Seorious Business: Structural Proteins In Sieve Tubes And Their Involvement In Sieve Element Occlusion [Review Article], Michael Knoblauch, Daniel R. Froelich, William F. Pickard, Winfried S. Peters
Mar 2014
Seorious Business: Structural Proteins In Sieve Tubes And Their Involvement In Sieve Element Occlusion [Review Article], Michael Knoblauch, Daniel R. Froelich, William F. Pickard, Winfried S. Peters
Winfried S. Peters
The phloem provides a network of sieve tubes for long-distance translocation of photosynthates. For over a century, structural proteins in sieve tubes have presented a conundrum since they presumably increase the hydraulic resistance of the tubes while no potential function other than sieve tube or wound sealing in the case of injury has been suggested. Here we summarize and critically evaluate current speculations regarding the roles of these proteins. Our understanding suffers from the suggestive power of images; what looks like a sieve tube plug on micrographs may not actually impede translocation very much. Recent reports of an involvement of …
Long-Distance Translocation Of Photosynthates: A Primer [Review Article], Michael Knoblauch, Winfried S. Peters
Oct 2013
Long-Distance Translocation Of Photosynthates: A Primer [Review Article], Michael Knoblauch, Winfried S. Peters
Winfried S. Peters
The storage of light energy in chemical form through photosynthesis is the key process underlying life as we know it. To utilize photosynthates efficiently as structural materials or as fuel to drive endergonic processes, they have to be transported from where they are produced to where they are needed. In this primer, we provide an overview of basic biophysical concepts underlying our current understanding of the mechanisms of photosynthate long-distance transport, and briefly discuss current developments in the field.
Forisome Performance In Artificial Sieve Tubes, Michael Knoblauch, Mike Stubenrauch, Aart J.E. Van Bel, Winfried S. Peters
Mar 2012
Forisome Performance In Artificial Sieve Tubes, Michael Knoblauch, Mike Stubenrauch, Aart J.E. Van Bel, Winfried S. Peters
Winfried S. Peters
In the legume phloem, sieve element occlusion (SEO) proteins assemble into Ca2+-dependent contractile bodies. These forisomes presumably control phloem transport by forming reversible sieve tube plugs. This function, however, has never been directly demonstrated, and appears questionable as forisomes were reported to be too small to plug sieve tubes, and failed to block flow efficiently in artificial microchannels. Moreover, plugs of SEO-related proteins in Arabidopsis sieve tubes do not affect phloem translocation. We improved existing procedures for forisome isolation and storage, and found that the degree of Ca2+-driven deformation that is possible in forisomes of Vicia faba, the standard …
Münch, Morphology, Microfluidics – Our Structural Problem With The Phloem [Review Article], Michael Knoblauch, Winfried S. Peters
Aug 2010
Münch, Morphology, Microfluidics – Our Structural Problem With The Phloem [Review Article], Michael Knoblauch, Winfried S. Peters
Winfried S. Peters
The sieve tubes of the phloem are enigmatic structures. Their role as channels for the distribution of assimilates was established in the 19th century, but their sensitivity to disturbations has hampered the elucidation of their transport mechanisms and its regulation ever since. Ernst Münch's classical monograph of 1930 is generally regarded as the first coherent theory of phloem transport, but the ‘Münchian’ pressure flow mechanism had been discussed already before the turn of the century. Münch's impact rather rested on his simple physical models of the phloem that visualized pressure flow in an intuitive way, and we argue that the …
Gfp Tagging Of Sieve Element Occlusion (Seo) Proteins Results In Green Fluorescent Forisomes, Hélène Pélissier, Winfried Peters, Ray Collier, Aart Van Bel, Michael Knoblauch
Sep 2008
Gfp Tagging Of Sieve Element Occlusion (Seo) Proteins Results In Green Fluorescent Forisomes, Hélène Pélissier, Winfried Peters, Ray Collier, Aart Van Bel, Michael Knoblauch
Winfried S. Peters
Forisomes are Ca2+-driven, ATP-independent contractile protein bodies that reversibly occlude sieve elements in faboid legumes. They apparently consist of at least three proteins; potential candidates have been described previously as ‘FOR’ proteins. We isolated three genes from Medicago truncatula that correspond to the putative forisome proteins and expressed their green fluorescent protein (GFP) fusion products in Vicia faba and Glycine max using the composite plant methodology. In both species, expression of any of the constructs resulted in homogenously fluorescent forisomes that formed sieve tube plugs upon stimulation; no GFP fluorescence occurred elsewhere. Isolated fluorescent forisomes reacted to Ca2+ and chelators …
