Peter K. Hepler

Last updated
Peter K. Hepler
Peter Hepler.jpg
Born (1936-10-29) October 29, 1936 (age 86)
Dover, New Hampshire
Nationality American
CitizenshipUnited States
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
Scientific career
Fields Cell biology, plant physiology, microscopy
Institutions Stanford University
University of Massachusetts at Amherst
Website Peter K. Hepler
Molecular & Cellular Biology

Peter Klock Hepler HonFRMS (born 1936) 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.

Contents

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, Anna [8] and Lukas. Peter and Peggy have six grandchildren: Finn, Leif, Louisa (Lulu), Jesse, Marit, and Haakon. 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 [10] in 1740 [11] and is now a part of the Kestrel Land Trust. [12]

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 [13] and then became a postdoctoral fellow with Keith Porter [14] at Harvard University from 1966 to 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 to 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. [15] Hepler spent many summers teaching and doing research at the Marine Biological Laboratory [16] [17] at Woods Hole, Massachusetts. Hepler also participated in a multiyear international collaboration with Brian E. S. Gunning. [18]

Hepler was an Associate Editor of Protoplasma from 1994 to 2001 and Associate Editor of Plant Physiology from 1998 to 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 .[ citation needed ]

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. [19] [20] 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, [21] [22] [23] stomatal function, [24] [25] [26] [27] the role of calcium in plant development [28] and in the development of techniques useful for answering questions using light [29] [30] [31] [32] [33] and electron microscopy. [34] Hepler's scientific publications with Barry A. Palevitz are notable for quoting Woody Allen and Yogi Berra. [35]

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, [36] is considered to be a co-discoverer of microtubules. [14]

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. [37] Building on the earlier work by Sinnott and Bloch, [38] 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. [39] 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 [36] and Green [40] established the importance of cortical microtubules in controlling the alignment of cellulose microfibrils in the cell wall. [41] [42] 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. [43] 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. [34] [44]

Microtubules and cell motility

Building on the work of Shinya Inoué and Andrew Bajer using polarized light microscopy, [45] 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. [46]

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. [47]

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 [48] 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. [49] 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, [50] [51] Hepler, along with Dale Callaham, Dahong Zhang, and Patricia Wadsworth, observed calcium ion transients during mitosis [52] [53] 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. [54] [55] [56]

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. [57] [58] 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. [59]

Calcium and plant development

Hepler has shown that calcium ions are a central regulator of plant growth and development [60] specifically demonstrating that calcium is important for tip growth [61] [62] [63] and in phytochrome. [64] [65] and cytokinin [66] [67] [68] action.

Pollen tube growth

Hepler's research is currently aimed at finding the ionic and molecular components that make up the pacemaker that regulates the oscillatory growth of pollen tubes. He has shown that calcium ions and protons are essential for growth. [69] The intracellular free calcium ions exist in a gradient dropping from 3000 nM at the tip to 200 nM 20 μm from the tip [70] and the intracellular H+ gradient falls from pH 6.8 at the tip to pH 7.5 10–30 μm from the tip. [71] The higher concentrations of intracellular Ca2+ and H+ at the tip result from the localization of the influx of these ions at the tip. The protons are effluxed at a region on the sides of the tube that corresponds to the location of the intracellular alkaline band. [72] Energy is required for pollen tube growth [73] and an H+-ATPase may mediate the efflux. Hepler has shown that the magnitude of the intracellular calcium and proton gradients and the extracellular fluxes of these ions oscillate with a period of 15-50 s. This period is identical to the period of oscillation in the rate of pollen tube growth, however, the intracellular calcium peak follows the growth rate peak by 1–4 seconds, and the extracellular calcium peak follows the growth rate peak by 11–15 seconds. [74] The delay between the extracellular and intracellular calcium peaks indicates that calcium ions do not immediately enter the cytoplasmic pool. Hepler postulates that the extracellular influx of calcium is not governed by the plasma membrane but by changes in the ion-binding properties of the pectin within the cell wall. The pectin is secreted in its uncharged methylester form. Subsequently, a pectin methylesterase in the wall results in the de-esterification of the methyl groups that yields carboxyl residues that bind calcium and form calcium-pectate cross-bridges. This calcium binding may account for the bulk of the observed extracellular current. The intracellular calcium gradient may direct the location of secretion of cell wall components that define the direction of pollen tube growth.

