Physiological Changes after Exposure to and Recovery from Polyethylene Glycol-induced Water Deficit in Callus Cultures Issued from Durum Wheat (Triticum durum Desf.) Cultivars Differing in Drought Resistance

Calli obtained from three durum wheat (Triticum durum Desf.) cultivars with different drought resistance levels were exposed for 30 days to a polyethylene glycol-induced water deficit followed by 30 days of recovery. Relative growth rate, percent dry weight, osmotic potential and the changes in inorganic and organic solutes were determined at the end of both the stress and the recovery periods. After the stress period, calli derived from the drought resistant cultivars, particularly Omrabi 5 and to some extent Haurani, showed a less reduced relative growth rate, lower osmotic potential and higher proline and other amino acid accumulations as compared with the sensitive cultivar Kabir 1. Drought resistance could also be associated with a better protection of enzymes involved in nitrogen metabolism. At the end of the recovery period, most of the quantified parameters, except osmotic potential, recovered completely, indicating the reversibility of the changes induced by water deficit at the plant cell level in durum wheat. Our data show that a correlation exists between performances of the cultivars under drought and the responses of callus cultures to PEG-induced water deficit; this suggests that in durum wheat the degree of resistance to drought at the plant level depends, at least in part, on the existence of mechanisms operating at the cellular level.