THE SIGNIFICANCE OF THE CAMBIUM IN THE STUDY OF CERTAIN PHYSIOLOGICAL PROBLEMS

1. The adjacent, undifferentiated, uninucleated cells of the lateral meristem or cambium are of two distinct shapes and sizes: (1) small, more or less isodiametric initials which are of the same general order of magnitude as the cells of the terminal meristem and embryo; and (2) large, elongated initials which in certain cases may attain a length of more than 10,000 micra and a volume of 10,000,000 cubic micra. The large initials may be induced to divide to form small initials, and the latter to regenerate elongated cells of normal dimensions. Thus, the cambium affords an unusually favorable medium for the study of a number of fundamental physiological and cytological problems. 2. A study of the cambium reveals the fact that there is a very-much greater variability in the size of meristematic cells in plants than was suspected by Sachs or Strasburger, and that the working sphere of the nucleus is by no means so restricted as assumed by these investigators. 3. Although the larger cambial initials of Pinus strobus tend to have larger nuclei, the nucleocytoplasmic-relation varies within wide limits and the diploid number of chromosomes is constant. The conditions in the cambium do not support Winkler's view that there is a close correlation between chromosomal number (chromosomal mass) and cell size in the somatic tissue of plants, and that giant cells are hyperchromatic. 4. The process of cell plate formation in the cambium is a remarkable phenomenon, and one which is significant in discussing the relative merits of various theories concerning the dynamics of karyokinesis and cytokinesis. 5. The newly formed partition membranes in the cambial initials frequently intersect the side walls at angles of varying degrees of acuteness, which is in contradiction to Errera's (Plateau's) Law of Minimal Area.

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Dynamics and roles of phragmoplast microfilaments in cell plate formation during cytokinesis of tobacco BY-2 cells

Science Bulletin ◽

10.1007/s11434-009-0265-5 ◽

2009 ◽

Vol 54 (12) ◽

pp. 2051-2061 ◽

Cited By ~ 3

Author(s):

Yan Zhang ◽

WenJie Zhang ◽

Frantisek Baluska ◽

Diedrik Menzel ◽

HaiYun Ren

Keyword(s):

Cell Plate ◽

Cell Plate Formation ◽

Plate Formation

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Diversification of sterol methyltransferase enzymes in plants and a role for β-sitosterol in oriented cell plate formation and polarized growth

The Plant Journal ◽

10.1111/tpj.13043 ◽

2015 ◽

Vol 84 (5) ◽

pp. 860-874 ◽

Cited By ~ 15

Author(s):

Masatoshi Nakamoto ◽

Anne-Catherine Schmit ◽

Dimitri Heintz ◽

Hubert Schaller ◽

Daisaku Ohta

Keyword(s):

Cell Plate ◽

Polarized Growth ◽

Cell Plate Formation ◽

Plate Formation ◽

Sterol Methyltransferase

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Very-long-chain fatty acids are required for cell plate formation during cytokinesis in Arabidopsis thaliana

Journal of Cell Science ◽

10.1242/jcs.074575 ◽

2011 ◽

Vol 124 (19) ◽

pp. 3223-3234 ◽

Cited By ~ 37

Author(s):

L. Bach ◽

L. Gissot ◽

J. Marion ◽

F. Tellier ◽

P. Moreau ◽

...

Keyword(s):

Fatty Acids ◽

Arabidopsis Thaliana ◽

Cell Plate ◽

Long Chain Fatty Acids ◽

Cell Plate Formation ◽

Plate Formation ◽

Long Chain ◽

Chain Fatty Acids

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Constrained Optimization of Multi-Degree-of-Freedom Mechanisms for Near-Time Optimal Motions

22nd Biennial Mechanisms Conference: Mechanism Design and Synthesis ◽

10.1115/detc1992-0343 ◽

1992 ◽

Author(s):

Satish Sundar ◽

Zvi Shiller

Keyword(s):