The intracellular components that contribute to pollen tube growth include the actin-mediated transfer of Golgi-derived secretory vesicles filled with methylesterified homogalacturonans and pectin methylesterase synthesized on the ER to the growing tip. [75] The secretion of the vesicles at the growing tip anticipates the increase in growth rate, [76] indicating that the turgor pressure driven intussusception of the methylesterified pectin into the cell wall at the growing tip and its subsequent demethylesterification by pectin methylesterase may relax the cell wall by robbing the load-bearing calcium pectate bonds of its Ca2+. [77] This would result in a slightly delayed yet increased growth rate. The removal of the methoxy groups in the pectins at the flanks of the apical dome unmasks their negatively charged carboxylate groups. The anionic homogalacturonans then bind Ca2+ and become stiffer as the new apical dome, which will incorporate more methylesterified pectins and pectin methylesterase, grows away from the stiffened flanks composed of calcium pectate. The external Ca2+ concentration is critical. When the external Ca2+ concentration is below 10 μM, the amount of calcium pectate is so low that the cell wall is too weak and the pollen tube bursts. When the external Ca2+ concentration is above 10 mM, the amount of calcium pectate is so high that the cell wall is too stiff and the pollen tube will not grow.

Honors and awards

Related Research Articles

<span class="mw-page-title-main">Microtubule</span> Polymer of tubulin that forms part of the cytoskeleton

Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nm and have an inner diameter between 11 and 15 nm. They are formed by the polymerization of a dimer of two globular proteins, alpha and beta tubulin into protofilaments that can then associate laterally to form a hollow tube, the microtubule. The most common form of a microtubule consists of 13 protofilaments in the tubular arrangement.

<span class="mw-page-title-main">Fertilisation</span> Union of gametes of opposite sexes during the process of sexual reproduction to form a zygote

Fertilisation or fertilization, also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. While processes such as insemination or pollination which happen before the fusion of gametes are also sometimes informally referred to as fertilisation, these are technically separate processes. The cycle of fertilisation and development of new individuals is called sexual reproduction. During double fertilisation in angiosperms the haploid male gamete combines with two haploid polar nuclei to form a triploid primary endosperm nucleus by the process of vegetative fertilisation.

<span class="mw-page-title-main">Pseudopodia</span> False leg found on slime molds, archaea, protozoans, leukocytes and certain bacteria

A pseudopod or pseudopodium is a temporary arm-like projection of a eukaryotic cell membrane that is emerged in the direction of movement. Filled with cytoplasm, pseudopodia primarily consist of actin filaments and may also contain microtubules and intermediate filaments. Pseudopods are used for motility and ingestion. They are often found in amoebas.

<span class="mw-page-title-main">Cytoskeleton</span> Network of filamentous proteins that forms the internal framework of cells

The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is composed of similar proteins in the various organisms. It is composed of three main components, microfilaments, intermediate filaments and microtubules, and these are all capable of rapid growth or disassembly dependent on the cell's requirements.

<span class="mw-page-title-main">Cytokinesis</span> Part of the cell division process

Cytokinesis is the part of the cell division process during which the cytoplasm of a single eukaryotic cell divides into two daughter cells. Cytoplasmic division begins during or after the late stages of nuclear division in mitosis and meiosis. During cytokinesis the spindle apparatus partitions and transports duplicated chromatids into the cytoplasm of the separating daughter cells. It thereby ensures that chromosome number and complement are maintained from one generation to the next and that, except in special cases, the daughter cells will be functional copies of the parent cell. After the completion of the telophase and cytokinesis, each daughter cell enters the interphase of the cell cycle.

<span class="mw-page-title-main">Microfilament</span> Filament in the cytoplasm of eukaryotic cells

Microfilaments, also called actin filaments, are protein filaments in the cytoplasm of eukaryotic cells that form part of the cytoskeleton. They are primarily composed of polymers of actin, but are modified by and interact with numerous other proteins in the cell. Microfilaments are usually about 7 nm in diameter and made up of two strands of actin. Microfilament functions include cytokinesis, amoeboid movement, cell motility, changes in cell shape, endocytosis and exocytosis, cell contractility, and mechanical stability. Microfilaments are flexible and relatively strong, resisting buckling by multi-piconewton compressive forces and filament fracture by nanonewton tensile forces. In inducing cell motility, one end of the actin filament elongates while the other end contracts, presumably by myosin II molecular motors. Additionally, they function as part of actomyosin-driven contractile molecular motors, wherein the thin filaments serve as tensile platforms for myosin's ATP-dependent pulling action in muscle contraction and pseudopod advancement. Microfilaments have a tough, flexible framework which helps the cell in movement.

