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Physiological responses of forage grasses to water deficit are not well documented, but may be important in determining drought resistance. The objective of this study was to determine the response of osmotic potential, leaf proline concentration, and cell wall elasticity to water deficit for the C4 (warm-season) grasses 'Nebraska 54' indiangrass [Sorghastrum nutans (L.) Nash], 'Pathfinder' switchgrass (Panicum virgutum L.), and 'Pawnee' big bluestem (Andropogon gerardii Vitman), and the C3 (cool-season) grasses, 'Ioreed' reed canarygrass (Phalaris arundinacea L.), and 'Lincoln' smooth bromegrass (Bromus inermis Leyss.). Other measurements included leaf water potential, soil water content, and osmotic adjustment. A field study at Mead, NE, and a complementary greenhouse study at the University of Nebraska, Lincoln, found osmotic adjustment occurred in response to water deficit for all species, and was greater for C4 than for C3 grasses. Despite less osmotic adjustment, C3 grasses had more elastic cell walls (low modulus of cell wall elasticity), which maintained turgor despite loss of water. Leaf proline concentration averaged 20 times greater in stressed compared to well-watered plants grown in the greenhouse. Proline accumulation in greenhouse-grown plants was much larger than observed under field conditions. The physiological role of proline accumulation was uncertain because even dramatic increases in leaf proline concentration were insufficient to influence osmotic potential.