Wednesday, November 15, 2006

Dehydrin Expression in Drought-Stressed Tall Fescue can be Modulated by Endophyte Presence.

Chuck West1, Claudia Guerber1, Rachel Carson2, and Dave Brauer3. (1) University of Arkansas, 1366 W Altheimer Drive, Crop Soil Environ Sci Dept, Fayetteville, AR 72704-6898, (2) University of Toronto, Botany Dept, Toronto, ON M5S 3B2, Canada, (3) USDA-ARS, Dale Bumpers Small Farm Research Center, Booneville, AR 72927

Summer drought stress limits persistence of tall fescue in the southern U.S. Its widely occurring endophyte, Neotyphodium coenophialum, promotes host drought tolerance; however, the physiological mechanisms of this effect are not well understood. Identifying biochemical or molecular markers for enhanced drought tolerance would facilitate the screening of beneficial endophytes for inoculation into improved tall fescue cultivars. Dehydrin protein expression occurs in many plants in association with dehydrating tissues, ostensibly maintaining membrane integrity during quiescent periods. Our objective was to determine whether the endophyte promotes dehydrin expression in elongating leaf tissue of vegetative tall fescue tillers during the onset of drought stress in genotypes whose native endophytes have been shown to enhance host drought survival. Endophyte-infected (E+) and endophyte-free (E-) clones of two genotypes, 60 and 330, were grown in a loamy fine sand in dishpans in a greenhouse. The pans were either allowed to dry or were maintained as watered controls. Plants were sampled by excising 2-cm tiller bases from several tillers, including the sheath of the youngest fully expanded leaf, at Stage 1 (onset of leaf blade rolling), Stage 2 (onset of leaf tip desiccation), and Stage 3 (immature leaf blade desiccated). Proteins reacting with DHN-4 primary antibody were detected by western blot. No dehydrin was expressed in any of the watered controls. Both genotypes exhibited heavier bands as severity of stress progressed. Genotype 60 expressed more numerous and heavier bands in E+ than in E- clones, indicating that endophyte presence stimulated dehydrin expression in response to drought. The banding pattern and intensity was not affected by endophyte in genotype 330. The fact that both genotypes have shown enhanced drought survival due to endophyte in previous trials, suggests that dehydrin accumulation is not universally associated with endophyte-enhanced drought survival across tall fescue genotypes.