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Notes: Summary Dinitrophenol and deoxyglucose (DNP/DOG) were used to investigate the effects of ATP depletion on mitotic PtK1 cells. Direct determination of cellular ATP levels showed that the drop of ATP induced by DNP/DOG was rapid; recovery to normal ATP levels was equally rapid once DNP/DOG was removed. On addition of DNP/DOG to live cells, cytoplasmic activity ceased; interphase and prophase cells showed little other response to DNP/DOG. During prometaphase, DNP/DOG induced a pronounced movement of oscillating, monopolar chromosomes towards the spindle poles. As chromosomes became bipolarly attached, DNP/DOG caused the spindle poles themselves to move together. By metaphase, DNP/DOG-treatment led to significant shortening of the spindle which remained intact. DNP/DOG rapidly stopped anaphase chromosome movement and cytokinesis. Nocodazole (NOC) caused the rapid breakdown of the mitotic spindle; prometaphase chromosomes clustered at the poles and in metaphase cells, the poles were drawn towards the chromosomes as the spindle became disorganized. When cells were pretreated with DNP/DOG and then NOC/DNP/DOG, nocodazole did not break down the spindle. When nocodazole was applied first to break down spindle MTs then DNP/DOG was added to the nocodazole, a second contraction was often induced by the DNP/DOG in the absence of spindle microtubules (MTs). Chromosomes expanded appreciably outwards from the poles when the DNP/DOG was removed, even when the cells remained in nocodazole.

Notes: Summary Cells of the centric diatomDitylum brightwellii were filmed undergoing cell division and valve secretion, and were fixed for transmission electron microscopy. Attention was directed particularly at the origin of the Labiate Process Apparatus (LPA). As reported previously (li andVolcani 1985 a), the nucleus, centrally situated during interphase, moves laterally to undergo mitosis against the girdle bands. We describe the spindle which splits up into numerous fibres of overlapped polar microtubules (MTs) by metaphase. The chromosomes are diffuse and the spindle elongates rapidly during anaphase. A complex of organelles is found at the poles and ill-defined, dense material extends to the nearby plasmalemma from prophase on. The two Silica Deposition Vesicles (SDVs) are initiated during anaphase close to the poles and by midcleavage, the dense LPA arises on each SDV close to dense polar material. After cleavage, the daughter protoplasts round up and the SDV, already containing a nascent valve, expands over the cleavage furrow. The labiate process, a long straight hollow tube of silica, is rapidly (ca. 25 minutes) secreted from directly under the LPA; a fibrous plug (polysaccharide?) always appears in the SDV immediately adjacent to the LPA during the initiation of this secretion. The ill-defined Microtubule-Organizing Center (MC) from the spindle pole remains close to the LPA and in it can be seen the tiny presumptive primordial spindle on the nuclear envelope. The raphe and the labiate process (LP), both highly differentiated apertures in the valve, probably function in a specialized form of the mucilage secretion involved in generation of movement in raphid diatoms, and in a simple form of movement in some centrics. Morphogenesis of the LP is associated with the LPA while differentiation of the raphe is almost associated with the MC; both MC and LPA have an intimate ontological relationship with the spindle pole and the postmitotic cytoskeletal system of MTs. This association also is seen in the formation of the LP in an araphid pennate,Diatoma (work in progress). Therefore, from functional, morphogenetic and ontogenetic observations, we support the proposal that the raphe of pennate diatoms arose from the LP of centric diatoms.

