PHYSIOLOGIA PLANTARUM 90: 408-^13. 1994 c.pyngh, ©pfci.<,,.fo«,,, !'ianu,n,m ISSN (K)M-9.u7 Prinieti in Denntark - al! rt,£,'/ii'.v rcsen-ej The relative contribution of elastic and osmotic adjustments to turgor maintenance of woody species Shihe Fan., Terence J. Blake and Eduardo Blumwald Fan. S.. Blake, T.J. and Blumwald. E. 1994. The relative contribution of elastic and osmotic adjustments to turgor maintenance of woody species. - Physiol. Plant. 90; 408-413. To determine how tissue water relations vary and contribute to turgor maintenance in species from contrasting ecological zones, seedlings of jack pine {Pinus banksiana Lamb.), black .spruce iPicea mariana |Mill) B.S.P.I and flooded gum (Eucalyptus grandis W. Hilt ex Maiden) were subjected to an 8 day drought stress by water withholding with and without prior mild water stress conditioning. Jack pine, a deep-rooted species from dry, sandy boreal sites, lost turgor at the low est relative water content (75-659^) and water potential, and had lowest maximum bulk elastic mtxlulus te^.,, of 5.2-5.S MPa). Although this suggests a high inherent dehydration tolerance, jack pine did not further adjust its elasticity when repeatedly stressed. Black spruce, a shallow-rooted species from predominantly moist sites in the boreal region, lost turgor at intermediate relative water content (86^769!) and water potential, but could adjust its elasticity to maintain turgor in repeatedly stressed tissues. Flooded gum, a deep- rooted species from moist, warm temperate-subtropical regions, had a low inherenl drought tolerance since it lost turgor a! higher relative water content (88-849r) and water potential, but was capable of some adjustment when the stress was repeated. Elastic adjustment (<3.7 MPa) was more important for turgor maintenance than osmotic adjustment (<0.i3 MPa). which was statistically nonsignificanE. Maximum bulk modulus of elasticity, but not o.smotic potentials at full turgor, was significantly correlated with the relative water content and water potential at zero turgor in droughted seedlings. These results highlight the importance of tissue shrinkage for dehydration tolerance. Both the inherent capacity for turgor maintenance of a spKcies under drought and its ability to adjust to repeated drought .should be considered in genetic selections for drought tolerance. Kev words - Black spruce, drought tolerance, elastic adjustment. Eucalyptus grandis, flooded gum, jack pine, osmotic adjustment, Picea mariana, Pinus banksiana, pres- sure-volume analysis, tissue water relations. S. fan. T. J. Blake (corresponding author) and E. Blumwald, Centre for Plant Biotech- nology, Faculty of Forestry, Univ. of Toronto. Toronto, Canada M5S 3BJ. , . . ., justment, the active accumulation of solutes in cells. Introduction , . ... ,, , lowers osmotic potential in cells and promotes water Turgor is critical to plant life since its loss inhibits growth absorption. Elastic adjustment results from modifications (Hsiao 1973). Loss of turgor triggers physiological and in the cell walls which make them more elastic, thereby biochemical adjustments that are important for turgor facilitating tissue shrinkage during dehydration (Blake maintetiance, and the likely importance of osmotic and and Tschaplinski 1992). elastic adjustments have been highlighted (Schulte 1992). Knowledge is lacking on the relative importance of Both elastic and osmotic adjustments help to maintain these tissue water relation parameters for turgor mainte- turgor at lower tissue water potentials and prevent me- nance in different types of trees. Osmotic adjustment chanical damages to plasma membranes. Osmotic ad- could help to explain genetic differences in drought to- Reeeived 23 March, 1993; revised 24 September, 1993 408 Physio!. Plara. WI. 19')4