Fungal endophyte Epichloe bromicola infection regulates anatomical changes to account for salt stress tolerance in wild barley (Hordeum brevisubulatum)

Background and aims Plants can minimize the adverse effects of salinity by modifying morphological and anatomical features. Previous studies showed that endophytic Epichloe bromicola play an important role in improving wild barley (Hordeum brevisubulatum) salinity tolerance. The aim of this work is to understand whether Epichloe endophyte affects the anatomical structures of host H. brevisubulatum under salinity environments. Methods Seedlings of E. bromicola infected (E+) and E. bromicola free (E-) H. brevisubulatum were treated with different NaCl concentrations, with the control seedlings being grown without NaCl. Anatomical structures of roots, stems and leaves were observed by making paraffin sections with double staining dehydration methods (safranin and fast green). Results NaCl treatments significantly affected the anatomical structure of H. brevisubulatum. Vascular tissue area throughout the leaf, stem and root decreased as the NaCl concentration increased. Thickness of epidermis in stems and leaves, and the cortex in roots also decreased with salt level increases. Endodermis thickness, epidermis thickness and stele area in roots were increased under salinity stress. The presence of Epichloe endophyte regulated some anatomical structure modifications. Epichloe infection was associated with significant higher conducting tissues (including leaf xylem, leaf phloem, stem vascular bundles, stem xylem vessels and root meta-xylem area). The increased thickness of leaf veins, epidermis in stems, cortex and endodermis in roots were also associated with Epichloe endophyte infection under NaCl stress. Conclusions The presence of Epichloe endophyte ameliorated adverse effects of salinity on H. brevisubulatum. We observed specific changes of anatomical structures that may help in inhibiting water loss and inhibiting decrease of transport capacity for better conduction of water, nutrients, photosynthates and re-translocation of assimilates to suppress negative effects of salinity and enhance the tolerance of H. brevisubulatum to salt stress.