The main objective of this project is to clarify how the activities of enzymes called apyrases exert dramatic effects on plant growth and development. Apyrases are enzymes that can hydrolyze various nucleotides, including ATP. Plants that are suppressed in their production of two apyrases, APY1 and APY2, are defective in their transport of the plant growth hormone auxin and are dwarf. The highest expression of these enzymes is in tissues that are rapidly growing. To better understand the implications of these findings, this project will investigate the molecular bases underlying them, using genetic, biochemical and cell biological approaches. APY1 and APY2 can function in the outer periphery of cells where they reduce the concentration of extracellular ATP. During cell growth some ATP made inside cells moves to the outside of cells where it acts as a hormone-like substance that influences many activities in plants, including cell expansion and the opening and closing of leaf pores called stomata. This project tests how the ability of apyrases to regulate the concentration of extracellular ATP relates to their ability to regulate plant cell size. New knowledge gained from the proposed experiments will deepen understanding about factors that control plant growth, and thus help develop new strategies for increasing crop yields and plant biomass for biofuels. The P.I. and co P.I. have a strong record of mentoring high school and undergraduate students in original research projects, and both are now principal instructors in the nationally lauded Freshman Research Initiative project on campus, which introduces large numbers of entering students to the challenge and joy of cutting-edge research. This activity is in accord with NSF's goal to foster integration of research and education through formal programs, and may serve as a model program for other such efforts in other Universities.