Anisotropic Contraction In Forisomes: Simple Models Won't Fit, Winfried Peters, Michael Knoblauch, Stephen Warmann, William Pickard, Amy Shen
Mar 2008
Anisotropic Contraction In Forisomes: Simple Models Won't Fit, Winfried Peters, Michael Knoblauch, Stephen Warmann, William Pickard, Amy Shen
Winfried S. Peters
Forisomes are ATP-independent, Ca2+-driven contractile protein bodies acting as reversible valves in the phloem of plants of the legume family. Forisome contraction is anisotropic, as shrinkage in length is associated with radial expansion and vice versa. To test the hypothesis that changes in length and width are causally related, we monitored Ca2+- and pH-dependent deformations in the exceptionally large forisomes of Canavalia gladiata by high-speed photography, and computed time-courses of derived geometric parameters (including volume and surface area). Soybean forisomes, which in the resting state resemble those of Canavalia geometrically but have less than 2% of the volume, were also …
Tailed Forisomes Of Canavalia Gladiata: A New Model To Study Ca2+-Driven Protein Contractility, Winfried Peters, Michael Knoblauch, Stephen Warmann, Reinhard Schnetter, Amy Shen, William Pickard
Jun 2007
Tailed Forisomes Of Canavalia Gladiata: A New Model To Study Ca2+-Driven Protein Contractility, Winfried Peters, Michael Knoblauch, Stephen Warmann, Reinhard Schnetter, Amy Shen, William Pickard
Winfried S. Peters
Background and Aims Forisomes are Ca2+-dependent contractile protein bodies that form reversible plugs in sieve tubes of faboid legumes. Previous work employed Vicia faba forisomes, a not entirely unproblematic experimental system. The aim of this study was to seek to establish a superior model to study these intriguing actuators.
Methods Existing isolation procedures were modified to study the exceptionally large, tailed forisomes of Canavalia gladiata by differential interference contrast microscopy in vitro. To analyse contraction/expansion kinetics quantitatively, a geometric model was devised which enabled the computation of time-courses of derived parameters such as forisome volume from simple parameters readily determined …
Reversible Birefringence Suggests A Role For Molecular Self-Assembly In Forisome Contractility, Winfried Peters, Reinhard Schnetter, Michael Knoblauch
Apr 2007
Reversible Birefringence Suggests A Role For Molecular Self-Assembly In Forisome Contractility, Winfried Peters, Reinhard Schnetter, Michael Knoblauch
Winfried S. Peters
Forisomes are contractile protein bodies that control the effective diameter of the sieve elements of the faboid legumes by reversible, Ca2+-driven changes of shape. Forisomes consist of fibrils; we inferred from available electron-microscopical data (which necessarily provide images of fixed, non-functional forisomes) that a reversible assembly of ordered fibrillar arrays might be involved in the contractile mechanism. Here we examined functional forisomes isolated from Vicia faba L. by differential interference contrast microscopy and polarisation microscopy. We found them birefringent in the longitudinally expanded but not in the contracted state, showing ‘parallel extinction’ with the direction of vibration of the slow …
The Geometry Of The Forisome–Sieve Element–Sieve Plate Complex In The Phloem Of Vicia Faba L. Leaflets, Winfried Peters, Aart Van Bel, Michael Knoblauch
Jul 2006
The Geometry Of The Forisome–Sieve Element–Sieve Plate Complex In The Phloem Of Vicia Faba L. Leaflets, Winfried Peters, Aart Van Bel, Michael Knoblauch
Winfried S. Peters
Forisomes are contractile protein bodies that appear to control flux rates in the phloem of faboid legumes by reversibly plugging the sieve tubes. Plugging is triggered by Ca2+ which induces an anisotropic deformation of forisomes, consisting of a longitudinal contraction and a radial expansion. By conventional light microscopy and confocal laser-scanning microscopy, the three-dimensional geometry of the forisome–sieve element–sieve plate complex in intact sieve tubes of leaflets of Vicia faba L. was reconstructed. Forisomes were mostly located close to sieve plates, and occasionally were observed drifting unrestrainedly along the sieve element, suggesting that they might be utilized as internal markers …
Forisome Based Biomimetic Smart Materials, Amy Shen, Benjamin Hamlington, Michael Knoblauch, Winfried Peters, William Pickard
Jun 2006
Forisome Based Biomimetic Smart Materials, Amy Shen, Benjamin Hamlington, Michael Knoblauch, Winfried Peters, William Pickard
Winfried S. Peters
