Metabolomic Responses of Transgenic Creeping Bentgrass Overproducing Cytokinins to Heat Stress.

Leaf yellowing and reduced plant density are major problems associated with heat stress injury in cool-season turfgrasses. Our previous research indicates that high temperatures reduce the production of cytokinins, the hormone that controls leaf senescence, tillering and root formation, which are the principal physiological processes underlying this problem. We created two types of transgenic creeping bentgrass with a bacterial gene (ipt) encoding the enzyme adenine isopentenyl phosphotransferase. The ipt gene was ligated to two stress- activated promoters, SAG12 promoter from Arabidopsis that is activated at the start of leaf senescence and HSP18 heat shock promoter that is activated by exposing the plants to temperatures above 35 C. The objectives of this project are 1) to compare the changes in major metabolites between non-ipt control and two ipt-transgenic lines under heat stress, and 2) to determine whether the variance of heat tolerance between them was due to differential metabolic responses. Plants of each line were exposed to 20 (control) or 35°C (heat stress) for 2 (short-term) or 10 d (long-term) in growth chambers. Heat stress injury was evaluated by photochemical efficiency and chlorophyll content. The type and content of polar metabolites in shoot and root samples were analyzed using GC/MS. Our results indicated that differential responses of transgenic and non-transgenic plants to heat stress mainly exhibited in the metabolism of amino acids, organic acids and carbohydrates. Overproduced cytokinins may improve heat tolerance of the ipt-transgenic creeping bentgrass by up-regulating the production of certain essential amino acids, organic acid and carbohydrates.