<span class="mw-page-title-main">Pollen tube</span> Tubular structure to conduct male gametes of plants to the female gametes

A pollen tube is a tubular structure produced by the male gametophyte of seed plants when it germinates. Pollen tube elongation is an integral stage in the plant life cycle. The pollen tube acts as a conduit to transport the male gamete cells from the pollen grain—either from the stigma to the ovules at the base of the pistil or directly through ovule tissue in some gymnosperms. In maize, this single cell can grow longer than 12 inches (30 cm) to traverse the length of the pistil.

<span class="mw-page-title-main">Cleavage furrow</span>

In cell biology, the cleavage furrow is the indentation of the cell's surface that begins the progression of cleavage, by which animal and some algal cells undergo cytokinesis, the final splitting of the membrane, in the process of cell division. The same proteins responsible for muscle contraction, actin and myosin, begin the process of forming the cleavage furrow, creating an actomyosin ring. Other cytoskeletal proteins and actin binding proteins are involved in the procedure.

<span class="mw-page-title-main">Actin</span> Family of proteins

Actin is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in muscle fibrils. It is found in essentially all eukaryotic cells, where it may be present at a concentration of over 100 μM; its mass is roughly 42 kDa, with a diameter of 4 to 7 nm.

<span class="mw-page-title-main">Cytoplasmic streaming</span> Flow of the cytoplasm inside the cell

Cytoplasmic streaming, also called protoplasmic streaming and cyclosis, is the flow of the cytoplasm inside the cell, driven by forces from the cytoskeleton. It is likely that its function is, at least in part, to speed up the transport of molecules and organelles around the cell. It is usually observed in large plant and animal cells, greater than approximately 0.1 mm. In smaller cells, the diffusion of molecules is more rapid, but diffusion slows as the size of the cell increases, so larger cells may need cytoplasmic streaming for efficient function.

Self-incompatibility (SI) is a general name for several genetic mechanisms that prevent self-fertilization in sexually reproducing organisms, and thus encourage outcrossing and allogamy. It is contrasted with separation of sexes among individuals (dioecy), and their various modes of spatial (herkogamy) and temporally (dichogamy) separation.

<span class="mw-page-title-main">Plasmodesma</span> A pore connecting between adjacent plant cells

Plasmodesmata are microscopic channels which traverse the cell walls of plant cells and some algal cells, enabling transport and communication between them. Plasmodesmata evolved independently in several lineages, and species that have these structures include members of the Charophyceae, Charales, Coleochaetales and Phaeophyceae, as well as all embryophytes, better known as land plants. Unlike animal cells, almost every plant cell is surrounded by a polysaccharide cell wall. Neighbouring plant cells are therefore separated by a pair of cell walls and the intervening middle lamella, forming an extracellular domain known as the apoplast. Although cell walls are permeable to small soluble proteins and other solutes, plasmodesmata enable direct, regulated, symplastic transport of substances between cells. There are two forms of plasmodesmata: primary plasmodesmata, which are formed during cell division, and secondary plasmodesmata, which can form between mature cells.

<span class="mw-page-title-main">Phragmoplast</span> Structure in dividing plant cells that builds the daughter cell wall

The phragmoplast is a plant cell specific structure that forms during late cytokinesis. It serves as a scaffold for cell plate assembly and subsequent formation of a new cell wall separating the two daughter cells. The phragmoplast can only be observed in Phragmoplastophyta, a clade that includes the Coleochaetophyceae, Zygnematophyceae, Mesotaeniaceae, and Embryophyta. Some algae use another type of microtubule array, a phycoplast, during cytokinesis.

