Contribution of Osmotic Adjustment to the Maintenance of Photosynthesis during Water Stress

Abstract

Water deficits develop in leaves of higher plants during drought, and as leaf water potential declines both cell volume and cell turgor fall. Osmotic adjustment is a process that helps maintain both turgor and volume as the deficits intensify. When turgor is maintained, processes that are influenced directly by turgor, such as stomatal conductance, assimilation rate and expansion growth are fully or partially maintained, and photosynthesis continues, albeit at a reduced rate. The carbon fixed can potentially contribute to: seed growth during the grain-filling period; shoot growth and competitive ability; root growth and extraction of soil water; and maintenance and survival of existing tissues. Consequently, the relationships between osmotic adjustment and maintenance of photosynthesis during water stress is of interest to the agriculturalist, as well as the ecophysiologist. Moreover, osmotic adjustment is already being used as a selection criterion to improve the yield of wheat in water limited-environments (1).