Growth responses to sulfate and chloride are related to different phytohormone profiles in the halophyte Prosopis strombulifera

Abstract

In this study, the profile of plant phytohormones traditionally considered as plant growth promoters (GA1, GA3, GA4, IAA and Z) was determined in roots and leaves of the halophyte Prosopis strombulifera grown hydroponically in iso-osmotic solutions of NaCl, Na2SO4 and their mixture. Hormonal levels were correlated with growth parameters and ABA levels. Different sodium salts in the medium differentially affected the synthesis of these compounds. NaCl treated plants showed the greatest accumulation of GA4 and GA1 and lower levels of their metabolites GA8 and GA34 both in root and leaves, in coincidence with the optimum growth observed at ?o -1.9 Mpa this response was also observed at ?o -2.6 MPa. IAA level was unaltered in these plants while Z content was higher in roots than in leaves. In contrast, both leaves and roots from Na2SO4 treated plants showed lower GA1 and GA4 and increased GA8 and GA34 levels at high salinity. High levels of IAA were found in roots of these plants, but the ABA/IAA ratio increased with increasing salt concentrations in the culture medium. This pattern was also observed in the high ABA/GAs ratios. Z levels were very low in all salt treatments. The results of this study show that the halophytic growth under NaCl treatment is mainly regulated by GA1 and GA4 and low relative levels of ABA and IAA. The toxicity of sulfate alters this pattern reversing the ratio ABA/GAs and increasing the synthesis of IAA in conjunction with increased lateral root formation. In bisaline-treated plants intermediate values were observed in the levels of these phytohormones as compared to monosaline treatment.