• Leptolyngbya angustata was isolated from saline-alkali soil. • EPS secreted by the strain can absorb NaCl. • The strain relieves oxidative damage in NaCl-treated alfalfa. • The strain attenuates salt stress via regulating glutathione metabolism. • The strain regulates salt stress response via enhancing photosynthesis. A novel cyanobacterium, Leptolyngbya angustata strain HHW, was isolated from coastal saline-alkali soil, and its potential to alleviate salt stress in alfalfa (Medicago sativa) was investigated. Hydroponic experiments revealed that the application of strain HHW markedly increased the growth of alfalfa seedlings under 100 mM NaCl stress. This growth promotion was associated with enhanced antioxidant enzyme activities, improved glutathione metabolism, and increased chlorophyll content. Strain HHW treatment also led to a marked increase in the secretion of extracellular polymeric substances (EPS) into the culture medium; EPS played a vital role in adsorbing NaCl, thereby reducing salt accumulation in alfalfa seedlings and eliminating the deleterious effects of salt stress on plant growth. Transcriptomic analysis of alfalfa leaves showed that the inoculation of strain HHW upregulated key genes involved in glutathione metabolism, photosynthesis (including photosystems I and II, and antenna proteins), and the Calvin cycle. Our findings indicate that L. angustata HHW enhances alfalfa salt tolerance by modulating multiple physiological and molecular pathways, primarily through reinforcing antioxidant defences and restoring photosynthetic capacity. The present study highlights the potential of this cyanobacterial strain as a promising biofertilizer candidate for plants under salt stress.
Zhang et al. (Fri,) studied this question.