Chemotropism is defined as the growth of organisms navigated by chemical stimulus from outside of the organism. It has been observed in bacteria, plants and fungi. A chemical gradient can influence the growth of the organism in a positive or negative way. Positive growth is characterized by growing towards a stimulus and negative growth is growing away from the stimulus.

<span class="mw-page-title-main">Motor protein</span> Class of molecular proteins

Motor proteins are a class of molecular motors that can move along the cytoplasm of cells. They convert chemical energy into mechanical work by the hydrolysis of ATP. Flagellar rotation, however, is powered by a proton pump.

<span class="mw-page-title-main">Cell cortex</span> Layer on the inner face of a cell membrane

The cell cortex, also known as the actin cortex, cortical cytoskeleton or actomyosin cortex, is a specialized layer of cytoplasmic proteins on the inner face of the cell membrane. It functions as a modulator of membrane behavior and cell surface properties. In most eukaryotic cells lacking a cell wall, the cortex is an actin-rich network consisting of F-actin filaments, myosin motors, and actin-binding proteins. The actomyosin cortex is attached to the cell membrane via membrane-anchoring proteins called ERM proteins that plays a central role in cell shape control. The protein constituents of the cortex undergo rapid turnover, making the cortex both mechanically rigid and highly plastic, two properties essential to its function. In most cases, the cortex is in the range of 100 to 1000 nanometers thick.

The latrunculins are a family of natural products and toxins produced by certain sponges, including genus Latrunculia and Negombata, whence the name is derived. It binds actin monomers near the nucleotide binding cleft with 1:1 stoichiometry and prevents them from polymerizing. Administered in vivo, this effect results in disruption of the actin filaments of the cytoskeleton, and allows visualization of the corresponding changes made to the cellular processes. This property is similar to that of cytochalasin, but has a narrow effective concentration range. Latrunculin has been used to great effect in the discovery of cadherin distribution regulation and has potential medical applications. Latrunculin A, a type of the toxin, was found to be able to make reversible morphological changes to mammalian cells by disrupting the actin network.

<span class="mw-page-title-main">Preprophase</span> Cell cycle phase only found in plants

Preprophase is an additional phase during mitosis in plant cells that does not occur in other eukaryotes such as animals or fungi. It precedes prophase and is characterized by two distinct events:

  1. The formation of the preprophase band, a dense microtubule ring underneath the plasma membrane.
  2. The initiation of microtubule nucleation at the nuclear envelope.
<span class="mw-page-title-main">Randy Wayne (biologist)</span>

Randy O. Wayne is an associate professor of plant biology at Cornell University. Along with his former colleague Peter K. Hepler, Wayne established the role of calcium in regulating plant growth. Their 1985 article Calcium and Plant Development was awarded the "Citation Classic" award from Current Contents magazine. They researched how plant cells sense gravity through pressure, the water permeability of plant membranes, light microscopy, as well as the effects of calcium on plant development. Wayne authored two textbooks, including Plant Cell Biology: From Astronomy to Zoology and Light and Video Microscopy.

<span class="mw-page-title-main">Intracellular transport</span> Directed movement of vesicles and substances within a cell

Intracellular transport is the movement of vesicles and substances within a cell. Intracellular transport is required for maintaining homeostasis within the cell by responding to physiological signals. Proteins synthesized in the cytosol are distributed to their respective organelles, according to their specific amino acid’s sorting sequence. Eukaryotic cells transport packets of components to particular intracellular locations by attaching them to molecular motors that haul them along microtubules and actin filaments. Since intracellular transport heavily relies on microtubules for movement, the components of the cytoskeleton play a vital role in trafficking vesicles between organelles and the plasma membrane by providing mechanical support. Through this pathway, it is possible to facilitate the movement of essential molecules such as membrane‐bounded vesicles and organelles, mRNA, and chromosomes.

