Arsenic (As) contamination in soil represents a major challenge to global agriculture, threatening crop productivity and food security, making the development of effective mitigation strategies essential for sustainable farming. Synthetic bacterial communities (SynCom) improve host plants ability to withstand As stress by several mechanisms. It is well known that polyamines (PAs) strengthen the antioxidant defence system, prevent ethylene formation, preserve cell pH, and shield plant cells from the damaging effects of As, and so forth; nevertheless, it is still unknown how SynCom modify PA metabolism to improve plant resistance to As. Pot experiment was carried out to evaluate how SynCom affects root PA homeostasis, hydrogen peroxide (metabolite associated with PA), genes encoding antioxidant system and expression and activities of PA- associated degrading and synthesizing enzymes in rice subjected to As. SynCom inoculated plants exhibited maximum growth attributes, gene expression of two plasma membrane intrinsic protein, leaf water potential, and chlorophyll contents than non-inoculated plants exposed to As stress. With increased activity of PA catabolic enzymes (copper-containing diamine oxidase, CuAO; polyamine oxidase, PAO) and putrescine synthases (ornithine decarboxylase; arginine decarboxylase, ADC), SynCom inoculated plants resulted in higher putrescine and cadaverine concentrations but lower spermidine and spermine contents. Under As stress, the SynCom inoculated plants resulted in up-regulation of spermine synthase gene, OsSPMS, and down-regulation of PA catabolic enzyme genes (OsCuAO6, OsCuAO8, OsCuAO1 and OsCuAO2) and PA synthase genes (OsADC2 and OsADC1). As stressed plants inoculated with SynCom had higher level of expression in OsPAO1, OsPAO2, OsPAO3 as compared to non-inoculated plants, stimulating reactive oxygen species-associated stress responsiveness signaling through low H2O2 levels by enhancing the genes encoding antioxidant defence system (OsCu/Zn-SOD, OsCAT1 and OsMn-SOD). The results of this study showed that SynCom can alter PA metabolism to improve plants' resistance to heavy metals like As. The inoculation of SynCom emerges as a promising strategy to enhance plant resilience against As toxicity by promoting positive interactions and regulatory stress-responsive pathways. Furthermore, the inoculation of SynCom is a viable approach capable of ameliorating heavy metal stress and improving the productivity of crops in the contaminated soil by fostering positive interactions and stress responsive regulatory mechanisms. (c) 2025 SAAB. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

The detrimental impact of soil salinization on crop productivity and agricultural economy has garnered significant attention. A rhizosphere bacterium with favorable salt tolerance and plant growth-promoting (PGP) functions was isolated in this work. The bacterium was identified as Enterobacter through 16 S rDNA sequencing analysis and designated as Enterobacter sp. JIV1. Interestingly, the presence of putrescine (Put), which had been shown to contribute in reducing abiotic stress damage to plants, significantly promoted strain JIV1 to generate 1aminocyclopropane-1-carboxylic (ACC) deaminase, dissolve phosphorus and secrete indole-3-acetic acid (IAA). However, the synergy of plant growth promoting rhizobacteria (PGPR) and Put in improving plant salt resistance has not been extensively studied. In this study, strain JIV1 and exogenous Put effectively mitigated the inhibitory impact of salt stress simulated by 200 mM NaCl on rice (Oryza sativa L.) growth. The chlorophyll accumulation, photosynthetic efficiency and antioxidant capacity of rice were also significantly strengthened. Notably, the combined application of strain JIV1 and Put outperformed individual treatments. Moreover, the co-addition of strain JIV1 and Put increased soil protease and urease activities by 451.97% and 51.70% compared to that of salt treatment group. In general, Put-assisted PGPR JIV1 provides a new perspective on alleviating the salt-induced negative impacts on plants.