Calcium ions and cytoskeleton contribute importantly to the process of pollen tube growth. A calcium gradient located at the tip of the pollen tube may control the fusion of incoming vesicles, while the microfilament cytoskeleton appears to move the vesicles to the tip. The proposed project will further explore the role these factors play in tip growth, and in addition examine the impact of calcium ion on the cytoskeleton and vice versa. Dr. Hepler will measure the gradient in free calcium ion using ratiometric fluorescent dyes that have been microinjected in single pollen tubes. He will determine the extracellular inward calcium current using a ion specific vibrating electrode. He will explore the detailed ultrastructure of the cytoskeleton in pollen tubes that have been prepared by rapid freeze fixation-freeze substitution. Finally, he will identify the cytoskeletal components at the electron microscope level using gold tagged antibodies. The above analytical methods when applied to cells cultured under experimental conditions that block elongation through perturbation of either the calcium ion gradient or cytoskeletal function may provide important new information about the control of growth and polarity in developing pollen tubes. %%% Understanding how the pollen tube of plants grows could have important impact on plant breeding in agriculture and horticulture.
