Turgor maintenance, osmotic adjustment and soluble sugar and proline accumulation in 49 pea cultivars in response to water stress

The response of 49 pea cultivars with different drought tolerance was studied. The tolerance to stress was determined according to the grain yield or the harvest index in rainfed farming. In these conditions variability among the genotypes in turgor maintenance, measured as the slope of the turgor potential (Ψ(p)) function against water potential (Ψ(w)), was observed. The cultivars, which best maintained turgor, were those which were more drought-tolerant. Turgor maintenance was significantly related to osmotic adjustment (OA). However, OA does not explain all the variability observed in dΨ(p)/dΨ(w). Therefore, other factors such as tissue elasticity may also be influential. Soluble carbohydrate concentration increased (from 1.5 to 7 times) when the studied cultivars were subjected to water stress. The lines with a conventional leaf-type, showed a greater sugar content than semileafless lines when watered as well as when subjected to desiccation. The stimulation of sugar levels induced by drought was proportional to OA. During stress, the average soluble sugar content of all cultivars would be equivalent to 17.3% or 8.6% of Ψ(s)100, if all carbohydrates were present in the tissue as monosaccharides or disaccharides, respectively. This suggests that sugars play an important role in OA in peas. The free proline level also increased (from 4 to 40 times) in response to water stress. However, the contribution of this amino acid to Ψ(s)100 was small (approximately 1%) and no significant relationship was observed between proline content and OA. The cultivars which accumulated more proline had lower water contents upon turgor loss. This seems to indicate that proline may play a role in minimizing the damage caused by dehydration.