Stylosanthes, a genus of tropical forage legume, is known to exhibit good persistence in saline soils,
yet mechanisms for regulation of seed germination under salt stress are poorly understood. This study
was carried out to evaluate the mode of action of salt stress on seed germination of Stylosanthes. 1-
Aminocyclopropane-1-carboxylic acid (ACC) increased ethylene biosynthesis and germination of NaClinhibited
seeds in a dose-dependent manner. Contents of ACC and germination of Stylosanthes humilis
seeds increased following transfer from NaCl solution to deionised water, but not after transfer to l--(2-
aminoethoxyvinyl)-glycine (AVG) solution, an inhibitor of ethylene biosynthesis. Ethylene biosynthesis
wasmuchlarger inNaCl-treatedseeds of Stylosanthes guianensis thaninseeds of S. humilis andStylosanthes
capitata, a fact which was reflected in higher germination rates. S. guianensis seedlings also displayed
higher growth and survival rates than S. humilis and S. capitata under salt stress. Moreover, smaller
ACC levels, as well as reduced ethylene biosynthesis of S. capitata seeds were accompanied by lower
germination under salt stress. In addition, S. capitata seedlings treated with NaCl solutions exhibited
relatively lower growth and survival rates in comparison with S. humilis and S. guianensis. Thus, different
abilities to synthesize ethylene by S. guianensis, S. humilis and S. capitata seeds explain the differences in
tolerance to salt stress of the three species.