Water relations of lettuce. I. Internal physical aspects for two cultivars

Abstract

Experiments were performed to assess physical aspects of internal water relations (reported in this paper), and the gas exchange properties as affected by drought (reported in a second paper). A Dutch cultivar (‘Amanda Plus’) and a French cultivar (‘Sucrine’) were used. Water was withheld from plants for 5 or 9 days, and the latter group was rewatered to observe the pattern of recovery 1 day after rewatering. Measurements were made of plant water potential (hygrometry), sap osmotic potential (hygrometry and cryoscopy), sap electrical conductivity, and plant relative water content (RWC). Hygrometry was found suitable for measurement of plant water and sap osmotic potentials, although equilibration time for the former parameter was long. With suspension of irrigation, all the parameters decreased except for the electrical conductivity which increased. Leaf water and osmotic potentials were lower in ‘Amanda Plus’ than in ‘Sucrine’, but pressure potential in the former was better maintained. Significant parabolic regressions existed for RWC and osmotic potential on plant water potential. The significant linear regressions of plant water and sap osmotic potentials on sap electrical conductivity were thought to provide easy methods for measurements of the 2 former parameters.