and move along the raphe, carrying the particles along the raphe. If the raphe fluid adheres to a large object or a substrate, the diatom moves in the opposite direction [14.122]. As the raphan comes into contact with water, it hydrates, can no longer wet the raphe, and exits to the medium. The diatom trail is analogous to the flame of a candle. (b) “The capillarity model for diatom gliding locomotion, as originally conceived in [14.122]. A schematic ‘longitudinal slice’ of a single raphe is shown as if the raphe went straight through the silica valve. (It is actually hooked in cross section.) The crystalloid bodies empty their fibrillar, mucopolysaccharide contents into the raphe via exocytosis. The role of the microfilaments was speculated to be control of the distribution of the exocytosis along the raphe in an unspecified manner. The directionality of the motion could come either from an asymmetric distribution of release of mucopolysaccharide along the raphe, or, as shown here, from a postulated difference in rate of hydration of the mucopolysaccharide between the leading and trailing pores. The hydration of the mucopolysaccharide may also permit it to stick to the substratum, as indicated. This results in motion in the direction shown. The released, fully hydrated mucopolysaccharide stays attached to the substratum as trail material. While capillarity fills the raphe with the mucopolysaccharide, its hydration removes it and provides the driving force. (Hydrated mucopolysaccharide no longer wets the walls of the raphe, suggested to consist of a hydrophobic lipid layer by [14.92]” [14.117] (reprinted with permission of Elsevier). The sketch has been rotated and aligned to correspond to the candle. If the substrate were replaced by small particles, they would rise upwards just as the liquid wax does in a candle. The sketch has been modified to show how the microfilament bundles may permit access of the crystalloid bodies [14.79] at one end of the raphe but not the other, by sliding along their length. Note: “We have electron micrographic evidence that indeed these vesicles are secreted into the raphe canal” [14.47]. In this model, the motile pennate diatom is the flame of life.Figure 14.19 Bellowing diatoms (1887). Left: Stauroneis baileyi, shown in girdle view, was found to bellow out, with the distance between a and b increasing, when moving in the direction of the arrow [14.342]. Right: A selfcompressing bellows, on blowing air out, would move in the same direction [14.106] (public domain image).Figure 14.20 Top: In 1896: Cross sections of the pennate diatom Pinnularia major from the middle to the end of the cell showing how the raphe is a slit through the whole valve [14.205]. Bottom: Robert Lauterborn in 1928 [14.239] (reprinted with permission of Elsevier).Figure 14.21 Jelly powered jet skiing diatoms (1896). In 1892: “… Pinnularia nobilis in motion in the view on the girdle side. n the nucleus, c the centrosome, x the peculiar double threads in the plasma, a the inflow to the node (k) of the anterior raphe, b the gelatin thread that shoots out to the rear, which has rolled up at the right end at the end. The arrows indicate the direction of movement of the diatom, the inflow and the thread” (translated from [14.44]). Otto Bütschli (1848-1920) [14.418] attributed the diatom’s motion to pulling, pushing and recoil of the threads, rather than the inward flow he thought he observed. (Photograph of Bütschli by Max Kögel [14.191] with permission of Universitätsbibliothek Heidelberg under the Creative Commons Attribution-Share Alike 4.0 International license).Figure 14.22 Bubble powered diatoms (1905). Left: The bubbly motile diatom. Middle: Nitzschia acicularis [14.368]. Right: View of a portion of the Chemical Laboratory at the Mt. Prospect Laboratory of the Brooklyn Water Works, next door to the Biological Laboratory, where Daniel D. Jackson [14.80] worked [14.403].Figure 14.23 Diatoms win: “I have no new theory to offer and see no reason to use those already abandoned” (1940) [14.230]. Left: Medical botanist Pierre Martens (1895-1981) in 1950 [14.73]. Right: Martens’ depiction of Otto Müller’s flow model: “Connective view of a valve, showing the channeling at the level of the median nodule and the paths attributed to the propellant currents. The median nodule is drawn (after Müller), in an orientation which does not show the outlet of the ‘external slit’ outside; the internal structure of the polar nodules is not shown. The upper arrow indicates the direction of locomotion…. Abbreviations: np = polar nodule; nc = central nodule; fe = external slot of the raphe; fi = internal slot; rc = groove of the central nodule, joining the two internal slots of the same valve; cu = small channel joining the external and internal slits”13 [14.230].Figure 14.24 Is diatom motility a special case of cytoplasmic streaming? (1943). Left: Early model of what we now call a motor protein invoked for cytoplasmic streaming. 