Constrained Optimization ◽

Design Method ◽

Close Correlation ◽

Optimization Methods ◽

Pattern Search ◽

Degree Of Freedom ◽

Design Parameters ◽

Maximum Acceleration ◽

Time Optimal ◽

Order Of Magnitude

Abstract This paper presents a design method of multi-degree-of-freedom mechanisms for near-time optimal motions. The design objective is to select system parameters, such as link lengths and actuator sizes, so as to minimize the optimal motion time of the mechanism along a given path. The exact time optimization problem is approximated by a simpler procedure that maximizes the acceleration near the end points. Representing the directions of maximum acceleration with the acceleration lines, and the reachability constraints as explicit functions of the design parameters, we transform the constrained optimization to a simpler curve fitting problem that can be formulated analytically. This allows the use of efficient gradient type optimizations, instead of the pattern search optimization that is otherwise required. Examples for optimizing the dimensions of a five-bar planar mechanism demonstrate close correlation of the approximate with the exact solutions, and an order of magnitude better computational efficiency than the previously developed unconstrained optimization methods.

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Division Plane Establishment and Cytokinesis

Annual Review of Plant Biology ◽

10.1146/annurev-arplant-050718-100444 ◽

2019 ◽

Vol 70 (1) ◽

pp. 239-267 ◽

Cited By ~ 17

Author(s):

Pantelis Livanos ◽

Sabine Müller

Keyword(s):

Secretory Pathway ◽

Preprophase Band ◽

Cell Plate ◽

Division Plane ◽

Spatial Reference ◽

Division Site ◽

Eukaryotic Proteins ◽

Plate Formation ◽

Membrane Compartment ◽

Cytoplasmic Content

Plant cells divide their cytoplasmic content by forming a new membrane compartment, the cell plate, via a rerouting of the secretory pathway toward the division plane aided by a dynamic cytoskeletal apparatus known as the phragmoplast. The phragmoplast expands centrifugally and directs the cell plate to the preselected division site at the plasma membrane to fuse with the parental wall. The division site is transiently decorated by the cytoskeletal preprophase band in preprophase and prophase, whereas a number of proteins discovered over the last decade reside continuously at the division site and provide a lasting spatial reference for phragmoplast guidance. Recent studies of membrane fusion at the cell plate have revealed the contribution of functionally conserved eukaryotic proteins to distinct stages of cell plate biogenesis and emphasize the coupling of cell plate formation with phragmoplast expansion. Together with novel findings concerning preprophase band function and the setup of the division site, cytokinesis and its spatial control remain an open-ended field with outstanding and challenging questions to resolve.

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Cytokinesis in tobacco BY-2 and root tip cells: a new model of cell plate formation in higher plants.

The Journal of Cell Biology ◽

10.1083/jcb.130.6.1345 ◽

1995 ◽

Vol 130 (6) ◽

pp. 1345-1357 ◽

Cited By ~ 303

Author(s):

A L Samuels ◽

T H Giddings ◽

L A Staehelin

Keyword(s):

