Effective microorganisms modify protein and polyamine pools in common bean (Phaseolus vulgaris L.) plants grown under saline conditions

• Toxic effects generated by soil salinity were completely overcome by EM application.
• EM application alleviated salt toxicity on plant growth and productivity.
• EM treatment modified polyamine pool under saline conditions.
• Salt-induced reduction in seeds protein content was reversed by EM application.
• EM application significantly reduced the oxidative damage.

No information is available regarding the influence of effective microorganisms (EM) on protein synthesis and polyamine balance in plants grown under saline conditions. Thus, as a first approach, this study sheds light on some different mechanisms that may protect EM-treated plants against salt excess. The response of common bean (Phaseolus vulgaris L.) cv. Nebraska to soil salinization [0.1 dS m−1 (non-saline), 2.5 and 5.0 dS m−1] and/or EM application was investigated. Plants grown in saline soils exhibited a significant decline in productivity, membrane stability index, nitrate reductase activity, nitrate and protein content, K+ concentration, and K+/Na+ ratio. However, EM application ameliorated the deleterious effects of salinity and significantly improved the above parameters. Soil salinity induced oxidative damage through increased lipid peroxidation and hydrogen peroxide content. EM application significantly reduced the oxidative damage. Polyamines responded to salinity stress by increasing its content, particularly putrescine level. The EM treatment changed the polyamine balance under saline conditions, a high increase in spermidine and spermine levels was observed. Moreover, EM application significantly reduced the activities of diamine oxidase and polyamine oxidase in salt-stressed plants. Both the modulation of polyamine pool and the regulation of protein synthesis can be one of the most important mechanisms used by EM-treated plants to improve plant adaptation to saline soils.