References

  1. ↑ Hepler, P. K.; R. O. Wayne (July 26, 1993). "This Week's Citation Classic" (PDF). Current Contents (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.{{cite book}}: CS1 maint: multiple names: authors list (link)
  3. ↑ Hepler, P. K.; B. A. Palevitz (1974). "Microtubules and microfilaments". Annual Review of Plant Physiology. 25: 309–362. doi:10.1146/annurev.pp.25.060174.001521.
  4. 1 2 3 Hepler, P. K.; B. A. Palevitz (August 11, 1986). "Microtubules and microfilaments" (PDF). Current Contents (32): 20. Retrieved October 7, 2016.
  5. ↑ Hepler, J. R. (1922). Methods in Forcing Rhubarb: M.S. Thesis. University of Wisconsin. ISBN   978-1273396984.
  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). No. 31(5), 22. APBS News September/October 2004. Archived from the original (PDF) on 2016-04-04. Retrieved 2016-10-07.
  10. ↑ "John Gray". Find a Grave. Retrieved August 24, 2019.
  11. ↑ "Hepler Family (Pelham, MA)". UmassAmherst: MassWoods. Retrieved October 6, 2016.
  12. ↑ "Kestrel Land Trust: Conserve the Valley You Love". Kestrel Land Trust. Retrieved October 6, 2016.
  13. ↑ 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 (1–4): 4–11. doi:10.1007/bf01279181. S2CID   32568416.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  14. 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. doi: 10.1111/tpj.12176 . PMID   23496242.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  15. ↑ Hepler, Peter K. (2016). "Founders' Review: The Cytoskeleton and Its Regulation by Calcium and Protons". Plant Physiology. 170 (1): 3–22. doi:10.1104/pp.15.01506. PMC   4704593 . PMID   26722019.
  16. ↑ "MBL Society Members". Marine Biological Laboratory. Retrieved October 6, 2016.
  17. ↑ "Physiology 1981". History of the Marine Biological Laboratory. Retrieved October 6, 2016.
  18. ↑ Hepler, P. K.; B. E. S. Gunning (1998). "Confocal fluorescence microscopy of plant cells". Protoplasma. 201 (3): 121–157. doi:10.1007/bf01287411. S2CID   1258312.
  19. 1 2 "AAAS Members Elected as Fellows". AAAS. Retrieved October 6, 2016.
  20. 1 2 "Members in the News". ASPB Newsletter 33(3), 26. April 2010. Archived from the original on October 9, 2016. Retrieved October 6, 2016.
  21. ↑ Hepler, P. K.; E. H. Newcomb (1967). "Fine structure of cell plate formation in the apical meristem of Phaseolus roots". Journal of Ultrastructure Research. 19 (5–6): 498–513. doi:10.1016/s0022-5320(67)80076-5. PMID   6055780.
  22. ↑ Palevitz, B. A.; 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. doi:10.1007/bf00395962. PMID   24248219. S2CID   30377452.
  23. ↑ Turgeon, R.; 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. doi:10.1007/bf00395767. PMID   24201418. S2CID   21975131.
  24. ↑ Zeiger, E.; P. K. Hepler (1976). "Production of Guard Cell Protoplasts from Onion and Tobacco". Plant Physiology. 58 (4): 492–498. doi:10.1104/pp.58.4.492. PMC   543252 . PMID   16659703.
  25. ↑ Zeiger, E., W. Moody, P. Hepler and F. Varela (1977). "Light-sensitive membrane potentials in onion guard cells". Nature. 270 (5634): 270–271. Bibcode:1977Natur.270..270Z. doi:10.1038/270270a0. S2CID   4162345.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  26. ↑ Zeiger, E.; P. K. Hepler (1977). "Light and stomatal function: blue light stimulates swelling of guard cell protoplasts". Science. 196 (4292): 887–889. Bibcode:1977Sci...196..887Z. doi:10.1126/science.196.4292.887. PMID   17821809. S2CID   13433483.
  27. ↑ Zeiger, E.; P. K. Hepler (1979). "Blue light-induced, intrinsic vacuolar fluorescence in onion guard cells". Journal of Cell Science. 37: 1–10. doi:10.1242/jcs.37.1.1. PMID   479318 . Retrieved October 6, 2016.
  28. ↑ Hepler, Peter (2005). "Calcium: An essential regulator of plant growth and development". The Plant Cell. 17 (8): 2142–2155. doi:10.1105/tpc.105.032508. PMC   1182479 . PMID   16061961.
