Selection of callus cultures of sugarcane (Saccharum sp.) tolerant to NaCl and their response to salt stress

Stable callus cultures tolerant to NaCl (68 mM) were developed from salt-sensitive sugarcane cultivar CP65-357 by in vitro selection process. The accumulation of both inorganic (Na+, Cl- and K+) and organic (proline and soluble sugars) solutes was determined in selected and non-selected calli after a NaCl shock in order to evaluate their implication in in vitro salt tolerance of the selected lines. Both salt-tolerant and non-selected calli showed similar relative fresh weight growth in the absence of NaCl. No growth reduction was observed in salt-tolerant calli while a significant reduction about 32% was observed in nonselected ones when both were cultivated on 68 mM NaCl. Accumulation of Na+ was similar in both salt-tolerant and non-selected calli in the presence of NaCl. Accumulation of Cl- was lower in NaCl-tolerant than in non-selected calli while proline and soluble sugars were more accumulated in salt-tolerant than in non-selected calli when both were exposed to salt. K+ level decreased more severely in non-selected calli than in NaCl-tolerant ones after NaCl shock. The results indicated that K+ and Cl- may play a key role in in vitro salt-tolerance in sugarcance cell lines obtained by in vitro selection and that organic solutes could contribute mainly to counteract the negative water potential of the outside medium.