Biochemical Responses of Wheat Plants Primed with Ochrobactrum pseudogrignonense and Subjected to Salinity Stress

A large number of bacteria were isolated from the rhizosphere of Imperata cylindrica, a facultative halophyte, and the most tolerant one with an ability to grow under 10% sodium chloride in vitro was selected and designated as IP8. This was identified to be Ochrobactrum pseudogrignonense on the basis of 16SrDNA analysis and showed positive plant-growth-promoting traits in vitro. Growth of wheat was enhanced by the bacterium under both non-stressed and salt-stressed conditions. Alleviation of salt stress by the bacterium was evident by the biochemical responses such as reduction in hydrogen peroxide accumulation as well as enhanced proline accumulation and antioxidative mechanisms. Activities of peroxidase, catalase, ascorbate peroxidase, and glutathione reductase were enhanced after salinity treatment, but that of superoxide dismutase was not. Treatment with IP8 and sodium chloride showed enhanced activities, and when compared to sodium chloride alone, peroxidase showed further up-regulation in some cultivars and superoxide dismutase also showed significantly increased activities. Salinity had no effect on activities of defense enzymes in general. Activities of defense enzymes were significantly enhanced by IP8 alone or in addition to salinity treatment. Microarray analysis revealed that 282 genes were down-regulated and 6022 up-regulated after application of O. pseudogrignonense under salt stress induction by 200 mM sodium chloride. Among the up-regulated genes were those of peroxidase, phenylalanine ammonia lyase, chitinase, glucanase, as well as germin-like proteins, histone H2B, and sulfur-rich thionin-like proteins. Genes for ascorbate peroxidase, lipid transfer proteins, and salt stress responsiveness were among the down-regulated ones.