Physiological and transcriptomic analysis of Hordeum jubatum seedlings in response to salt, alkali and drought stresses under uniform water potential

The early seedling stage is highly susceptible to various abiotic stresses. Hordeum jubatum is an ornamental plant with excellent abiotic stress tolerance, and widely distributed in the northeast of China. However, the mechanism of its physiological and transcriptional resistance under different abiotic stresses is still unclear. The results showed that the leaves of H. jubatum adapted to saline-alkali and drought environments by increasing the density of wax and glandular hairs, reducing the stomatal length, width and opening, and the leaf cells completely ruptured and a large number of organelles disintegrated under alkali stress. With the increasing stress concentration, the chlorophyll content and dry weight reduced under the three stresses, which was related to the broken chloroplasts of such conditions. In addition, the balance of Na+ and K+ was disturbed, and the increase of APX and SOD activity was the strategy to maintain the balance of reactive oxygen species and weaken the degree of membrane lipid peroxidation under three stresses. And alkali stress had the most significant effect on above changes. Moreover, Transcriptional sequencing revealed the alkali stress group had the highest number of differential expressed genes (DEGs) compared to the CK among three stresses, and a significant down-regulation of DEGs related to membrane systems under three stresses. In addition, alkali stress resulted in large number of up-regulation of DEGs associated with light repair processes and down-regulation of DEGs in ribosomal pathway with R proteins involving in regulating leaf phenotype and ultrastructure, which also echoed the overall physiological findings. Together, the adaptation mechanisms of three stresses were different in H. jubatum seedlings with higher tolerance of salt stress, and extremely sensibility to alkali stress.