In vitro selection and physiological characterization of NaCl- and mannitol-adapted callus lines in Brassica juncea

Abstract

Na Cl (salt)- and mannitol (drought)- tolerant callue lines of Brassica juncea (L) Czern. Var. RW-85-59 were isolated by a plated cell suspension culture technique against 43 mM NaCl and 165 mM mannitol, respectively. Callus lines, adapted to a high concentration of Na Cl (171 mM) and mannitol (329 mM) were then established bv direct adaptation procedures. In the initial passages, the calluses showed severe reduction in tissue growth when grown on NaCl/mannitol-containing media but growth of adapted calluses recovered and was sustainable in the subsequent passages. Adapted calluses showed considerable accumulation of free proline in NaCl-/mannitol- containing media compared to the control callus grown on stress-free medium. A significant increase of intensity of one particular acid phosphatase isozymic band in the adapted calluses, irrespective of NaCl or mannitol stress, indicated that it may be used as an osmotic stress-marker in this system. Short-term salt/osmotic-shock-treatment with high concentrations of osmotica revealed that only the adapted lines retained the maximum amount of free proline within the cells for osmoregulation. This response probably helped the cells to restore their normal growth when the stress was withdrawn.