  29. ↑ 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 (22): 8820–8824. Bibcode:1990PNAS...87.8820Z. doi: 10.1073/pnas.87.22.8820 . PMC   55051 . PMID   11607116.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  30. ↑ 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 (3): 151–155. doi:10.1002/cm.970240302.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  31. ↑ 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 (10): 1815–1824. doi:10.1105/tpc.9.10.1815. PMC   157024 . PMID   12237348.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  32. ↑ Vos, J. W., A. H. Valster and P. K. Hepler (1988). Methods for Studying Cell Division in Higher Plants. Methods in Cell Biology. Vol. 61. pp. 413–437. doi:10.1016/S0091-679X(08)61992-5. ISBN   9780125441636. PMID   9891326.{{cite book}}: CS1 maint: multiple names: authors list (link)
  33. ↑ Hepler, P. K.; J. Hush (1996). "Behavior of Microtubules in Living Plant Cells". Plant Physiology. 112 (2): 455–461. doi:10.1104/pp.112.2.455. PMC   157968 . PMID   12226402.
  34. 1 2 Lancelle, S. A., D. A. Callaham and P. K. Hepler (1986). "A method for rapid freeze fixation of plant cells". Protoplasma. 131 (2): 153–165. doi:10.1007/bf01285037. S2CID   19236616.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  35. ↑ "Poems and Quotations About the MicroWorld". Microscopy Society of America. Retrieved October 6, 2016.
  36. 1 2 Ledbetter, M. C.; K. R. Porter (1963). "A 'microtubule' in plant cell fine structure". Journal of Cell Biology. 19 (1): 239–250. doi:10.1083/jcb.19.1.239. PMC   2106853 . PMID   19866635.
  37. ↑ Newcomb, E. H. (1996). "A career in science: Fulfillment of a dream". Protoplasma. 195 (1–4): 1–3. doi:10.1007/bf01279180. S2CID   12850336.
  38. ↑ Sinnott, E. W.; R. Bloch (1945). "The cytoplasmic basis of intercellular patterns in vascular differentiation". American Journal of Botany. 32 (3): 151–156. doi:10.2307/2437535. JSTOR   2437535.
  39. ↑ Hepler, P. K.; 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. doi:10.1093/jxb/14.3.496.
  40. ↑ Green, P. B. (1962). "Mechanism for plant cellular morphogenesis". Science. 138 (3548): 1404–1405. Bibcode:1962Sci...138.1404G. doi:10.1126/science.138.3548.1404. PMID   17753861. S2CID   39081841.
  41. ↑ 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.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  42. ↑ Wasteneys, G. O.; F. Brandizzi (2013). "A Glorious Half-Century of Microtubules". The Plant Journal. 75 (2): 185–188. doi: 10.1111/tpj.12260 . PMID   23834223.
  43. ↑ Palevitz, B. A.; 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 (1): 71–93. doi:10.1007/BF00390333. PMID   24424910. S2CID   2744599.
  44. ↑ Lancelle, S. A., M. Cresti and P. K. Hepler (1987). "Ultrastructure of the cytoskeleton in freeze-substituted pollen tubes of Nicotiana alata". Protoplasma. 140 (2–3): 141–150. doi:10.1007/bf01273723. S2CID   6452268.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  45. ↑ Inoué, S.; A. Bajer (1961). "Birefringence in endosperm mitosis". Chromosoma. 12: 48–63. doi:10.1007/bf00328913. PMID   13717778. S2CID   5069716.
  46. ↑ Hepler, P. K.; W. T. Jackson (1968). "Microtubules and early stages of cell plate formation in the endosperm of Haemanthus katherinae Baker". Journal of Cell Biology. 38 (2): 437–446. doi:10.1083/jcb.38.2.437. PMC   2107485 . PMID   5664211.
  47. ↑ Hepler, P. K. (1976). "The blepharoplast of Marsilea: Its de novo formation and spindle association". Journal of Cell Science. 21 (2): 361–390. doi:10.1242/jcs.21.2.361. PMID   972175 . Retrieved October 6, 2016.
  48. ↑ Weisenberg, R. C. (1972). "Microtubule formation in vitro in solutions containing low calcium concentration". Science. 177 (4054): 1104–1105. Bibcode:1972Sci...177.1104W. doi:10.1126/science.177.4054.1104. PMID   4626639. S2CID   34875893.
