Peter K. Hepler

Peter K. Hepler
Born October 29, 1936
Dover, New Hampshire
Citizenship United States
Nationality American
Fields Cell biology, plant physiology, microscopy
Institutions Stanford University
University of Massachusetts at Amherst
Alma mater University of New Hampshire, B.S. Chemistry 1958
University of Wisconsin, Ph.D. Plant Cell Biology 1964
Known for Cell biology, plant physiology, microscopy

Website
Peter K. Hepler

Molecular & Cellular Biology

Peter Klock Hepler Hon FRMS is the Constantine J. Gilgut and Ray Ethan Torrey Professor Emeritus in the Biology Department of the University of Massachusetts at Amherst who is notable for his work on elucidating the roles of calcium,[1] membranes[2] and the cytoskeleton[3][4] in plant cell development and cell motility.

Personal life

Peter Klock Hepler was born on October 29, 1936, in Dover, New Hampshire, to Jesse Raymond Hepler[5][6][7] and Rebecca Orpha Peterson Hepler. He married Margaret (Peggy) Dennison Hunt on March 7, 1964. They have three children: Sarah, Lukas and Anna.[8] In an interview published in the Newsletter of the American Society of Plant Biologists, Hepler was asked, "What is your most treasured possession?" He answered, "My family; but I don't possess them."[9] Peter and Peggy Hepler live on a farm in Pelham, Massachusetts that was established by John Gray in 1740[10] and is now a part of the Kestrel Land Trust.[11]

University life

Peter Hepler graduated from Dover High School in 1954. He received his B.S. in chemistry from the University of New Hampshire in 1958 and earned his Ph.D. in plant cell biology from University of Wisconsin in 1964, studying the role of cortical microtubules in plant cell development with Eldon H. Newcomb. After receiving his Ph.D., Hepler served at the Walter Reed Army Institute of Research until 1966, studying malarial parasites. Hepler then returned to the University of Wisconsin for a postdoctoral fellowship[12] and then became a postdoctoral fellow with Keith Porter[13] at Harvard University from 1966-1967, where he continued his investigation of microtubules, focusing on their role in the mitotic apparatus and the phragmoplast of the endosperm cells of Haemanthus Katharinae. After being an assistant professor at Stanford University, Hepler joined the faculty in the Botany Department at the University of Massachusetts at Amherst. He was an associate professor from 1977 to 1980, a professor from 1980-1989, and became the Ray Ethan Torrey Professor in 1989 and the Constantine J. Gilgut Professor in 1998. Hepler retired from the Biology Department as the Constantine J. Gilgut and Ray Ethan Torrey Professor Emeritus, although he continues to do research.[14] Hepler spent many summers teaching and doing research at the Marine Biological Laboratory[15][16] at Woods Hole, Massachusetts. Hepler also participated in a multiyear international collaboration with Brian E. S. Gunning.[17]

Hepler was an Associate Editor of Protoplasma from 1994-2001 and Associate Editor of Plant Physiology from 1998-2000. He has been on the editorial boards of the Annual Review Plant Physiology, Plant and Cell Physiology, the Journal of Submicroscopic Cytology, Cell Motility and the Cytoskeleton, and BioEssays.

Research

Hepler's scientific method is to know thoroughly the classical botanical literature and then develop or apply modern physico-chemical techniques to answer salient and extensive biological questions using plants that are well-suited to answer those questions. In so doing, Hepler opened whole areas of research.[18][19] Hepler did pioneering work in showing the relationship of the microscopic elements of the cytoskeleton to the macroscopic properties of plant growth, development and function. He also did pioneering work on plasmodesmata,[20][21][22] stomatal function,[23][24][25][26] and in the development of techniques useful for answering questions using light[27][28][29][30][31] and electron microscopy.[32] Hepler's scientific publications with Barry A. Palevitz are notable for quoting Woody Allen and Yogi Berra.[33]

Hepler described his realization of the influence a review he and Palevitz[4] wrote on microtubules and microfilaments "to introduce new thoughts and promising avenues for future research" had with his characteristic self-deprecating sense of humor: "I became aware that the review was being read widely one summer (1979) while working in the library at the Marine Biological Laboratory. I turned to the library's volume of the Annual Review of Plant Physiology that contained our paper and when I put the volume down, it literally fell open at our article; worn edges on the pages and the penciled corrections of all the misspellings and punctuation errors indicated that the chapter had been thoroughly perused."[4]

Hepler, along with Ledbetter and Porter,[34] is considered to be a co-discoverer of microtubules.[13]

