Differential proteomic responses to water stress induced by PEG in two creeping bentgrass cultivars differing in stress tolerance.

Protein metabolism and expression play important role in plant adaptation to water stress. The objectives of this study were to examine proteomic responses to water stress induced by polyethylene glycol (PEG) in creeping bentgrass (Agrostis stolonifera L.) leaves and to identify proteins associated with stress tolerance. Plants of two cultivars ('Penncross' and 'Penn-A4') differing in water stress tolerance were grown in sand irrigated daily with water (control) or PEG solution (osmotic potential of -0.66MPa) to induce water stress, for 28d in growth chambers. Shoot extension rate, relative water content and cell membrane stability were measured to compare drought tolerance between the two cultivars. All parameters maintained at a significantly higher level in 'Penn-A4' than in 'Penncross' under PEG treatment. After 28d of water stress, proteins were extracted from leaves and separated by difference gel electrophoresis. Among 56 stress-responsive protein spots, 46 were identified using mass spectrometry. Some proteins involved in primary nitrogen and carbon metabolism were down-regulated by PEG-induced water stress in both cultivars. The abundance of antioxidant enzyme proteins (ascorbate peroxidase, catalase and glutathione-S-transferase) increased under water stress, particularly ascorbate peroxidase in 'Penn-A4'. The abundance levels of actins, UDP-sulfoquinovose synthase and glucan exohydrolase were greater in 'Penn-A4' than in 'Penncross' under PEG treatment. Our results suggest that proteins involved in membrane synthesis, cell wall loosening, cell turgor maintenance, and antioxidant defense may play roles in perennial grass adaptation to PEG-induced water stress.