Vol.:(0123456789) 1 3 Journal of Plant Growth Regulation https://doi.org/10.1007/s00344-019-10048-5 Diferential Salt Sensitivity of Two Flax Cultivars Coincides with Diferential Sodium Accumulation, Biosynthesis of Osmolytes and Antioxidant Enzyme Activities Ahmad Mohammad M. Mekawy 1  · Dekoum V. M. Assaha 2  · Akihiro Ueda 2,3 Received: 8 June 2019 / Accepted: 25 October 2019 © Springer Science+Business Media, LLC, part of Springer Nature 2019 Abstract The present study was conducted in order to determine the response of two Egyptian fax cultivars (Sakha 102 and Sakha 105) to salt stress. To this end, seedlings of both cultivars were subjected to 150 mM NaCl condition, and the growth, Na + and K + concentrations, proline and hydrogen peroxide concentrations, and antioxidant enzyme activities were measured and compared with plants grown under non-stressed conditions. The results showed that salt stress reduced the overall growth of Sakha 102 by 38% as opposed to almost 50% reduction in Sakha 105. H 2 O 2 signifcantly increased in Sakha 105, but remained unchanged in Sakha 102. The Na + concentration in the leaf of Sakha 102 was 30% more than in the leaf of Sakha 105. The K + concentrations were reduced by the same degree in all tissues of both plants and the Na + /K + ratios were similar in both cultivars (generally > 1). The proline concentration was signifcantly more elevated in leaf, stem, and root of Sakha 102 (5.4, 2.5, and ten-fold, respectively) than in Sakha 105 (2.3, 2.3, and 4.0-folds). CAT activity markedly increased in the root of Sakha 102 (3.5-fold), but remained unchanged in Sakha 105. Taken together, these results suggest that Sakha 102 is more salt tolerant than Sakha 105, and that diferences in proline concentration and ROS production under stress may account to a greater degree in the diferential tolerance. Keywords Antioxidant enzymes · Flax · ROS scavenging · Proline · Salt tolerance Introduction High soil salt content is a factor limiting agricultural produc- tion in many regions (Yamaguchi and Blumwald 2005). In order to maximize the production potential of these regions, there is a need to develop crops tolerant to salinity. It is, therefore, important to understand the mechanisms of adap- tation of plants to salt stress. Since response to salt stress is multifactorial and there are cultivar-specifc variations, it is important to assess salt tolerance on a cultivar-by-cultivar basis (Assaha et al. 2017b; Chuamnakthong et al. 2019). Physiological and molecular analyses have deepened our understanding of the mode of responses and survival of plants tolerant to salt stress conditions. As soil solute potential and water conductance reduce across the root/ soil boundary (mainly due to increased Na + concentra- tion in soil solution), water uptake and translocation to the photosynthetic tissues are impeded. This decreased water availability often leads to stomatal closure and consequently reduced photosynthetic rate (Munns 2002; Ueda et al. 2003). In order to balance this soil solute potential to favor stable water fux, plants use photosynthates to synthesize and accu- mulate osmolytes or compatible solutes such as proline and glycine betaine (Türkan and Demiral 2009). This counter mechanism often comes at a huge cost, because it diverts resources that would have been used for growth, leading to drastic growth reduction. Another effect of salt stress in plants is ionic stress, mainly due to cellular infux of Na + (Munns 2002). The main efect of this infux is membrane depolarization, with a consequential activation of voltage-gated channels like GORK and NSCCs, which facilitate K + efux from the * Akihiro Ueda akiueda@hiroshima-u.ac.jp 1 Department of Botany and Microbiology, Faculty of Science, Minia University, El-Minia 61519, Egypt 2 Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima 739-8528, Japan 3 Graduate School of Integrated Sciences for Life, Hiroshima University, Higashi-Hiroshima 739-8528, Japan