-fixing activity among non-leguminous plants (Okamoto et al, 2021 ).…”

Endophytes and their potential in biotic stress management and crop production

“…But mainly, endophytic bacterial and fungal strains confer propound impacts on the overall health and maintenance of crop plants under different environmental conditions via nitrogen fixation, phosphate solubilization, siderophore, and phytohormones production and by conferring tolerance to various stresses. Additionally, N-fixing endophytes Novosphingobium sediminicola , Ochrobactrum intermedium (from sugarcane) and Bradyrhizobium , Kosakonia , and Paraburkholderia (from rice) carry nitrogen fixation genes ( Muangthong et al, 2015 ; Okamoto et al, 2021 ).…”

“…and Paraburkholderia sp., showed acetylene reduction properties and high sugar content contributing to high nitrogen-fixing ability. High content of sugar in different crops such as sweet potato, pineapple, and sugar has known to assist endophytic N-fixing activity among non-leguminous plants ( Okamoto et al, 2021 ). Acetobacter diazotrophicus and Azoarcus isolated from sugarcane and kallar grass potentially fixed atmospheric nitrogen up to 150 kg N ha –1 year –1 ( Gupta et al, 2012 ).…”