Comparative Analysis of Proteomic Responses to Single and Simultaneous Drought and Heat Stress for Two Kentucky Bluegrass Cultivars

Protein metabolism may vary in response to drought, heat, or heat and drought stress combined. The variations in the abundance of different proteins may differentially affect adaptation mechanisms of plants to these three types of stresses. The objectives of this study were to examine differential protein responses and identify stress-responsive proteins associated with tolerance to drought, heat, or the combined stress in a perennial grass species. Plants of two cultivars of Kentucky bluegrass (Poa pratensis L.) contrasting in heat and drought tolerance (tolerant 'Midnight' and sensitive 'Brilliant') were treated with heat, drought, or a combination of the stresses in growth chambers. Physiological analysis demonstrated that Midnight maintained higher relative water content and photochemical efficiency and lower electrolyte leakage than Brilliant under all three stress treatments. Two-dimensional electrophoresis and mass spectrometry analysis identified some common proteins responsive to drought, heat, and the combined stress. Induction of a chaperonin and heat shock proteins (HSPs) 70 and 90) and downregulation of proteins involved in photorespiration occurred under all three stresses. The two cultivars exhibited differential accumulation of proteins involved in photorespiration, cell wall loosening, antioxidant defense, and photosynthesis, and therefore these proteins could be associated with the contrasting drought tolerance characteristics of the cultivars. The results also suggest proteins involved in membrane stability, ribonucleic acid (RNA) stability, cell wall loosening, and antioxidant defense could contribute to superior heat tolerance of Midnight. Proteins involved in photorespiration and those that are associated with photosystems may play a major role in Kentucky bluegrass tolerance to combined heat and drought stress.