Microtubules and cell shape

In late 1962 and early 1963, Hepler tested the newly-developed procedure using a glutaraldehyde pre-fix followed by an osmium post-fix to study plant cell structure using an electron microscope.[35] Building on the earlier work by Sinnott and Bloch,[36] who had shown that wounding the existing tracheary elements in a Coleus stem induced neighboring parenchyma cells to differentiate into new tracheary elements, Hepler showed that cytoplasmic microtubules were localized specifically in the cortical cytoplasm immediately over the bands of new secondary wall thickenings.[37] Moreover, Hepler discovered that the microtubules were oriented parallel to the cellulose microfibrils of the newly-formed secondary wall thickenings. This work, along with the studies of Ledbetter and Porter[34] and Green[38] established the importance of cortical microtubules in controlling the alignment of cellulose microfibrils in the cell wall.[39][40] Further work with Barry Palevitz showed that microtubules were involved in orienting the cellulose microfibrils in the walls of guard cells in a pattern of radial micellation that is necessary for stomatal function.[41] Hepler, along with the husband and wife team of Dale Callaham and Sue Lancelle, developed a method to achieve rapid freeze fixation of particularly small plant cells that showed that cortical microtubules are closely associated with one another, actin microfilaments, the endoplasmic reticulum and the plasma membrane.[32][42]

Microtubules and cell motility

Building on the work of Shinya Inoué and Andrew Bajer using polarized light microscopy,[43] Hepler used electron microscopy to elucidate the nature of the microtubule/chromosome attachments at the kinetochore as well as the arrangement of the microtubules in the phragmoplast during the development of the new cell wall, where microtubules from both sides of the phragmoplast were seen to overlap with one another in the plane of the cell plate.[44]

Hepler realized that microtubules were dynamic structures that were deployed in various locations throughout the cell, and became interested in the mechanisms involved in microtubule organization in cells that lacked a microtubule-organizing center known as the centrosome. In order to understand how microtubule-organizing centers were generated, Hepler examined the de novo formation of the blepharoplast in the spermatogenous cells of Marsilea vestita. The blepharoplast in each spermatid generates 100–150 basal bodies, each of which gives rise to the 9+2 arrangement of microtubules in a cilium. During telophase of the penultimate division, flocculent material appears near clefts on the distal surfaces of the daughter nuclei. During prophase of the final division which gives rise to the spermatids, the flocculent material near each nucleus condenses to give rise to two blepharoplasts, which then separate, one going to each spermatid.[45]

While Hepler was successful in identifying an aggregation of material that possessed microtubule-organizing capacity, he was not able to specify the biophysical mechanisms involved in organization. After Richard Weisenberg[46] discovered that microtubule polymerization was sensitive to calcium concentration, Hepler realized that he had already seen a close association between elements of the endoplasmic reticulum and microtubules in the mitotic apparatus and in the phragmoplast and suggested that these membranes may function in controlling the concentration of free calcium in the mitotic apparatus.[47] Along with Susan Wick and Steve Wolniak, Hepler showed that the endoplasmic reticulum contained stores of calcium and suggested that the endoplasmic reticulum may locally control the calcium concentration and thus the polymerization/depolymerization of microtubules. Subsequently,[48][49] Hepler, along with Dale Callaham, Dahong Zhang, and Patricia Wadsworth, observed calcium ion transients during mitosis[50][51] and showed that the microinjection of calcium ions into the mitotic spindle does regulate the depolymerization of microtubules and the movement of chromosomes to the poles during mitosis.[52][53][54]

Microfilaments and cytoplasmic streaming

Hepler identified actin microfilaments in bundles at the ectoplasm-endoplasm interface of Nitella internodal cells by showing that the bundles bound heavy meromyosin, giving the characteristic arrowhead arrangement.[55][56] The actin microfilaments had the correct polarity to be part of the actomyosin motor that provides the motive force for cytoplasmic streaming in these giant algal cells.[57]

Calcium and plant development

Hepler has shown that calcium ions are a central regulator of plant growth and development[58] specifically demonstrating that calcium is important for tip growth[59][60][61] and in phytochrome.[62][63] and cytokinin[64][65][66] action.

