Mechanism Involved In Drought Response And Post-drought Recovery In Kentucky Bluegrass (Poa Pratensis L.)

Kentucky bluegrass (Poa pratensis L.) is one of the most popular turfgrass species in China. Drought stress is one of the most detrimental limiting factors for turfgrass growth and turf quality. Drought damage is characterized by leaf dehydration and senescence during mild and moderate stress and desiccation under severe conditions. Therefore, to understand the mechanism of drought tolerance and post-drought recuperative ability is very import for breeding drought tolerant cultivars.Two cultivars of Kentucky bluegrass, drought tolerant'Midnight'and drought sensitive'Brilliant' were used to investigate the different cultivar responses particularly photosynthesis rate responses. Also factors may affect the cultivar difference on photosynthesis rate were tested:key enzymes involved in calvin cycle of photosynthesis; membrane fatty acids changes which affect (thylakoid) membrane fluidity; changes of antioxidant enzyme both at enzymatic activity and gene expression levels and other important proteins such as aquaporin, heat shock proteins and so on.Results showed that, compared to'Brilliant','Midnight'is more drought tolerant.'Midnight' maintained higher turf quality, leaf photochemical efficiency, relative water content, and membrane stability expressed as electrolyte leakage during drought stress. Following re-watering,'Midnight' recovered more rapidly in each parameter than'Brilliant'. During drought treatment,'Midnight'was able to maintain significantly higher level of photosynthesis rate although under well-watered conditions 'Midnight'was significantly lower in photosynthesis rate compared to'Brilliant'. The higher photosynthesis rate in'Midnight'during drought stress was not due to higher stomatal conductance but metabolic reasons such as initial and total activity of Rubisco. The degree of fatty acid unsaturation decreased in both cultivars during drought stress, and the decrease was less pronounced and occurred later in'Midnight'. Moreover, enzymes involved in the ascorbate-glutathine cycle may play important roles in antioxidant protection to drought damage whereas CAT, POD, and APX could be associated with better post-drought recovery in Kentucky bluegrass. Leaf dehydration tolerance and post-drought recovery in Kentucky bluegrass was associated with their ability to maintain higher level of photosynthesis rate, relative higher proportion and level of unsaturated fatty acids, particularly linolenic acids and linoleic acids and higher level of antioxidant enzyme activities such as activities of APX, MR, DR, and GR during severe drought stress.'Midnight' was able to maintain relatively higher proportion of unsaturated fatty acids and antioxidant enzyme activities which may be related to better membrane (thylakoid membrane) fluidity, stability and integrity and better properties of membranes was associated with higher photosynthesis rate during drought and better drought tolerance.