Effect of salt stress on apoplastic barriers in roots and leaves of two barley species

Abstract

In this study, the responses of 12 d old cultivated barley (<em>Hordeum vulgare</em> L. <em>spp.vulgare</em>) cv Scarlett and a wild accession (Hordeum vulgare spp. sponataneum) from Pakistan (ICB181243) to salt stress of concentrations 80 mM, 180 mM and 275 mM corresponding to water potential equivalents of -0.4 MPa, -0.8 MPa and -1.2 MPa were investigated and compared. The shoot and root responses at morphological, histochemical, biochemical, molecular and physiological levels in terms of stress adaptability and tolerance were studied. The salt stress significantly reduced the growth in both species and was prominent in Pakistan wild barley. Strong apoplastic suberin was formed in both the barley species and also a differential pattern in the degree of suberization was observed between the two genotypes. Further transcriptomic studies in 180 mM stressed roots revealed positive regulation of suberin related genes; and differential regulation of aquaporins and salt stress related genes in both species. Mineral nutrient analysis showed significantly elevated Na accumulation and decreased Ca and K ion levels in both shoots and roots in both genotypes. As a consequence of increased Na levels osmotic adjustment through proline occurred in both barley genotypes. Significant increase in proline levels, especially at higher salt stress concentrations of 180 mM and 275 mM was observed in the leaves and roots of both Scarlett and Pakistan wildtype. The osmotic potential within the roots reduced significantly than the control. The fold decrease in the stressed roots did not vary much between the genotypes. The results from physiological studies also conform to the salinity induced effect through reduced stomatal conductance and photosynthetic yield in the leaves. The wax and cutin amounts varied specifically in leaf 2 due to its detrimental development in salinity. Thus, these results, especially between the cultivar Scarlett and the wild barley from Pakistan show the important role of apoplastic barriers as response to salt stress. The results indicate that wild barley of Pakistan accessions responds more strongly than the cultivar Scarlett in the event of salt stress of different intensities. Further investigations with more wild barley genotypes will improve our understanding of salt stress response and tolerance processes and can be used in future breeding programs to gain more salt tolerant crops.