Honors and awards

References

  1. Hepler, P. K. and R. O. Wayne (1993). "This Week's Citation Classic" (PDF). Current Contents (July 26, 1993) (30): 8. Retrieved October 6, 2016.
  2. Hepler, P. K., S. M. Wick and S. M. Wolniak (1981). The structure and role of membranes in the mitotic apparatus. in: International Cell Biology 1980–1981, H.G. Schweiger, ed. Berlin: Springer-Verlag. pp. 673–686.
  3. Hepler, P. K. and B. A. Palevitz (1974). "Microtubules and microfilaments". Annual Review of Plant Physiology. 25: 309–362.
  4. 1 2 3 Hepler, P. K. and B. A. Palevitz (1986). "Microtubules and microfilaments" (PDF). Current Contents (August 11, 1986) (32): 20. Retrieved October 7, 2016.
  5. Hepler, J. R. (1922). Methods in Forcing Rhubarb: M.S. Thesis. University of Wisconsin. Retrieved October 7, 2016.
  6. Hepler, Billy (2012). "America's Youngest Seed Grower" (PDF). Heritage Farm Companion (Summer): 6–9.
  7. "A Bean Collector's Window". Retrieved October 18, 2016.
  8. Hepler, Anna. "Anna Hepler Intricate Universe". Retrieved October 7, 2016.
  9. "Membership Corner" (PDF) (31(5), 22). APBS News September/October 2004.
  10. "Hepler Family (Pelham, MA)". UmassAmherst: MassWoods. Retrieved October 6, 2016.
  11. "Kestrel Land Trust: Conserve the Valley You Love". Kestrel Land Trust. Retrieved October 6, 2016.
  12. VandenBosch, K. A., W. Becker and B. A Palevitz (1996). "The natural history of a scholar and gentleman: A biography of Eldon H. Newcomb". Protoplasma. 195: 4–11. Retrieved October 7, 2016.
  13. 1 2 Hepler, P. K., J. D. Pickett-Heaps and B. E. S. Gunning (2013). "Some retrospectives on early studies of plant microtubules". The Plant Journal. 75 (2): 189–201. Retrieved October 7, 2016.
  14. Hepler, Peter K. (2016). "Founders' Review: The Cytoskeleton and Its Regulation by Calcium and Protons" (PDF). Plant Physiology. 170: 3–22. Retrieved October 6, 2016.
  15. "MBL Society Members". Marine Biological Laboratory. Retrieved October 6, 2016.
  16. "Physiology 1981". History of the Marine Biological Laboratory. Retrieved October 6, 2016.
  17. Hepler, P. K., and B. E. S. Gunning (1998). "Confocal fluorescence microscopy of plant cells". Protoplasma. 201 (3): 121–157. Retrieved October 6, 2016.
  18. 1 2 "AAAS Members Elected as Fellows". AAAS. Retrieved October 6, 2016.
  19. 1 2 "Members in the News". ASPB Newsletter 33(3), 26. April 2010. Retrieved October 6, 2016.
  20. Hepler, P. K., and E. H. Newcomb (1967). "Fine structure of cell plate formation in the apical meristem of Phaseolus roots". Journal of Ultrastructural Research. 19 (5-6): 498–513. Retrieved October 7, 2016.
  21. Palevitz, B. A., and P. K. Hepler (185). "Changes in dye coupling of stomatal cells of Allium and Commelina demonstrated by microinjection of Lucifer yellow". Planta. 164 (4): 473–479. Retrieved October 6, 2014.
  22. Turgeon, R., and P. K. Hepler (1989). "Symplastic continuity between mesophyll and companion cells in minor veins of mature Cucurbita pepo L. leaves". Planta. 179 (1): 24–31. Retrieved October 6, 2016.
  23. Zeiger, E., and P. K. Hepler (1976). "Production of Guard Cell Protoplasts from Onion and Tobacco". Plant Physiology. 58: 492–498. Retrieved October 6, 2016.
  24. Zeiger, E., W. Moody, P. Hepler and F. Varela (1977). "Light-sensitive membrane potentials in onion guard cells". Nature. 270: 270–271. doi:10.1038/270270a0. Retrieved October 6, 2016.
  25. Zeiger, E., and P. K. Hepler (1977). "Light and stomatal function: blue light stimulates swelling of guard cell protoplasts". Science. 196 (4292): 887–889. Retrieved October 6, 2016.
  26. Zeiger, E., and P. K. Hepler (1979). "Blue light-induced, intrinsic vacuolar fluorescence in onion guard cells". Journal of Cell Science. 37: 1–10. Retrieved October 6, 2016.
  27. Zhang, D., P. Wadsworth, and P. K. Hepler (1990). "Microtubule dynamics in living dividing cells: Confocal imaging of microinjected fluorescent brain tubulin". Proc. Natl. Acad. Sci. USA. 87: 8820–8824. PMC 55051Freely accessible.