Higher Plants ◽

Membrane Surface ◽

Cell Plate ◽

Root Tip ◽

Cellulose Synthesis ◽

Parent Cell ◽

Cell Periphery ◽

New Model ◽

Cell Plate Formation ◽

Plate Formation

Cell plate formation in tobacco root tips and synchronized dividing suspension cultured tobacco BY-2 cells was examined using cryofixation and immunocytochemical methods. Due to the much improved preservation of the cells, many new structural intermediates have been resolved, which has led to a new model of cell plate formation in higher plants. Our electron micrographs demonstrate that cell plate formation consists of the following stages: (1) the arrival of Golgi-derived vesicles in the equatorial plane, (2) the formation of thin (20 +/- 6 nm) tubes that grow out of individual vesicles and fuse with others giving rise to a continuous, interwoven, tubulo-vesicular network, (3) the consolidation of the tubulo-vesicular network into an interwoven smooth tubular network rich in callose and then into a fenestrated plate-like structure, (4) the formation of hundreds of finger-like projections at the margins of the cell plate that fuse with the parent cell membrane, and (5) cell plate maturation that includes closing of the plate fenestrae and cellulose synthesis. Although this is a temporal chain of events, a developing cell plate may be simultaneously involved in all of these stages because cell plate formation starts in the cell center and then progresses centrifugally towards the cell periphery. The "leading edge" of the expanding cell plate is associated with the phragmoplast microtubule domain that becomes concentrically displaced during this process. Thus, cell plate formation can be summarized into two phases: first the formation of a membrane network in association with the phragmoplast microtubule domain; second, cell wall assembly within this network after displacement of the microtubules. The phragmoplast microtubules end in a filamentous matrix that encompasses the delicate tubulo-vesicular networks but not the tubular networks and fenestrated plates. Clathrin-coated buds/vesicles and multivesicular bodies are also typical features of the network stages of cell plate formation, suggesting that excess membrane material may be recycled in a selective manner. Immunolabeling data indicate that callose is the predominant lumenal component of forming cell plates and that it forms a coat-like structure on the membrane surface. We postulate that callose both helps to mechanically stabilize the early delicate membrane networks of forming cell plates, and to create a spreading force that widens the tubules and converts them into plate-like structures. Cellulose is first detected in the late smooth tubular network stage and its appearance seems to coincide with the flattening and stiffening of the cell plate.

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Phragmoplastin dynamics: multiple forms, microtubule association and their roles in cell plate formation in plants

Plant Molecular Biology ◽

10.1023/b:plan.0000006936.50532.3a ◽

2003 ◽

Vol 53 (3) ◽

pp. 297-312 ◽

Cited By ~ 37

Author(s):

Zonglie Hong ◽

C. Jane Geisler-Lee ◽

Zhongming Zhang ◽

Desh Pal S. Verma

Keyword(s):

Cell Plate ◽

Multiple Forms ◽

Cell Plate Formation ◽

Plate Formation

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Einfluß von Pseudococcus maritimus Ehrh. auf die Zellteilung

Zeitschrift für Naturforschung B ◽

10.1515/znb-1963-0616 ◽

1963 ◽

Vol 18 (6) ◽

pp. 499-500 ◽

Cited By ~ 2

Author(s):

Peter Pfitzer

Keyword(s):

Host Plants ◽

Embryo Sac ◽

Cell Plate ◽

Multinucleated Cells ◽

Cell Plate Formation ◽

Plate Formation ◽

Dividing Cells ◽

Mealy Bug ◽

Pseudococcus Maritimus ◽

Female Flowers

The mealy-bug Pseudococcus maritimus Ehrh. suppresses as specific disturbance cell plate formation in dividing cells of female flowers without interfering with the division of the nuclei. Host plants were three different species of the aroid Aglaonema. The result are multinucleated cells whose differentiation in cells of pistil, ovary, and embryo-sac is practically undisturbed.

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A cometary mechanism for the formation of tektites

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1963.0065 ◽

1963 ◽

Vol 272 (1351) ◽

pp. 467-480 ◽

Cited By ~ 1

Keyword(s):

Small Eccentricity ◽

The Earth ◽

Short Period ◽

Cometary Material ◽

General Order ◽

Order Of Magnitude

Passage of the Earth through a comet must occur on average every million years approximately and last for a time of a few hours. A proportion of short-period comets will have had sufficiently small eccentricity (less than about 0.6) for accretion of cometary material to occur during such passages and produce a narrow jet of material falling vertically down-wards through the atmosphere. The orbits of these comets are such that the jet would be most likely to fall within lower latitudes, as is found for tektite fields. The temperature within the accretion-stream would be sufficiently great to vaporize most materials, and the tektites are regarded as forming from the most refractory substances within the stream, so that they are not characteristic of cometary compositions. The speeds of entry into the atmosphere are high enough for ablation to occur, and the dimensions of the resulting fields and their total masses agree in general order of magnitude with those estimated for actual fields.

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