Comparative Analysis of Drought Responsive Proteins in Kentucky Bluegrass Cultivars Contrasting in Drought Tolerance

Knowledge of drought-responsive proteins is critical for further understanding of molecular mechanisms of drought tolerance. The objective of this study was to identify drought-responsive proteins associated with drought tolerance in Kentucky bluegrass (Poa pratensis L.) by comparing proteomic responses to drought stress in two cultivars differing in drought tolerance. Plants of drought-tolerant 'Midnight' and drought-sensitive 'Brilliant' were subjected to drought stress by withholding irrigation for 15 d in growth chambers. Midnight maintained significantly higher relative water content and photochemical efficiency and lower membrane leakage than Brilliant under drought stress. Difference gel electrophoresis and mass spectrometry analyses detected 88 drought-responsive proteins in both cultivars. Many proteins involved in amino acid or energy metabolism were downregulated under drought stress in both cultivars, but most of those proteins had higher abundance in Midnight than in Brilliant. Several heat shock proteins and chaperons exhibited differential accumulation between the two cultivars, with an increase in the abundance of 70 kDa proteins in Midnight and decreases of 60 kDa chaperonin and FtsH proteins in Brilliant under drought stress. The differential accumulation of those proteins involved in amino acid and energy metabolism, as well as for protein chaperons, could be associated with drought tolerance in Kentucky bluegrass.