Analysis of Stress-Responsive Leaf Proteins in Kentucky Bluegrass Under Stresses of Drought or Heat Alone or in Combination.

Drought and heat are major limiting factors of plant production worldwide. The objective of this study was to investigate physiological and proteomic responses to drought and heat alone or together in two Kentucky bluegrass (Poa pratensis L.) cultivars. Plants of ‘Brilliant' and ‘Midnight' were subjected to drought stress (withholding water for 9 days) or heat (35 ^oC) or the combined stresses in growth chambers. Leaf relative water content (RWC) and photochemical efficiency (Fv/Fm) decreased under drought stress, while electrolyte leakage (EL) increased under heat or drought stress. The reduction in RWC and Fv/Fm and the increase in EL were more severe under combined heat and drought stress than under heat or drought stress alone. The reduction in RWC and Fv/Fm and the increase in EL were more severe in ‘Brilliant' than in ‘Midnight' under stresses. Leaf proteins were extracted and separated by two-dimensional gel electrophoresis. Approximately eighty protein spots were differentially accumulated in response to stress in at least one cultivar.  The sequences of these protein spots were analyzed using mass spectrometry and most of these spots were identified.  Many proteins involved in amino acid metabolism or energy metabolism were down-regulated under stress in both cultivars, and most of these proteins had higher level in ‘Midnight' than in ‘Brilliant' cultivar.