Photosynthetic enzyme activities and gene expression associated with drought tolerance and post-drought recovery in Kentucky bluegrass

► We investigated photosynthetic enzymes for drought tolerance in a grass species. ► Carbon fixation and reduction were key processes imparting drought tolerance. ► Resumption of active carbon fixation was a key factor for post-drought recovery. Maintaining active photosynthesis is important for plant adaptation to drought stress. The objective of this study was to determine major photosynthetic factors associated with genetic variability governing drought tolerance and post-drought recuperative ability of a perennial grass species, Kentucky bluegrass (Poa pratensis), by examining differential photosynthetic responses and underlying enzyme activities as well as gene expression during drought stress and re-watering for two cultivars contrasting in drought tolerance. Plants of two cultivars (‘Midnight’ and ‘Brilliant’) were exposed to 10d drought stress and subsequently re-watered for 3d in growth chambers. Physiological analysis via turf quality, relative water content, and electrolyte leakage confirmed that ‘Midnight’ exhibits superior drought tolerance and post-drought recuperative ability. Drought-tolerant ‘Midnight’ maintained significantly higher net photosynthetic rate (Pn), higher enzymatic activity and transcript level of ribulose-1,5-bisphosphate carboxylase (Rubisco), higher enzymatic activity of glyceraldehyde phosphate dehydrogenase (GADPH) during 10-d drought stress and in responses to re-watering, as well as higher Rubisco activation state upon re-watering. The two cultivars did not differ with regard to enzymatic activity or gene transcript level of phosphoribulokinase during drought stress or upon re-watering. These results suggest that carboxylation controlled by Rubisco and carbon reduction regulated by GAPDH could be the key metabolic processes imparting genetic variation in Pn responses to drought stress while active Rubisco, GAPDH and Rubisco activase could all be involved in the superior post-drought recovery in Kentucky bluegrass.