Osmotic adjustment in tissues of tall fescue in response to water deficit

Understanding plant response to drought is important in evaluating mechanisms of drought tolerance. Osmotic adjustment was measured in various structures in the temperate grass tall fescue (Festuca arundinacea Schreb. cv. Kentucky 31) to characterize whole-plant response to water stress and to determine tissues most responsive to intermittent water deficit. A replicated greenhouse trial was conducted in which soil-grown tall fescue was watered or subjected to a series of drying cycles. Daily temperatures usually ranged from 20 to 32°C. Tissues sampled were youngest, fully expanded leaf blade, its sheath, emerged portion of expanding (immature) leaf blade, unemerged portion of same leaf blade, and all remaining basal tissue below the ligule inside the whorl. Plants osmotically adjusted (P < 0.05) by 0.08 MPa in fully expanded leaf blades, and by greater amounts in progressively younger tissues to 0.49 MPa in the basal meristematic and expanding region of unemerged leaves. Basal tissue exhibited the greatest osmotic adjustment relative to other tissues despite minimal declines in water potential and turgor during drying cycles, suggesting that water potential per se didnot regulate osmotic adjustment. Following overnight rehydration, the osmotically adjusted state persisted for 3-6 days in emerged immature blades, which was also reflected in increased turgor. Osmotic adjustment occurred in all types of tall fescue leaf tissue sampled, with increasing magnitude from oldest to youngest tissue, and younger tissue was more resistant to water deficit than older tissue. Results are discussed in relation to plant survival during periodic drought.