Sodium chloride enhances suberization in seminal roots but does not affect cutinized leaf barriers in cultivated and wild barley.

Abstract

Main conclusion: In the two compared barley genotypes, broader genetic variation did not result in a higher salt tolerance. Instead, specific traits like an exodermis might represent valuable future breeding targets. Soil salinification is a globally increasing phenomenon threatening agricultural yields. In this study, we investigated the physiological reactions of two genotypes of the fourth most abundant cereal crop barley in response to hydroponic sodium chloride exposure. It was of interest to compare a modern cultivar intentionally bred for the highest yields with a wild accession comprising a wider genetic background. Since barley is known to be a relatively salt-tolerant crop, three different sodium concentrations of up to 280 mM have been tested. The physiological adaptations of shoots and roots were investigated utilizing stomatal conductance measurements, chlorophyll fluorometry, morphometry, osmotic potential determination, mineral element concentration measurement, as well as histochemical and chemical analysis of apoplastic leaf and root barriers. While the leaf cuticle of both genotypes hardly reacted to the imposed stresses, the roots exhibited an increased endodermal suberization of especially the root tip, which strongly deviated from the previous findings about pure osmotic stress exposure. Interestingly, the putatively higher drought-tolerant wild accession did not show a considerably better growth performance, which in the context of sodium chloride stress might be attributed to its overall significantly smaller endodermal suberization reaction. We conclude that a subsequent study of a wild accession and/or a modern cultivar known to develop an exodermis might deliver valuable additional insights into potential future breeding targets. Such a suberized exodermis might be capable of conveying increased tolerance to toxic salts without negatively affecting water uptake.