Elevated Cytokinin Content In Creeping Bentgrass May Promote Drought Tolerance by Regulation of the Metabolite Profile.

Increased endogenous plant cytokinin (CK) content through transformation with an isopentyl transferase (ipt) gene has been found to be an effective method to promote plant drought tolerance. This study aimed to analyze the effects of differential CK content on the accumulation of major leaf metabolites in creeping bentgrass (Agrostis stolonifera L.) exposed to drought stress. Null transformant (NT) and transgenic plants transformed with ipt controlled by a senescence activated promoter (SAG12-ipt) were exposed to drought stress in an environmental growth chamber until the moisture content of the 1:1 sand:soil growing mix reached approximately 5%. A metabolite profile consisting of 45 distinguishable metabolites were identified and categorized as amino acids, carbohydrates, organic acids, and organic alcohols. The enhanced drought tolerance of SAG12-ipt plants may be related to the maintenance of several important metabolites, particularly the amino acids: proline, γ-aminobutyric acid, alanine, and glycine and carbohydrates: sucrose, fructose, maltose, and ribose. SAG12-ipt plants also exhibited differential regulation of several important organic acids, particularly those involved in the citric acid cycle. Specific metabolite changes identified over the course of drought stress and at the same level of leaf relative water content (47% RWC) in NT compared to SAG12-ipt plants are discussed, which may be particularly important to understanding the involvement of CK in the drought response.