  28. Zhang, D., P. Wadsworth and P. K. Hepler (1993). "Dynamics of microfilaments are similar, but distinct from microtubules during cytokinesis in living, dividing plant cells". Cell Motility and the Cytoskeleton. 24: 151–155. Retrieved October 7, 2016.
  29. Valster, A. H., E. S. Pierson, Valenta, P. K. Hepler and A. M. C. Emons (1997). "Probing the Plant Actin Cytoskeleton during Cytokinesis and Interphase by Profilin Microinjection". The Plant Cell. 9: 1815–1824. Retrieved October 7, 2016.
  30. Vos, J. W., A. H. Valster and P. K. Hepler (1988). "Methods for Studying Cell Division in Higher Plants". Methods in Cell Biology. 61: 413–437. Retrieved October 7, 2016.
  31. Hepler, P. K., and J. Hush (1996). "Behavior of Microtubules in Living Plant Cells". Plant Physiology. 112: 455–461. PMC 157968Freely accessible.
  32. 1 2 Lancelle, S. A., D. A. Callaham and P. K. Hepler (1986). "A method for rapid freeze fixation of plant cells". Protoplasma. 131: 153–165. Retrieved October 6, 2016.
  33. "Poems and Quotations About the MicroWorld". Microscopy Society of America. Retrieved October 6, 2016.
  34. 1 2 Ledbetter, M. C., and K. R. Porter (1963). "A 'microtubule' in plant cell fine structure". Journal of Cell Biology. 19: 239–250.
  35. Newcomb, E. H. (1996). "A career in science: Fulfillment of a dream". Protoplasma. 195 (1-4): 1–3. Retrieved October 7, 2016.
  36. Sinnott, E. W., and R. Bloch (1945). "The cytoplasmic basis of intercellular patterns in vascular differentiation". American Journal of Botany. 32: 151–156.
  37. Hepler, P. K., and E. H. Newcomb (1964). "The Fine Structure of Young Tracheary Xylem Elements Arising by Redifferentiation of Parenchyma in Wounded Coleus Stem". Journal of Experimental Botany. 14 (3): 496–503. Retrieved October 6, 2016.
  38. Green, P. B. (1962). "Mechanism for plant cellular morphogenesis". Science. 138: 1404–1405.
  39. Torrey, J. G., D. E. Fosket and P. K. Hepler (1971). "Xylem Formation: A Paradigm of Cytodifferentiation in Higher Plants: Plant cells divide and differentiate under the control of changing hormone levels. Xylem offers a model tissue for the study of these cellular events". American Scientist. 59 (3): 338–352. JSTOR 27829621.
  40. Wasteneys, G. O. and F. Brandizzi (2013). "A Glorious Half-Century of Microtubules". The Plant Journal. 75 (2): 185–188. Retrieved October 6, 2016.
  41. Palevitz, B. A., and P. K. Hepler (1976). "Cellulose microfibril orientation and cell shaping in developing guard cells of Allium: The role of microtubules and ion accumulation". Planta. 132: 71–93. doi:10.1007/BF00390333. PMID 24424910.
  42. Lancelle, S. A., M. Cresti and P. K. Hepler (1987). "Ultrastructure of the cytoskeleton in freeze-substituted pollen tubes of Nicotiana alata". Protoplasma. 140: 141–150. Retrieved October 6, 2016.
  43. Inoué, S. and A. Bajer (1961). "Birefringence in endosperm mitosis". Chromosoma. 12: 48–63.
  44. Hepler, P. K., and W. T. Jackson (1968). "Microtubules and early stages of cell plate formation in the endosperm of Haemanthus katherinae Baker". Journal of Cell Biology. 38: 437–446.
  45. Hepler, P. K. (1976). "The blepharoplast of Marsilea: Its de novo formation and spindle association". Journal of Cell Science. 21: 361–390. Retrieved October 6, 2016.
  46. Weisenberg, R. C. (1972). "Microtubule formation in vitro in solutions containing low calcium concentration". Science. 177: 1104–1105. Retrieved October 6, 2016.
  47. Hepler, P. K. (1980). "Membranes in the mitotic apparatus of barley cells". Journal of Cell Biology. 86: 490–499. Retrieved October 6, 2016.
  48. Wick, S. M., and P. K. Hepler (1980). "Localization of Ca++-containing antimonate precipitates during mitosis". Journal of Cell Biology: 500–513. Retrieved October 6, 2016.
  49. Wolniak, S. M., P. K. Hepler, and W. T. Jackson (1980). "Detection of the membrane-calcium distribution during mitosis in Haemanthus endosperm with chlorotetracycline". Journal of Cell Biology. 87: 23–32. Retrieved October 6, 2016.
