The role of calcium, membranes and the cytoskeleton in cell division and development
Current interest centers around the role of calcium, membranes and the cytoskeleton in cell division and development. Particular attention is being given to the occurrence of fluxes and/or gradients in the calcium ion concentration. Using high resolution ion imaging, we are attempting to elucidate the timing, location, and magnitude of calcium ion gradients, and to decipher their role in controlling plant cell division and growth. During mitosis, for example, we are specifically examining the role of calcium in regulating the formation of the cell plate during cytokinesis. For cell growth we are focusing on the presence and oscillation of apical ion gradients in tip growing pollen tubes and root hairs.
We are also elucidating the structure and dynamics of the cytoskeleton in living plant cells. Using microinjection to introduce appropriate analogs such as tubulin, actin, actin binding proteins and cell cycle factors, which are fluorescently tagged, we are able to visualize the structures into which these analogs become incorporated. Microtubules, for example, are observed in all major arrays of plant cells and their response to drugs, temperature and to calcium are being directly monitored. It is our goal to combine fluorescent analog cytochemistry, and calcium ion imaging to decipher how calcium ions regulate the cytoskeleton during 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).
Felle, H.H. and Hepler, P.K. 1997. The cytosolic [Ca2+]-gradient of Sinapsis alba root hairs as revealed by Ca2+-selective microelectrode tests and fura-dextran ratio imaging. Plant Physiol.114: 39-45.
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.
Lancelle, S.A., Cresti, M. and Hepler, P.K. 1997. Growth inhibition and recovery in freeze-substituted Lilium longiflorum pollen tubes: structural effects of caffeine. Protoplasma 196: 21-33.
Miller, D.D., Lancelle, S.A. and Hepler, P.K. 1996. Actin MFs do not form a dense meshwork in Lilium longiflorum pollen tube tips. Protoplasma195: 123-132.
Hepler, P.K. and Hush, J.M. 1996. Behavior of microtubules in living plant cells. Plant Physiol. 112: 455-461.
Li, Y.Q., Zhang, H.Q., Pierson, E.S., Huang, F.Y., Linskens, H.F., Hepler, P.K. and Cresti, M. 1996. Enforced growth-rate fluctuation causes pectin ring formation in the cell wall of Lilium longiflorum pollen tubes. Planta200: 41-49.
Baskin, T.I., Miller, D.D., Vos, J.W., Wilson, J.E. and Hepler, P.K. 1996. Cryofixing single cells and multicellular specimens enhances structure and immunocytochemistry for light microscopy. J. Microsc. 182: 149-161.
Hush, J.M., Wu, L.P., John, P.C.L., Hepler, L.H. and Hepler, P.K. 1996. Plant MPF disassembles the microtubule preprophase band and accelerates prophase progression in Tradescantia. Cell Biol. Inter. 20: 275-287.
Staehelin, L.A. and Hepler, P.K. 1996. Cytokinesis in higher plants. Cell84: 821-824.
Wasteneys, G.O., Collings, D.A., Gunning, B.E.S., Hepler, P.K. and Menzel, D. 1996. Actin in living and fixed characean internodal cells: identification of a cortical array of fine actin strands and chloroplast actin rings. Protoplasma 190: 25-38.
Pierson, E.S., Miller, D.D., Callaham, D.A., van Aken, J., Hackett, G. and Hepler, P.K. 1996. Tip-localized calcium entry fluctuates during pollen tube growth. Dev. Biol. 174: 160-173.
Kim, M., Hepler, P.K., Eun, S.O., Ha, S.A. and Lee, Y. 1995. Actin filaments in mature guard cells are radially distributed and involved in stomatal movement. Plant Physiol. 109: 1077-1084.
Holzinger, A., Callaham, D.A., Hepler, P.K. and Meindl, U. 1995. Free calcium in Micrasterias: local gradients are not detected in growing lobes. Eur. J. Cell Biol. 67: 363-371.
Miller, D.D., Scordilis, S.P. and Hepler, P.K. 1995. Identification and localization of three classes of myosins in pollen tubes of Lilium longiflorum and Nicotiana alata. J. Cell Sci. 108: 2549-2563.
Pierson, E.S., Miller, D.D., Callaham, D.A., Shipley, A.M., Rivers, B.A., Cresti, M. and Hepler, P.K. 1994. Pollen tube growth is coupled to the extracellular calcium ion flux and the intracellular calcium gradient: effect of BAPTA buffers and hypertonic media. Plant Cell 6: 1815-1828.
Jürgens, M., Hepler, L.H., Rivers, B.A. and Hepler, P.K. 1994. BAPTA-calcium buffers modulate cell plate formation in stamen hairs of Tradescantia: evidence for calcium gradients. Protoplasma183: 86-99.
Meindl, U., Zhang, D.H. and Hepler, P.K. 1994. Spatial organization and dynamics of the cytoskeleton in living cells of Micrasterias. J. Cell Sci. 107: 1929-1934.
Hush, J.M., Wadsworth, P., Callaham, D.A. and Hepler, P.K. 1994. Quantification of microtubule dynamics in living plant cells using fluorescence redistribution after photobleaching. J. Cell Sci. 107: 775-784.
Hepler, P.K., Sek, F.J. and John, P.C.L. 1994. Nuclear concentration and mitotic dispersion of the essential cell cycle protein, p13, examined in living cells. Proc. Nat'l. Acad. Sci. U.S.A. 91: 2176-2180.