LAUSR

Background and aimsThe endophytic fungus Epichloë bromicola forms mutualistic symbiotic associations with wild barley (Hordeum brevisubulatum) in the saline-alkali areas of northwestern China. E. bromicola enhances the tolerance of H. brevisubulatum to salt stress. Because plant polyamine metabolism is closely related to microbial infection and tolerance to diverse abiotic stresses, we hypothesized that in symbiotic plants polyamine modification may result from E. bromicola infection, and that improved tolerance to abiotic stress by the presence of this endophyte might be related to polyamine modification. Our focus in this study was to investigate whether E. bromicola affects polyamine metabolism in host plants under salt stress.MethodsE. bromicola infected (E+) and endophyte free (E-) wild barley plants were subjected to NaCl treatments (0, 100, 200 and 300 mM). Dry weight, diamine putrescine (Put), triamine spermidine (Spd) and tetramine spermine (Spm) content and the content of their free, soluble conjugated and insoluble bound forms were measured after 21 d exposure to stress.ResultsE. bromicola infection led to significant amelioration of salt stress in H. brevisubulatum. The presence of the endophyte significantly increased dry weight, spermidine and spermine content, but decreased putrescine content and the putrescine: (spermidine + spermine) ratio. E. bromicola infection also lowered the proportion of putrescine in total polyamines, but increased the proportion of spermidine and spermine in total polyamines. Furthermore, E. bromicola infection significantly increased the proportion of insoluble bound forms of polyamines, and decreased the proportion of free forms of polyamines and soluble conjugated forms of polyamines.ConclusionsH. brevisubulatum salinity stress tolerance induced by E. bromicola infection correlated with enhanced conversion of putrescine to spermidine and spermine, as well as improved shift ability from free forms and soluble conjugated forms of polyamines to insoluble bound forms of polyamines.