WATER DEFICIT EFFECTS ON OSMOTIC POTENTIAL, CELL-WALL ELASTICITY, ANDPROLINE IN 5 FORAGE GRASSES

Physiological responses of forage grasses to water deficit are not wel l documented, but may be important in determining drought resistance. The objective of this study was to determine the response of osmotic p otential, leaf proline concentration, and cell wall elasticity to wate r deficit for the C4 (warm-season) grasses 'Nebraska 54' indiangrass [ Sorghastrum nutans (L.) Nash], 'Pathfinder' switchgrass (Panicum virga tum L.), and 'Pawnee' big bluestem (Andropogon gerardii Vitman), and t he C, (cool-season) grasses, 'Ioreed' reed canarygrass (Phalaris arund inacea L.), and 'Lincoln' smooth bromegrass (Bromus inermis Leyss.). O ther measurements included leaf water potential, soil water content, a nd 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 adjustme nt, C3 grasses had more elastic cell walls (low modulus of cell wall e lasticity), which maintained turgor despite loss of water. Leaf prolin e concentration averaged 20 times greater in stressed compared to well -watered plants grown in the greenhouse. Proline accumulation in green house-grown plants was much larger than observed under field condition s. The physiological role of proline accumulation was uncertain becaus e even dramatic increases in leaf proline concentration were insuffici ent to influence osmotic potential.