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Ultrastructural basis of mitosis in the fungusNectria haematococca (sexual stage ofFusarium solani) (1991)

Jensen, C. G. ; Aist, J. R. ; Bayles, C. J. ; [et al.]

Springer

Protoplasma 161 (1991), S. 137-149

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ISSN: 1615-6102

Keywords: Aster ; Bridge ; Fungus ; Microtubule ; Mitosis ; Spindle

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary Previous studies have shown that in the fungusNectria haematococca (the sexual stage ofFusarium solani f. sp.pisi), the central spindle regulates the rate at which the asters pull apart the spindle pole bodies (SPBs) during anaphase B. These controlled movements are likely to be dependent upon lateral interactions between the microtubules (MTs) of both the central spindle and the asters. Since molecular bridges between MTs are known to play structural and motive roles in MT-based activities, such bridges are likely to be present in both of these areas of the mitotic apparatus. Therefore, in this study we have examined the potential for bridging between MTs, and the arrangement of intermicrotubule bridges in the mitotic apparatus ofN. haematococca. Using three-dimensional reconstruction analysis of serial thin sections, we found that 70% of the MTs in anaphase A central spindles, 902–100% in anaphase B spindles, and an average of 46% of astral MTs were sufficiently close to each other (i.e., within 70 nm center-to-center) for bridging to occur. Structures resembling intermicrotubule bridges were seen in electron micrographs between parallel MTs of both the central spindle and the asters. Microdensitometer-computer correlation analysis of the putative bridges identified them as having a nonrandom arrangement along the MT that was compatible with a 14-dimer helical superlattice. Intermicrotubule bridges in the anaphase B central spindle could: (i) enhance its strength by bundling the MTs, (ii) stabilize a portion of the MTs against depolymerization, thereby allowing the spindle to persist to an advanced stage of elongation, and (iii) generate forces within the spindle that counter the pull of the asters, thus regulating the rate of spindle elongation. In the aster, intermicrotubule bridges could increase the amount of astral pulling force applied to the SPB by (i) generating intertubule motive forces and/or (ii) enlarging the functional domain of the aster through structural linkages between polar MTs and free MTs.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01322726

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Division, growth, and branch formation in protonema of the mossPhyscomitrium turbinatum: Studies of sequential cytological changes in living cells (1981)

Jensen, L. C. W.

Springer

Protoplasma 107 (1981), S. 301-317

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ISSN: 1615-6102

Keywords: Apical cell ; Cell elongation ; Cell polarity ; Chloroplast replication ; Physcomitrium

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary Elongating caulonemal tip cells ofPhyscomitrium turbinatum were cultivated on mediumcoated cover slips and periodically observed with Nomarski differential interference contrast optics. Tip cells exhibit apical growth and an average growth rate of 27.5 μm/h. During cell elongation the nucleus migrates forward in the tip cell, but this movement slowly decreases so that there is a gradual increase in the distance between the nucleus and cell tip. Minimum length cells contain small vacuoles adjacent to the basal wall which coalesce during subsequent cell elongation to form a solitary large basal vacuole. An increase in chloroplasts during cell elongation is due to the presence of a population of proliferating chloroplasts located between the cell tip and the nucleus resulting in a gradient in chloroplast number and shape. The zone of chloroplast proliferation shifts progressively forward during cell elongation from a peri-nuclear position to a region closer to the cell tip. During division of the apical cell a perpendicular metaphase plate is formed. Reorientation movements of the phragmoplast-cell plate during telophase, and early stages of the following interphase produce a 35–40° cross wall. This rotation of the spindle axis positions the daughter nuclei temporarily adjacent to the lateral walls on opposite sides of the cell with the sub-apical nucleus on the side nearest the light source. It subsequently migrates across the cell to become situated on the wall farthest from the light source. Sub-apical cells form branches at the distal (= apical) end of the cell on the lateral wall closest to the light source. Branch development is accompanied by changes in chloroplast shape, number, and position.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01276832

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Fine structure of protonemal apical cells of the mossPhyscomitrium turbinatum (1984)

Jensen, L. C. W. ; Jensen, C. G.

Springer

Protoplasma 122 (1984), S. 1-10

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ISSN: 1615-6102

Keywords: Invaginated mitochondria ; Moss protonema ; Organelle gradients ; Vacuole formation

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary Elongating caulonemal apical cells of the mossPhyscomitrium turbinatum were cultivatedin vitro and observed during successive stages of cell elongation and division. Actively-growing cells which had completed approximately half of their growth in length were examined by electron microscopy. The distribution of many organelles changes progressively from the cell tip to the distal edge of the large basal vacuole, establishing an apical-basal gradient in organization. Whereas the vacuoles become progressively more extensive in more mature parts of the cell, the dictyosomes, chloroplasts and smooth endoplasmic reticulum are more numerous in younger regions. Some mitochondria in the younger regions of the cell contain localized areas of membrane invagination. Attempts were made to clarify the origin and growth of vacuoles, which become increasingly prominent as the apical cell elongates. Morphological evidence suggests that vacuoles arise in close association with endoplasmic reticulum and dictyosomes as a result of ER dilation and/or cytoplasmic sequestration. The number of vacuolar profiles is highest at the cell tip, decreasing progressively toward the base of the cell, Conversely, the mean area of vacuolar profiles increases progressively toward more basal regions of the cell. These features, along with the increasing number of closely grouped vacuolar profiles along an apical-basal gradient are compatible with the concept of vacuolar growth by coalescence, culminating in their union with the basal vacuole.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01279432

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