With the discovery in plants of the proteinaceous forisome crystalloid (Knoblauch, et al. 2003), a novel, non-living, ATP-independent biological material became available to the designer of smart materials for advanced actuating and sensing. The in vitro studies of Knoblauch, et al. show that forisomes (2-4 micron wide and 10-40 micron long) can be repeatedly stimulated to contract and expand anisotropically by shifting either the ambient pH or the ambient calcium ion concentration. Because of their unique abilities to develop and reverse strains greater than 20% in time periods less than one second, forisomes have the potential to outperform current smart …
Prospective Energy Densities In The Forisome, A New Smart Material, William Pickard, Michael Knoblauch, Winfried Peters, Amy Shen
Dec 2005
Prospective Energy Densities In The Forisome, A New Smart Material, William Pickard, Michael Knoblauch, Winfried Peters, Amy Shen
Winfried S. Peters
The forisome is a protein structure of plants which, in low Ca2+ solutions, assumes a crystalline condensed conformation and, at high Ca2+, swells to a dispersed conformation; this transition has been attributed to electrostatic deformation of protein “modules”. Forisomes could become an important smart material if the energy density of transformation approached 1 MJ m−3. Quantitation of the forisome as a charged porous continuum permeated by electrolyte fails by orders of magnitude to achieve this energy density electrostatically. However, condensed → dispersed transitions can be visualized alternatively: (i) an ionic bond near the surface of a forisome crystal dissolves to …
Forisomes, A Novel Type Of Ca2+-Dependent Contractile Protein Motor [Review Article], Michael Knoblauch, Winfried Peters
Apr 2004
Forisomes, A Novel Type Of Ca2+-Dependent Contractile Protein Motor [Review Article], Michael Knoblauch, Winfried Peters
Winfried S. Peters
This paper has no abstract; this is the first paragraph. Motility of cell components in both animal and plant cells is mostly based on the movement of motor proteins along actin filaments or microtubules [Boal, 2002]. The dominance of ATP hydrolysis as the energy source for such movements is so complete, that modern textbooks define “motor proteins” as nucleoside triphosphate-dependent actuators [e.g., Alberts et al., 2002]. In only one known case, a reversible mechanism of cell motility is driven by the interaction of Ca2+ and the responsive protein(s). Some sessile ciliates control the effective length of their stalk by means …
Atp-Independent Contractile Proteins From Plants, Michael Knoblauch, Gundula Noll, Torsten Müller, Dirk Prüfer, Ingrid Schneider-Hüther, Dörte Scharner, Aart Van Bel, Winfried Peters
Aug 2003
Atp-Independent Contractile Proteins From Plants, Michael Knoblauch, Gundula Noll, Torsten Müller, Dirk Prüfer, Ingrid Schneider-Hüther, Dörte Scharner, Aart Van Bel, Winfried Peters
Winfried S. Peters
This paper has no abstract; this is the first paragraph. Emerging technologies are creating increasing interest in smart materials that may serve as actuators in micro- and nanodevices. Mechanically active polymers currently studied include a variety of materials. ATP-driven motor proteins, the actuators of living cells, possess promising characteristics, but their dependence on strictly defined chemical environments can be disadvantagous. Natural proteins that deform reversibly by entropic mechanisms might serve as models for artificial contractile polypeptides with useful functionality, but they are rare. Protein bodies from sieve elements of higher plants provide a novel example. sieve elements form microfluidics systems …
Reversible Calcium-Regulated Stopcocks In Legume Sieve Tubes, Michael Knoblauch, Winfried Peters, Katrin Ehlers, Aart Van Bel
Apr 2001
Reversible Calcium-Regulated Stopcocks In Legume Sieve Tubes, Michael Knoblauch, Winfried Peters, Katrin Ehlers, Aart Van Bel
Winfried S. Peters
Sieve tubes of legumes (Fabaceae) contain characteristic P-protein crystalloids with controversial function. We studied their behavior by conventional light, electron, and confocal laser scanning microscopy. In situ, crystalloids are able to undergo rapid (<1>sec) and reversible conversions from the condensed resting state into a dispersed state, in which they occlude the sieve tubes. Crystalloid dispersal is triggered by plasma membrane leakage induced by mechanical injury or permeabilizing substances. Similarly, abrupt turgor changes imposed by osmotic shock cause crystalloid dispersal. Because chelators generally prevent the response, divalent cations appear to be the decisive factor in crystalloid expansion. Cycling between dispersal and …