1) Protein molecule in extended form. Bond at anterior end of molecule. (2) Protein molecule in contracted form. (3) Shifting of bond from anterior to posterior end. (4) Protein molecule in expanded form…. Let us say that the molecules which form bonds in this way so as to contribute to the motion are in phase and those which may form bonds so as to oppose the motion are out of phase. It is clear that streaming can occur only when the number of molecules in phase exceeds those out of phase. This cannot happen by chance alone and we must therefore postulate that some mechanism is present which sets the majority of stream proteins in phase. This mechanism must of course be intimately related to the mechanism responsible for the reversal of streaming” [14.222] (reprinted with permission of the American Philosophical Society). Right: Motion of an inchworm caterpillar [14.287] (reprinted with permission of Elsevier).Figure 14.25 “Row, row, row your boat. The molecular motors in the myosin heads pull the myosin filaments (blue) over the actin filaments” [14.157]. This version from [14.46] (reprinted with permission of Cambridge University Press). Cf. Figure 14.11.Figure 14.26 Model for an amoeba (1999) [14.10] (reprinted with permission of Elsevier).Figure 14.27 In 2004: “A schematic representation of a likely mechanism underlying the fluctuation enhancement of an actin filament, induced by Chara myosin molecules. (a) Disequilibrating state: A myosin head generating the sliding force influences the kinetics of the neighboring heads along the actin filament, in which either the pushing or the pulling force is generated. (b) Coordinating state: These activated heads develop a coordination among themselves along the filament. Coordination in one place then induces a disequilibrium out of coordination in the neighborhood. Equilibration and desequilibration thus reiterate” [14.144] (reprinted with permission of Elsevier).Figure 14.28 “Schematic picture of the delivery of different cell wall components to the plant plasma membrane…. Question marks indicate that no direct experimental evidence for the localisation of the component is available…. The vesicles containing the CESAs [cellulose synthase proteins] are transported to the plasma membrane with the help of actin cables” [14.111] (reprinted with permission of Elsevier). A myosin XI such as in the class of those involved in cytoplasmic streaming functions in cellulose exocytosis [14.441].Figure 14.29 Top left: “L.S. [lateral section] in valve view (Navicula cuspidata) showing detail of microfilamentous bundles and associated vesicles; some vesicles appear attached to the bundles (arrow). Scale = 1 µm” [14.93] (reprinted with permission of Elsevier). These are presumed to carry raphe fibrils (raphan). Top right: An F-actin = filamentous actin = microfilament can carry secretory vesicles to the cell membrane [14.337]. In this depiction, transport of vesicles can be either by direct attachment to myosin or indirectly via hydrodynamic flow [14.42] (reprinted with permission of John Wiley & Sons). The attachment of myosin to a vesicle may involve “membrane-anchored core myosin receptors, possibly aided by adaptors” [14.279]. Myosin XI/vesicle attachments are transient, lasting only a few seconds [14.30]. Middle left: An explicit model for binding of myosin to a membrane, in this case the outer (ONM) and inner (INM) nuclear membranes [14.442] (reprinted with kind permission of Iris Meier). Bottom: “The microfilament model for diatom gliding locomotion, as conceived by Edgar & Pickett-Heaps (1984) [14.93], and adapted from their Figures 39, 40 and 41. All features are the same as in [Figure 14.18], except that: (a) the mucopolysaccharide fibrils are assumed to be attached to the microfilament bundles through the plasmalemma, which has no effect because of its fluid nature, via “the lining of the vesicles [crystalloid bodies] in which the strands were originally synthesized”; (b) hydration is assumed to occur along the whole length of each mucopolysaccharide fibril while it is still within the raphe; (c) the fibrils are assumed to swell and elongate as they come out of the crystalloid bodies; (d) a mechanism is needed by which “the mucilage strands are broken free from the plasmalemma on reaching the apical raphe ending [trailing pore].” The microfilament bundle is presumed to provide the motive force. Reversal of the direction of motion is suggested to occur as follows: “Since... there are two bundles of filaments..., perhaps the actin filaments in each bundle are oriented in one direction, and the polarities in the two bundles of filaments are opposite. If this were so, bidirectional movement could be envisaged as occurring as...the raphe
