The effects of extracellular ATP on growth in Arabidopsis thaliana
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Exciting contributions to the field of plant biology have challenged traditional views of and modes of signaling molecule action and activities. In addition to startling and widely touted discoveries such as F-box protein auxin receptors and endomembrane ethylene receptors, evidence has accumulated indicating that ATP may possess a non-canonical function external to the plant cell as a signaling agent. Recent publications have detailed the presence of extracellular ATP at the growing end of root tips, extracellular ATP-induce fluxes in cytosolic calcium, and the effects of extracellular ATP upon root growth and pollen tube elongation. Within these pages, I present evidence for concentration-dependent effects of extracellular ATP upon etiolated hypocotyl elongation and gene expression changes. These findings prompted us to measure the ATP concentration in wound serum of WT and mutant plants that produce an NTDPase, or apyrase (atAPYOE) protein in greater abundance than WT, and we found that the ATP concentration in wound serum derived from the atAPYOE mutants is lower than WT. I also report that apyrase protein levels decrease following exposure to red light, that it is present on the plasma membrane, and the active site likely faces the extracellular matrix. Finally, I describe my attempts to directly label a putative ATP-receptor protein predicted to reside on the external face of the plasma membrane. I have labeled a small number of plasma membrane proteins using a photoactive, radioactive ATP-derivative. As described more fully in the text, the predicted sequence of the labeled proteins was generated using mass-spec fingerprinting. In sum, I present novel data that contributes to our understanding of how plants and the plant cell perceive and respond to the external environment.