Differential salt stress responses and the role of polyamine metabolism in Lotus japonicus ecotypes

Abstract Salt stress represents a critical challenge to global agriculture, reducing productivity and threatening food security. Its impacts are particularly severe in legumes, vital for sustainable agriculture. In this study, we investigated the differential responses to salt stress in two Lotus japonicus ecotypes, MG-20 (tolerant) and Gifu (sensitive), focusing on polyamine metabolism. Plants were exposed to 100 mM NaCl for two weeks, and various physiological and biochemical parameters were measured. MG-20 exhibited smaller reductions in biomass and maintained a higher Na⁺/K⁺ ratio and chlorophyll stability compared to Gifu, indicating greater salt tolerance. Polyamine (putrescine, spermidine, spermine) analysis revealed significant increases in putrescine levels in MG-20 roots and leaves, while Gifu showed inconsistent accumulation patterns. Gene expression analysis indicated enhanced LjADC1 expression in MG-20 roots, correlating with higher putrescine levels and salt tolerance. These findings suggest that MG-20’s superior tolerance may be attributed to its ability to modulate polyamine metabolism more effectively under salt stress conditions. These findings highlight the critical roles of polyamine metabolism and specific biosynthetic pathways in conferring salt stress resilience in Lotus japonicus , providing insights for the development of stress-tolerant crops.