Effects of salt and osmotic shocks on unadapted and adapted callus lines of tobacco

Growth, viability and proline content of adapted and unadapted calluses of Nicotiana tabacum L. var. Jayasri, affected due to osmotic stresses and particularly to stress-shocks treated with different osmotica like NaCl (ionic-penetrating), mannitol (non-ionic-penetrating) and polyethylene glycol, (PEG) (non-ionic-non penetrating) were studied to evaluate the physiological differences of stress effects. The tissues adapted to a low concentration of NaCl (85 mM) showed low growth with high proline content compared to the tissues adapted to a low concentration of mannitol (165 mM). Proline content was similar in tissues adapted to high concentrations of NaCl (171 mM) and mannitol (329 mM) but growth in the latter case was relatively low. Growth and viability were subsequently correlated with the pattern of retention in or diffusion of proline out of the tissues after shock-treatments. The loss of tissue viability of the adapted calluses was comparatively less than the unadapted callus even after shock-treatments with 1282 mM NaCl and 823 mM mannitol. The former calluses retained the capability of regrowth though at a slow rate. Such adapted tissues also retained more proline. The mannitol-adapted tissues, when shocked with PEG (200 g l(-1)), showed low viability with more diffusion and a very little retention of proline while, in the unadapted tissue, all the proline was leached out. The results indicated that the effects of different osmotica on plant tissue varied depending upon the physico-chemical nature of the compounds used as stress-inducing-agents, and retention and diffusion of proline was altered when the tissues were shocked with high concentrations of all these compounds.