Plant growth alterations in halophyte Prosopis strombulifera (Lam.) Benth. and natrophile Glicyne max (L.) Merril in response to salinity and changes in auxin transport

Abstract

The effects of changes in auxin transport in response to different osmotic potentials (Ψo) were analyzed in the roots and leaves of two leguminous species with different degrees of salt tolerance: the halophyte Prosopis strombulifera (Lam.) Benth. and the glycophyte Glycine max L. The potentials were generated with sodium chloride (NaCl), sodium sulfate (Na2SO4), and the iso-osmotic mixture of both salts (NaCl + Na2SO4). The values evaluated were −1, −1.8, and −2.6 MPa for P. strombulifera, and −0.47, −0.69, and −0.87 MPa for G. max. In addition, the plants were sprayed with 2,3,5-triiodobenzoic acid (TIBA), an auxin transport inhibitor. The parameters measured included root length, shoot height, number of leaves, relative membrane permeability in roots, and endogenous levels of abscisic acid (ABA), indole-3-acetic acid (IAA), and zeatin (Z). Significant responses were observed at the lowest potentials evaluated (−2.6 MPa for P. strombulifera and −0.89 MPa for G. max). Treatment with Na2SO4 inhibited plant growth more than the others, increased the relative membrane permeability, and enhanced ABA production to its highest levels. These toxic effects were slightly reversed in the presence of iso-osmotic mixture. TIBA brought about impaired development in shoots and roots, the highest values for membrane permeability, alterations in the distribution of endogenous ABA, IAA, and Z, as well as harmful effects on the growth response of both species. In general, the alterations in auxin transport intensified the effects of salinity, which confirms the essential role of this mechanism in plants under salt stress or in normal, non-stressful conditions.