  50. Hepler, P. K., and D. A. Callaham (1987). "Free calcium increases during anaphase in stamen hair cells of Tradescantia". Journal of Cell Biology. 105: 2137–2143. Retrieved October 7, 2016.
  51. Hepler, P. K. (1989). "Calcium transients during mitosis: Observations in flux". Journal of Cell Biology. 109: 2567–2573. Retrieved October 7, 2016.
  52. Zhang, D. H. (1990). "Regulation of anaphase chromosome motion in Tradescantia stamen hair cells by calcium and related signaling agents". Journal of Cell Biology. 111: 171–182. Retrieved October 6, 2016.
  53. Zhang, D. H., P. Wadsworth, and P. K. Hepler (1990). "Microtubule dynamics in living dividing plant cells: Confocal imaging of microinjected fluorescent brain tubulin". Proc. Natl. Acad. Sci. USA. 87 (22): 8820–8824. Retrieved October 6, 2016.
  54. Zhang, D. H., P. Wadsworth and P. K. Hepler (1992). "Modulation of anaphase spindle microtubule structure in stamen hair cells of Tradescantia by calcium and related agents". Journal of Cell Science. 102 (1): 79–89. Retrieved October 6, 2016.
  55. Palevitz, B. A., J. F. Ash, and P. K. Hepler (1974). "Actin in the green alga, Nitella". Proc. Natl. Acad. Sci. USA. 71 (2): 263–266. PMC 388005Freely accessible.
  56. Palevitz, B. A., and P. K. Hepler (1975). "Identification of actin in situ at the ectoplasm-endoplasm interface of Nitella. Microfilament-chloroplast association". Journal of Cell Biology. 65 (1): 29–38. Retrieved October 6, 2016.
  57. Kersey, Y. M., P. K. Hepler, B. A. Palevitz, and N. K. Wessells (1976). "Polarity of actin filaments in Characean algae". Proc. Natl. Acad. Sci. USA. 73 (1): 165–167. PMC 335861Freely accessible.
  58. Hepler, P. K. (2005). "Historical Perspective Essay: Calcium: a central regulator of plant growth and development". Plant Cell. 17 (8): 42–55. Retrieved October 6, 2016.
  59. Miller, D. D., D. A. Callaham, D. J. Gross and P. K. Hepler (1992). "Free Ca2+ gradient in growing pollen tubes of Lilium". Journal of Cell Science. 101: 7–12. Retrieved October 7, 2016.
  60. Wilsen, K. L. and P. K. Hepler (2007). "Sperm Delivery in Flowering Plants: The Control of Pollen Tube Growth". BioScience. 57 (10): 835–844. Retrieved October 20, 2016.
  61. P. K. Hepler, J. G. Kunkel, C. M. Rounds, L. J. Winship (2012). "Calcium entry into pollen tubes". Trends in Plant Science. 17 (1): 32–38. Retrieved October 7, 2016.
  62. Wayne, R., and P. K. Hepler (1984). "The Role of Calcium Ions in Phytochrome-mediated germination of spores of Onoclea sensibilis L.". Planta. 160: 12–20. Retrieved October 7, 2016.
  63. Wayne, R., and P. K. Hepler (1985). "Red Light Stimulates and Increase in Intracellular Calcium in the Spores of Onoclea sensibilis" (PDF). Plant Physiology. 77: 8–11. Retrieved October 7, 2016.
  64. Saunders, M. J., and P. K. Hepler (1982). "Calcium ionophore A23187 stimulates cytokinin-like mitosis in Funaria". Science. 217: 943–945.
  65. Saunders, M. J., and P. K. Hepler (1981). "Localization of membrane-associated calcium following cytokinin treatment in Funaria using chlortetracycline". Planta. 152: 272–281. Retrieved October 6, 2016.
  66. Conrad, P. A., and P. K. Hepler (1988). "The effect of 1,4-dihydropyridines on the initiation and development of gametophore buds in the moss Funaria". Plant Physiology. 86: 684–687. Retrieved October 6, 2016.
  67. "Jeanette Siron Pelton Award". Botanical Society of America. Retrieved October 8, 2016.
  68. "Hepler named fellow of American Society of Plant Biologists". UmassAmherst News & Media Relations. Retrieved October 6, 2016.
  69. "Peter K. Hepler". AAAS. Retrieved October 8, 2016.
  70. "Hepler wins national award for plant discoveries". UmassAmherst News & Media Relations. Retrieved October 6, 2016.
  71. "RMS Honorary Fellows". Royal Microscopical Society. Retrieved October 6, 2016.
  72. "Hepler Named Honorary Fellow of Royal Microscopical Society". UmassAmherst News & Media Relations. Retrieved October 6, 2016.
  73. "Peter K. Hepler Research Scholarship". UmassAmherst. Retrieved October 6, 2016.
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