The Endophyte Pantoea alhagi NX-11 Alleviates Salt Stress Damage to Rice Seedlings by Secreting Exopolysaccharides

Abstract

Endophytes have the potential to enhance the ability of plants to resist salt stress, improving crop development and yield. Therefore, in this study, we isolated an endophyte that produced large amounts of exopolysaccharides (EPSs) from the roots of sea rice and examined its effects on the physiological responses of rice (Oryza sativa L. ssp. japonica "Nipponbare") seedlings to salt stress using hydroponic experiments. The endophyte was named Pantoea alhagi NX-11 based on its morphological characteristics and 16S ribosomal DNA (rDNA) sequence alignment. Rice seedlings that had been inoculated with P. alhagi NX-11 exhibited a 30.3% increase in fresh weight, a 28.6% increase in root length, a 51.6% increase in shoot length, and a 26.3% increase in chlorophyll content compared with control seedlings under normal conditions. In addition, inoculated rice seedlings had a 37.5% lower malondialdehyde content, a 133% higher K + /Na + ratio, and a 52.8% higher proline content after 7 days under salt stress, as well as up-regulated expression of proline synthase, down-regulated expression of proline dehydrogenase, and enhanced antioxidant enzyme activities. Interestingly, rice seedlings that were inoculated with an EPS-deficient strain named NX-11 eps− that was obtained by atmospheric and room temperature plasma (ARTP) mutagenesis were damaged by salt stress and had similar physiological and biochemical indicators to the control group. Therefore, we speculate that the ability of P. alhagi NX-11 to enhance the salt tolerance of rice seedlings is related to the EPSs it produces.

Roles of Plant Growth-Promoting Rhizobacteria (PGPR) in Stimulating Salinity Stress Defense in Plants: A Review

“…The increased activities of AEs and/or the elevated accumulations of osmoregulators in PGPB-inoculated plants were reported by Li and Jiang [ 42 ], Akram et al [ 45 ], Vaishnav et al [ 47 ], Khalid et al [ 58 ], Kim et al [ 96 ], Habib et al [ 97 ], Kang et al [ 104 ], Zhu et al [ 107 ], Halo et al [ 151 ], Bharti et al [ 152 ], El-Esawi et al [ 153 ], Vimal et al [ 154 ], El-Nahrawy and Yassin [ 155 ], Sun et al [ 156 ]. For instance, the activity of ROS-scavenging enzymes SOD, CAT of Enterobacter -treated okra plants was the highest amongst all treatments, in parallel with their highest vegetative parameters SFW, SDW, RFW, and RDW [ 97 ].…”

Multi-Trait Wheat Rhizobacteria from Calcareous Soil with Biocontrol Activity Promote Plant Growth and Mitigate Salinity Stress

“…All assays were performed as described in Materials and Methods [ 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 ]. Table 3 was constructed according to the estimates of response level of each bacterial strain to the applied beneficial traits (strong, medium, low, not applicable).…”

“…Therefore, maintaining the ecological balance of the agricultural ecosystems requires the imposition of drastic solutions to the problem [ 3 , 40 ]. Many studies prove the effect of PGPR on the alleviation of salt stress on crop plants [ 13 , 41 , 42 , 43 , 44 , 45 ]. Arthrobacter protophormiae (SA3) and Dietzia natronolimnaea (STR1) enhanced photosynthetic efficiency [ 42 ], IAA content and other beneficial traits in wheat, Klebsiella , Pseudomonas , Agrobacterium , and Ochrobactrum in peanut [ 43 ], Pseudomonas putida UW4 and P. migulae 8R6 effected on Camelina sativa (camelina) [ 44 ], Micrococcus yunnanensis , Planococcus rifietoensis , and Variovorax paradoxus on Beta vulgaris [ 45 ], Bacillus licheniformis AP6 and Pseudomonas plecoglossicida PB5 with proven biofilm formation can facilitate sunflower growth by improving physiological and biochemical attributes [ 46 ], Bacillus megaterium in Zea mays , Azospirillum sp.…”

Secondary Metabolites From Halotolerant Plant Growth Promoting Rhizobacteria for Ameliorating Salinity Stress in Plants

“…Similarly, Mahmood et al (2016) concluded that under salinity stress, treatment of mung bean with EPS producing Enterobacter cloacae and Bacillus drentensis enhanced nutrient availability and water uptake in plants by the formation of biofilm in the root zone. In another study, inoculation of EPS producing endophyte, Pantoea alhagi NX-11 improved salt tolerance of rice seedlings by improving the antioxidant activity resulting in better growth in comparison to the plants treated with EPS mutant NX-11 eps− (Sun et al, 2020). Likewise, treatment of maize with EPS producing Azotobacter chrococcum strains C5 and C9 under saline conditions alleviated the saline stress by several means i.e., increasing K + /Na + ratio and ions uptake (Na + , K + , Ca 2+ , Mg 2+ ), chlorophyll content, and accumulation of proline and polyphenols (Rojas-Tapias et al, 2012).…”