  49. ↑ Hepler, P. K. (1980). "Membranes in the mitotic apparatus of barley cells". Journal of Cell Biology. 86 (2): 490–499. doi:10.1083/jcb.86.2.490. PMC   2111505 . PMID   7400216.
  50. ↑ Wick, S. M.; P. K. Hepler (1980). "Localization of Ca++-containing antimonate precipitates during mitosis". Journal of Cell Biology. 86 (2): 500–513. doi:10.1083/jcb.86.2.500. PMC   2111497 . PMID   7400217.
  51. ↑ 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 (1): 23–32. doi:10.1083/jcb.87.1.23. PMC   2110715 . PMID   7419592.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  52. ↑ Hepler, P. K.; D. A. Callaham (1987). "Free calcium increases during anaphase in stamen hair cells of Tradescantia". Journal of Cell Biology. 105 (5): 2137–2143. doi:10.1083/jcb.105.5.2137. PMC   2114859 . PMID   3680374.
  53. ↑ Hepler, P. K. (1989). "Calcium transients during mitosis: Observations in flux". Journal of Cell Biology. 109 (6): 2567–2573. doi:10.1083/jcb.109.6.2567. PMC   2115931 . PMID   2687283.
  54. ↑ 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 (1): 171–182. doi: 10.1083/jcb.111.1.171 . PMC   2116166 . PMID   2114409.
  55. ↑ 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. Bibcode:1990PNAS...87.8820Z. doi: 10.1073/pnas.87.22.8820 . PMC   55051 . PMID   11607116.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  56. ↑ 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. doi:10.1242/jcs.102.1.79 . Retrieved October 6, 2016.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  57. ↑ Palevitz, B. A., J. F. Ash, and P. K. Hepler (1974). "Actin in the green alga, Nitella". Proc. Natl. Acad. Sci. USA. 71 (2): 363–366. Bibcode:1974PNAS...71..363P. doi: 10.1073/pnas.71.2.363 . PMC   388005 . PMID   4592689.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  58. ↑ Palevitz, B. A.; 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. doi:10.1083/jcb.65.1.29. PMC   2111164 . PMID   1127014.
  59. ↑ 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. Bibcode:1976PNAS...73..165K. doi: 10.1073/pnas.73.1.165 . PMC   335861 . PMID   1061112.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  60. ↑ Hepler, P. K. (2005). "Historical Perspective Essay: Calcium: a central regulator of plant growth and development". Plant Cell. 17 (8): 2142–55. doi:10.1105/tpc.105.032508. PMC   1182479 . PMID   16061961.
  61. ↑ 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. doi:10.1242/jcs.101.1.7 . Retrieved October 7, 2016.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  62. ↑ Wilsen, K. L.; P. K. Hepler (2007). "Sperm Delivery in Flowering Plants: The Control of Pollen Tube Growth". BioScience. 57 (10): 835–844. doi: 10.1641/b571006 .
  63. ↑ 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. doi:10.1016/j.tplants.2011.10.007. PMID   22104406.
  64. ↑ Wayne, R.; P. K. Hepler (1984). "The Role of Calcium Ions in Phytochrome-mediated germination of spores of Onoclea sensibilis L.". Planta. 160 (1): 12–20. doi:10.1007/bf00392460. PMID   24258366. S2CID   14789256.
  65. ↑ Wayne, R.; P. K. Hepler (1985). "Red Light Stimulates and Increase in Intracellular Calcium in the Spores of Onoclea sensibilis". Plant Physiology. 77 (1): 8–11. doi:10.1104/pp.77.1.8. PMC   1064446 . PMID   16664033.
  66. ↑ Saunders, M. J.; P. K. Hepler (1982). "Calcium ionophore A23187 stimulates cytokinin-like mitosis in Funaria". Science. 217 (4563): 943–945. Bibcode:1982Sci...217..943S. doi:10.1126/science.217.4563.943. PMID   17747957. S2CID   24442631.
  67. ↑ Saunders, M. J.; P. K. Hepler (1981). "Localization of membrane-associated calcium following cytokinin treatment in Funaria using chlortetracycline". Planta. 152 (3): 272–281. doi:10.1007/bf00385156. PMID   24302427. S2CID   8122384.
  68. ↑ Conrad, P. A.; 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 (3): 684–687. doi:10.1104/pp.86.3.684. PMC   1054552 . PMID   16665970.
