| Peter K. Hepler
Professor Emeritus of Biology, University of Massachusetts
Ph.D.: University of Wisconsin
Role of Calcium and the Cytoskeleton in Cell Division and Development
Studies on cell division and plant cell growth constitute the focus of our research. In cell division, we examine the process of cytokinesis, giving particular attention to the cytoskeleton (microtubules and microfilaments), and to calcium ions, which together participate in the elaboration and positioning of the new cross wall. In studies of cell expansion, we examine tip growth of pollen tubes, a rapidly growing and highly polarized cell essential for sexual reproduction in flowering plants. Attention is directed to the actin cytoskeleton, and to calcium ions, which contribute to the flow, aggregation and fusion of vesicles necessary for growth.
Throughout these studies, emphasis is given to the dynamic processes, including growth and intracellular motility, as observed in living cells. To visualize the cytoskeleton we inject fluorescent analogs, (fluorescent tubulin for microtubules) or vital dyes (rhodamine phalloidin for microfilaments) permitting us to observe the structure and transformation of these elements using confocal fluorescence microscopy. For intracellular calcium we use vital fluorescent indicator dyes. In pollen tubes we observe steep tip-focused gradients of calcium at the growing apex. Recent studies show that the magnitude of this gradient oscillates in phase with growth. Finally, in studies of calcium, we also use the ion specific vibrating electrode to examine localized extracellular currents and determine their association with growth. Taken together, these studies are permitting us to obtain a more complete understanding of vital physiological processes as they relate to cell division, growth and development.
Hepler, P.K. and Gunning, B.E.S. Confocal microscopy of plant cells. Protoplasma (in press).
Franklin-Tong, V.E., Hackett, G. and Hepler, P.K. Ratio-imaging of Ca2+ in the self-incompatibility response in pollen tubes of Papaver rhoeas. Plant J. (in press).
Huang, F.Y., Philosoph-Hadas, S., Meir, S., Callaham, D.A., Zelcer, A. and Hepler, P.K. Role of cytosolic calcium signaling and regulation of leaf senescence: direct estimation of cytosolic Ca2+ levels in parsley mesophyll cells during leaf senescence. Plant Physiol. (in press).
Vos, J.W. and Hepler, P.K. (1998) Calmodulin is uniformly distributed during cell division in living stamen hair cells of Tradescantia virginiana. Protoplasma 201, 158-171.
Hepler, P.K. and Gunning, B.E.S. (1998) Confocal fluorescence microscopy of plant cells. Protoplasma 201, 121-157.
Holdaway-Clark, T.L., Feijo, J.A., Hackett, G.R., Kunkel, J. and Hepler, P.K. (1997) Pollen tube growth and the intracellular calcium gradient oscillate in phase while extracellular calcium influx is delayed. Plant Cell 9, 1999-2010.
Valster, A.H. and Hepler, P.K. (1997) Caffeine inhibition of cytokinesis: effect on the phragmoplast cytoskeleton in living Tradescantia stamen hair cells. Protoplasma 196, 155-166.
Vidali, L. and Hepler, P.K. (1997) Characterization and localization of profilin in pollen tubes of Lilium longiflorum. Cell Motil. Cytoskel. 36, 323-338.