Notes: Summary InChaetoceros peruvianus, the two very long, delicately tapered setae (spine-like processes) of the “lower” valve curve downwards gently until they are often almost parallel, while those emerging from the “upper” valve curve sharply downwards until oriented almost in the same direction as the setae of the lower valve. This curvature creates a deep pit between the bases of the upper valve's setae, where they emerge from the valve. In live cells, extension of setae is rapid and very sensitive to disturbance. After cleavage the new silica deposition vesicle (SDV) appears in the centre of the furrow and expands outwards over it. A distinct microtubule centre (MC) appears directly on top of the SDV. Microtubules (MTs) from the MC ensheath the nucleus, and others fan out over the SDV and plasmalemma. A little later, the MC in the lower daughter cell moves off the SDV, and its MTs now appear to mould the plasmalemma/ SDV into the deep pit between the base of the setae. In the upper daughter cell, the MC remains on the SDV. Initiation of setae is first observed as protuberances of bare cytoplasm growing from the sides of the daughter cells, through gaps in the parental valve. Many MTs initially line the plasmalemma of these protuberances as they grow outwards and the SDV also expands over the new surface. As the setae get longer, a unique complex of three organelles appears. Just behind the naked cytoplasm at the tip of the seta, a thin flat layer of fibrous material lines the plasmalemma. This, the first of the complex, is called the “thin band”. Immediately behind this is the second, a much thicker, denser fibrous band, the “thick band”. At the front edge of the SDV, 5–6 “finger-like outgrowths” of silicified wall grow forwards. These are interconnected by the elements of the thick band which thus apparently dictate the polygonal profile of the seta. These also appear to generate the spinules (tiny spines) that adorn the surface of the seta; the spiral pattern of the spinules indicates that this whole complex might differentiate one after the next, in order. Further back from the tip, evenly spaced transverse ribs are formed. These are connected to the third organelle in the complex, the “striated band”; our interpretation is that the striated band sets up the spacing of the ridges that regularly line the inner surface of the setae. During seta growth, this complex is apparently responsible for controlling the delicate tapering curvature of the very fine silica processes. Since the complex is always seen near the tip of the seta, we conclude that it migrates forwards steadily as the tip grows. While the thin and thick bands could slide continuously over the cell membrane, the striated band must be disassembled and then recycled forward during extension if it is indeed connected to the ridges lining the inside of the setae. We could find no indication that turgor pressure drives extension of the setae, in which event the activity of these organelles is responsible for growth using the justformed silica tube as the base from which extension is generated.

Notes: Summary An early paper demonstrating the existence of fibrils (microtubules) within the flagellum is summarised. The paper appears the first to have demonstrated the existence of flagellar microtubules using electron microscopy, and it has been neglected in the literature.

Notes: Summary The “Pac-Man” model for explaining chromosome movement is based on three main tenets: (i) the force that moves chromosomes is generated at the kinetochore; (ii) disassembly of the microtubules (MTs) of the kinetochore fibre generates poleward movement; and (iii) the energy required for this movement comes from MT disassembly. We show that these tenets are not valid in some and perhaps many situations. Thus, the Pac-Man model is inadequate and misleading as the central basis for explaining chromosomal motion generally. We argue that multiple mechanisms are involved in mitotic function and that a contractile/elastic spindle matrix is likely involved not only in anchoring kinetochore fibres, but also by exerting force on them. This view of the spindle matrix shares some features with the “tensegrity” model already formulated as a basis for understanding interphase cell behaviour.

Notes: Summary The paper summarises results of simple radioautographic experiments using tritiated glucoses to investigate wall secretion in plant cells. In outer root cap cells, labelled material was first concentrated in the Golgi bodies; it later appeared in vesicles, and was incorporated into the wall immediately under the plasmalemma. It finally collected mainly in the slime layer surrounding the root tip. Biochemical analyses have indicated that this material was pectic in nature. In inner root cap and epidermal cells, labelled material incorporated into the walls and also the cell plates of dividing cells was also apparently mainly derived from Golgi bodies. In meristematic (less differentiated) cells, however, the endoplasmic reticulum was more frequently labelled than the Golgi bodies near walls that had incorporated derivatives of labelled glucose. Considerable incorporation of labelled derivatives into the wall thickenings in coleoptile xylem cells was often detected; nearby elements of the endoplasmic reticulum were again frequently labelled in these cells and less often, Golgi bodies and the cytoplasm in the region occupied by microtubules contained radioactivity. Labelling of starch grains in the plastids was generally observed, but not in cells secreting large amounts of wall materials (outer root cap and older xylem cells); however, addition of larger amounts of exogenous glucose to outer root cap cells, following their incubation in tritiated glucose, promoted such incorporation. The paper finally sets forth some considerations on experimental techniques for radioautography that might be of more general application.

