Symbiosis of nodule bacteria with perennial xerophyte leguminous plants of Central Asia

Abstract

From nodules of perennial xerophyte desert leguminous plants – Ammodendron conollyi, Astragalus villossimus, Astragalus unifoliolatus – 151 bacterial isolates have been isolated. The study of nodulation showed that AC8-1, AC11, AC21, AC1-1, AC12-1 isolates (from Ammodendron conollyi), AV1, AV8-1, AV9, AV26-1, AV36-1 isolates (from Astragalus villossimus) and AU17-1, AU30-1, AU30-2, AU20-1, AU23 isolates (from Astragalus unifoliolatus) formed an effective nitrogen-fixing symbiosis with the host plants. As a result of 16S rRNA gene study of the salt-resistant nodule bacteria it has been determined that bacteria were related to Rhizobium, Burkholderia and Achromobacter genera. The study of isolates growth has revealed that there were fast-growing and moderately-grow- ing isolates that possessed with doubling-time varying from 20 to 45 min. Their examination for antibiotic-resistance showed that the number of bacterial colonies of selected strains decreased to some extent in the presence of chloramphenicol, but in all strains the resistance to antibiotics was detected. The further investigations of resistance of the formed symbiosis to stresses (drought, salinity) showed that at 6.41% of moisture the maximal height and biomass of inoculated plants of Ammodendron conollyi were 21 cm and 2320 mg, but at 3.8% moisture the height reduced by 4 times (up to 4.5 cm) and the biomass – by 11 times (203 mg). The analogous effect was observed in Astragalus villossimus and Astragalus unifoliolatus symbiosises. The salinity equal to 100-200 mM NaCl did not affect practically on normal growth and development of desert leguminous plants symbiosis, while for Astragalus villossimus such affecting concentration comprised up to 100 mM NaCl. The light microscopy and electron microscopy of Astragalus villossimus nodule sections showed that V1 nodule bacteria strain efficiently colonized the internal space within nodules, where they were transformed into bacteroids. At 100 mM NaCl salinity concentration the colonization of nodule bacteria within nodule plant cells reduced in comparison with control nodules of plants grown in non-salted conditions.