The role of organic solutes in dehydration tolerance of several Populus deltoides clones

Some of the solutes (e.g. sugars) that contribute to osmotic adjustment in water stress acclimated plants may be involved in cell membrane-stability. The objective of this study was to determine the relationships between osmotic potential, organic solutes, and cell membrane-stability (as measured by electrolyte leakage). The effects of water stress preconditioning on osmotic adjustment, cell membrane-stability, and gas-exchange were investigated in three greenhouse-grown Populus deltoides Bartr. clones: Ohio Red (from southern Ohio), Platte (from eastern Nebraska), and Wildcat (from western Nebraska). Gas-exchange measurements of Ohio Red and Platte showed differences in recovery, with photosynthesis of Ohio Red recovering fully from a severe stress ($-$1.05 MPa) on the second day of rewatering while Platte did not recover (71%) by the fourth day. Platte and Wildcat maintained high leaf water potentials which may be related to their low stomatal conductance and fewer stomata than Ohio Red. All clones showed osmotic adjustments ranging from 0.18 to 0.52 MPa with organic solutes accounting for up to 50% of osmotic adjustment and no accumulation of inorganic ions. The concentration of each water-soluble organic solute was greater in samples collected in the summer (July) than in the winter (January) indicating a possible effect of photoperiod on organic solute concentration and osmotic adjustment. There were clonal differences in the type of solutes accumulated, with Ohio Red accumulating the most sucrose of all clones and Platte and Wildcat accumulating more glucose, fructose, and salicin than Ohio Red. Rewatering of plants before sampling (to compare clones at full turgor) did not increase sucrose concentration in any of the clones, instead there was a decline in most solutes. Ohio Red showed the most cell membrane-stability which was correlated to the sucrose level. It is concluded that clones differed in solute accumulation and water-stress resistance characteristics, with Ohio Red showing more dehydration tolerance characteristics and the clones from Nebraska showing more dehydration postponement characteristics