Notes: Summary Tritiated leucine, tyrosine, phenylalanine, methyllabelled methionine, and cinnamic acid were used to study xylem wall deposition and lignin formation with radioautography. Leucine did not specifically label xylem thickenings; tyrosine, phenylalanine and methionine were quite good precursors in this regard. Cinnamic acid was also readily taken up by the tissues and was very markedly concentrated in the xylem thickenings; the labelling of thickenings also occurred in empty tracheids. In developing xylem cells, labelling of the cytoplasm indicated that both the endoplasmic reticulum and Golgi bodies were associated with the wall incorporation. Vesicles probably derived from the Golgi bodies, were generally observed to aggregate in the cytoplasm near the bands of wall microtubules (even if secondary wall thickening had not commenced). Simple biochemical analyses showed that incorporation of cinnamic acid into amino acids and proteins was negligible, but some lignin oxidation products were heavily labelled. The results are related to the biochemistry of lignin synthesis, and confirm that cinnamic acid is a highly specific marker for some forms of wall synthesis.

Notes: Summary Emergence of zoospores ofOedogonium and their subsequent developmental changes have been studied using live material and sections prepared for light and electron microscopy. Release commences with rupture of the cell wall at its pre-weakened site near the apical caps. The pliable protoplast of the zoospore becomes completely spherical once free of the wall; it is enclosed within the hyaline vesicle which expands continuously and then disappears. Meanwhile, as the flagella become active, the zoospore begins to elongate and its dome starts to protrude from a circular constriction where the flagella are inserted. Once free of the hyaline vesicle, it is actively motile for a variable period, during which elongation continues. The motile phase ceases when the zoospore begins to vibrate, whereupon the flagella are all violently shed. Soon after this, the constriction disappears from around the dome which becomes more pointed; the immobile cell now elongates further, increasing in volume. The cell periphery contains numerous contractile vacuoles. Zoospore elongation may be associated with a proliferation of longitudinal microtubules, and once the flagella are shed, the flagellar rootlet system disintegrates, probably releasing the rootlet microtubules. Mechanisms involved in the release of the zoospore are also discussed.

Notes: Summary Differentiation of immobile zoospores into future basal cells of vegetative filaments ofOedogonium is described. Once flagella are shed, the constriction disappears from around the dome which soon starts pushing out rhizoid(s); these may become long and/or numerous if cells cannot attach themselves to a substrate. The flagellar apparatus, including the basal bodies, slowly disintegrates within the dome without involving lysosomal structures. A wall is secreted around the elongating cell; several distinguishable types of vesicular components are discharged into it at the dome. Some are derived from hypertrophied golgi bodies, and others from the numerous basal particles (characteristic of zoospores) which had undergone changes in appearance and cytochemical reactivity. The growing rhizoids flatten and extend, finger-like, across the surface of flat substrates, or wrap around vegetative filaments of other alga. The thick holdfats wall is secreted around them, usually forming a structure like a flattened cone; meanwhile the holdfast's interior containing much endoplasmic reticulum becomes increasingly subdivided into a labyrinth by ingrowing folds of wall. Microtubules and extensive arrays of smooth reticulate membranes are present near these walls. The hypertrophied golgi bodies in the holdfast soon revert to their usual smaller size. Eyespots degenerate, and the apical wall develops the circumferential discontinuity which will be the site of the future ring. In unattached germlings, the large accumulation of rough endoplasmic reticulum in the holdfast often shows evidence of breakdown, being replaced by masses of smooth membranes or else homogeneous “souplike” cytoplasm devoid of membranes.

Notes: Summary Cell division in germlings and young filaments ofOedogonium is described. In one species, division proceeded as expected. The ring was formed at the apical wall weakening, and the basal cell did not divide again; the cap of wall derived from the basal cell was sometimes incorporated into the wall of the new apical cell. The second species showed significant differences. The “ring” laid down in the single-celled germling, and sometimes in the apical cell of a two-celled filament covered the whole apical end wall; the basal cell also usually underwent one more division, utilizing a normal ring. It is suggested that the formation of rings for cell division represents an adaptation of a wound-response mechanism, brought into action by the deliberate creation of the circumferential weakening in the apical cell wall, and a concurrent increase in cell turgor. This proposal helps explain the divergent results above, and is further supported by the following examples, given in the paper: a) the frequent occurrence of accidental breaks in the wall, repaired sequentially by the deposition of amorphous and then layered wall material; b) a similar localized wall reinforcement invoked by the presence of rhizoids of other holdfasts attaching themselves to vegetative cells; c) a continuous layer of ring material being deposited over the entire end wall of a dividing cell, when the adjacent apical cell was empty; and d) the deposition of two rings in cells that had been previously treated with colchicine to prevent cytokinesis, and then been allowed to divide again.