RESUMEN
The response of onion tissue cultures to salinity stress was investigated. Callus initiated from aseptic seedlings was exposed to different levles of salt mixture. Fresh weight and growth value of callus inoculms were decreased as salt mixture increased in culture medium. However, dry weight and dry matter increased as salt level increased up to 4000 ppm and then decreased. Total proteins of callus enhanced as salt mixture increased in culture medium. For selection under salt stress, regenerated shoot buds derived from tolerant callus cultures were exposed to the different levels of salts mixture. The number of proliferated shoot buds and their fresh weight and growth value were depressed upon increasing of salts in medium. The best results of salt tolerance ratio were reached at 2000 ppm salts. Although protein content took similar trend of callus, it was relatively higher than in callus cultures at the same salt levels. Esterase patterns showed new band with the tolersnce lines. This band had different mobility and more intensity with the shoot bud lines exposed to 2000 ppm of salt mixture. The tolerant shoot buds were in vitro rooted and successfully adapted to free-living conditions