Salinity and water stress have contrasting effects on the relationship between growth and cell viability during and after stress exposure in durum wheat callus

Mature embryo-derived calli obtained from three cultivars (cvs.) (Omrabi: drought-resistant; Belikh: salt-resistant; Cando: drought- and salt-sensitive) were exposed for one month to various iso-osmotic concentrations of NaCl, mannitol or polyethylene glycol (PEG) 6000. The lowest relative growth rate (RGR) for all cultivars, were observed in the presence of PEG. Correlation between RGR and cell viability estimated by reduction of 2,3,5-triphenytetrazolium chloride (TTC) was significant in the case of salt stress only. NaCl increased the relative importance of the non-phosphorylating alternative respiratory pathway while osmotic stress in contrast increased the relative importance of the CN-sensitive pathway. Neither mineral concentration, nor proline, nor soluble sugar accumulation fully accounted for lowering the internal osmotic potential in PEG-treated calli. Calli exposed to PEG were able to recover while those treated with mannitol were not. After NaCl treatment, only calli obtained from the salt-resistant cultivar Belikh recovered. It is concluded that (i) salinity and water stress have contrasting effects on the relationships between growth and cell viability, (ii) these relationships are not the same during and after the stress treatment, and (iii) maintenance of growth potential after the stress relief is linked to the maintenance of ATP-producing respiratory pathway rather than to a stress-induced stimulation of the alternative pathway. (C) 2004 Elsevier Ireland Ltd. All rights reserved.