Physiological and Metabolic Factors Associated with the Improvement of Drought Tolerance in Creeping Bentgrass (Agrostis stolonifera L.) Expressing SAG12-Ipt Gene Controlling Cytokinin Synthesis.

Increased production of endogenous cytokinins (CKs) has been associated with whole-plant drought tolerance.  The goal of this study was to evaluate physiological and metabolic mechanisms of improved drought tolerance in creeping bentgrass (Agrostis stolonifera L. ‘Penncross’) expressing the ipt-gene encoding isopentenyl phosophotransferase linked to a senescence associated promoter (SAG12) for CK synthesis.  Tillers of SAG12-ipt and wild-type (wt) were planted into bins (42x52x30 cm) filled with fritted clay and allowed to establish for seven-weeks prior to water withholding.  Irrigation was withheld for 21 d, during which time plants were evaluated weekly for photosynthetic rate and efficiency, water relations, membrane stability, chlorophyll content, and visual turf quality.  Plants were destructively sampled at 21 d (8% SWC) to measure root and shoot biomass accumulation as well as membrane stability of root tissue.  As soil moisture declined to critical levels, SAG12-ipt plants maintained higher photosynthetic rates correlating to increased chlorophyll content as well as maintenance of cellular membranes and photosynthetic machinery.  Significantly better quality ratings for SAG12-ipt plants were also linked to improvement of whole-plant water relations seen by increased water content in leaf tissue as well as higher stomatal conductance and transpiration promoting canopy cooling.  SAG12-ipt plants had greater amounts of root biomass and significantly lower membrane leakage in root tissue compared to wt plants.  Little difference in shoot biomass was seen indicating SAG12-ipt plants allocated more resources to promote root growth and water uptake during drought.  Further analysis of root and shoot samples will be performed such as protein and hormone identification and quantification to investigate biochemical aspects associated with enhanced drought tolerance.