Inhibition of root growth by alkaline salts due to disturbed ion transport and accumulation in Leymus chinensis

Abstract

Soil alkalization severely affects plant growth and agricultural production. Compared with neutral salts, alkaline salts cause a combined stress of ion toxicity and high pH in plants. The alkali-resistant halophyte Leymus chinensis is a dominant grass growing on soda (NaHCO3 and Na2CO3, pH > 9) saline-alkali soil in northeast China. However, the molecular mechanism of alkaline salt tolerance in L. chinensis roots remains unclear. In this study, the seedling phenotype, ion accumulation, root ion dynamics, and gene expression profiles in L. chinensis under neutral salt (100 mM NaCl), alkaline salt (100 mM NaHCO3 and 50 mM Na2CO3), and high pH (pH = 10) stresses were investigated and compared. Phenotypic analysis showed that alkaline salt more severely inhibited the growth of seedling roots compared to neutral salt and high pH. Ion content detection revealed that alkaline salt-treated seedlings had higher Na+ accumulation and lower nutrient content compared to neutral salt and high pH-treated seedlings. Furthermore, the non-invasive micro-test showed that alkaline salt-induced high pH conditions perturb ion flux in seedling roots, which may be associated with impaired nutrient ion uptake and aggravated Na+ accumulation. Moreover, using full-length transcriptome combined with comparative RNA-seq, the identified alkaline salt-specific response genes were most significantly enriched to the transporter activity term, which contained a large number of genes encoding transporters of nutrient ions. Our results provide new insights into the unique response mechanism of L. chinensis roots to alkaline salt.