Salt-induced changes in the vegetative anatomy of Prosopis strombulifera (Leguminosae)

Seedlings of Prosopis strombulifera (Lam.) Benth. were grown hydroponically in Hoagland's solution with addition of 25 mmol/L NaCl every 48 h until final salt concentrations of 250, 500, and 700 mmol/L were reached. Control plants were grown without salt. Salinity induced anatomical changes in roots (young and mature zones), hypocotyls, young stems, and leaflets. The diameters of the young zone of roots of plants grown in increasing salt concentrations were smaller than those of controls, with reduced number of cortex layers and reduced size of the vascular system. The roots from tolerant plants showed precocious suberization and (or) lignification of the endodermal cells and early activity of the pericycle. Hypocotyl diameter was reduced along with a reduction in secondary phloem. Roots and hypocotyls showed abundant phellem formation. The stem diameter of young tolerant plants was notably diminished and less tissue lignification occurred. In stems and leaflets of treated plants, NaCl stimulated the production of tannins. In the leaflets, vascular bundles were similar in size. Groups of elongated parenchyma cells with many chloro plasts surrounded the bundles. These results suggest that in the absence of secretory organs, the anatomical modifications in this species are related to metabolic adaptations, such as an early development of the endodermal barrier for ion exclusion, to allow survival in high salinity.