  69. ↑ Hepler, P. K., Lovy-Wheeler, A., McKenna, S. T., and Kunkel, J. G. (2006). "Ions and pollen tube growth." (PDF). The Pollen Tube. Plant Cell Monographs. Vol. 3. pp. 47–69. doi:10.1007/7089_043. ISBN   3-540-31121-1 . Retrieved August 8, 2019.{{cite book}}: CS1 maint: multiple names: authors list (link)
  70. ↑ Holdaway-Clarke, T. L., and Hepler, P. K. . (2003). "Control of pollen tube growth: Role of ion gradients and fluxes". New Phytol. 159 (3): 539–563. doi:10.1046/j.1469-8137.2003.00847.x. PMID   33873604. S2CID   86549036.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  71. ↑ Lovy-Wheeler, A., Kunkel, J. G., Allwood, E. G., Hussey, P. J., and Hepler, P. K. (2006). "Oscillatory increases in alkalinity anticipate growth and may regulate actin dynamics in pollen tubes of lily". Plant Cell. 18 (9): 2182–93. doi:10.1105/tpc.106.044867. PMC   1560910 . PMID   16920777.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  72. ↑ Feijó, J. A., Sainhas, J., Holdaway-Clarke, T., Cordiero, M. S., Kunkel, J. G., and Hepler, P. K. (2001). "Cellular oscillations and the regulation of growth: The pollen tube paradigm". BioEssays. 23 (1): 86–94. doi:10.1002/1521-1878(200101)23:1<86::AID-BIES1011>3.0.CO;2-D. PMID   11135313. S2CID   17904147.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  73. ↑ Winship, L.J., Rounds, C., and Hepler, P. K. (2017). "Perturbation analysis of calcium, alkalinity and secretion during growth of lily pollen tubes". Plants. 6 (4): 3. doi: 10.3390/plants6010003 . PMC   5371762 . PMID   28042810.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  74. ↑ Holdaway-Clark, T.L., Feijo, J.A., Hackett, G.R., Kunkel, J.G., Hepler, P. K. (1997). "Pollen tube growth and the intracellular cytosolic calcium gradient oscillate in phase while extracellular calcium influx is delayed" (PDF). Plant Cell. 9 (11): 1999–2010. doi:10.2307/3870560. JSTOR   3870560. PMC   157053 . PMID   12237353 . Retrieved August 8, 2019.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  75. ↑ Rounds, C.M., Hepler, P.K., and Winship, L.J. (2014). "The apical actin fringe contributes to localized cell wall deposition and polarized growth in the lily pollen tube". Plant Physiology. 166 (1): 139–51. doi:10.1104/pp.114.242974. PMC   4149702 . PMID   25037212.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  76. ↑ McKenna, S.T., Kunkel, J.G., Bosch, M., Rounds, C.M., Vidali, L., Winship, L.J., and Hepler, P.K. (2009). "Exocytosis precedes and predicts the increase in growth in oscillating pollen tubes". Plant Cell. 21 (10): 3026–40. doi:10.1105/tpc.109.069260. PMC   2782290 . PMID   19861555.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  77. ↑ Hepler, P.K., Rounds, C.M., and Winship, L.J. (2013). "Control of cell wall extensibility during pollen tube growth". Molecular Plant. 6 (4): 998–1017. doi:10.1093/mp/sst103. PMC   4043104 . PMID   23770837.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  78. ↑ "Jeanette Siron Pelton Award". Botanical Society of America. Retrieved October 8, 2016.
  79. ↑ "Hepler named fellow of American Society of Plant Biologists". UmassAmherst News & Media Relations. Retrieved October 6, 2016.
  80. ↑ "Peter K. Hepler". AAAS. Retrieved October 8, 2016.
  81. ↑ "Hepler wins national award for plant discoveries". UmassAmherst News & Media Relations. Retrieved October 6, 2016.
  82. ↑ "RMS Honorary Fellows". Royal Microscopical Society. Retrieved October 6, 2016.
  83. ↑ "Hepler Named Honorary Fellow of Royal Microscopical Society". UmassAmherst News & Media Relations. Retrieved October 6, 2016.
  84. ↑ "Peter K. Hepler Research Scholarship". UmassAmherst. 4 February 2016. Retrieved October 6, 2016.
  85. ↑ "Plant Biology Annual Symposium History".
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