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B E Lemmon

Publications and source records attributed to B E Lemmon.

6 recordsLinked to original sources
PubMed2002

Cytoskeletal organization of the micropylar endosperm in Coronopus didymus L. (Brassicaceae).

The micropylar chamber of the mustard Coronopus didymus is a developmental domain distinct from the contiguous central chamber and the more extreme chalazal chamber. Early in syncytial development the micropylar endosperm surrounding the embryo becomes populated with unusual fusiform to multilobed nuclei. These nuclei are sheathed by unique parallel arrays of microtubules that focus at tips of the nuclei and flare to connect with a reticulate network in the common cytoplasm. F-actin does not closely invest the nuclei but instead forms an extensive but separate cytoplasmic reticulum. When the embryo is in the early heart stage, the cytoskeleton of the endosperm undergoes a remarkable transition in preparation for cellularization. Microtubules become reorganized into radial arrays emanating from the nuclei, which themselves become spherical. Radial microtubule systems (RMSs), which replace both the parallel microtubules and the cytoplasmic reticulum, organize the common cytoplasm into evenly spaced nuclear cytoplasmic domains (NCDs). F-actin gradually becomes coaligned with the RMSs. Phragmoplasts are initiated adventitiously at the interfaces of opposing RMSs in the absence of mitosis. Cell plate deposition, which is initiated at multiple sites, results in a network of walls formed more or less simultaneously around the densely packed NCDs. The walls, which are rich in 1-3-beta-glucans, join with one another and with the existing walls of both the central cell and embryo to complete cellularization in the micropylar chamber. In the adjacent central chamber where the syncytium is restricted to a thin peripheral layer by the large central vacuole, basic organization of the syncytium into NCDs is followed by alternating cycles of alveolation and periclinal cell division resulting in cellularization.

Brassicaceae↗
PubMed2001

The cytoskeleton and spatial control of cytokinesis in the plant life cycle.

One of the intriguing aspects of development in plants is the precise control of division plane and subsequent placement of walls resulting in the specific architecture of tissues and organs. The placement of walls can be directed by either of two microtubule cycles. The better known microtubule cycle is associated with control of the future division plane in meristematic growth where new cells become part of tissues. The future daughter domains are determined before the nucleus enters prophase and the future site of cytokinesis is marked by a preprophase band (PPB) of cortical microtubules. The spindle axis is then organized in accordance with the PPB and, following chromosome movement, a phragmoplast is initiated in the interzone and expands to join with parental walls at the site previously occupied by the PPB. The alternative microtubule cycle lacks both the hooplike cortical microtubules of interphase and the PPB. Wall placement is determined by a radial microtubule system that defines a domain of cytoplasm either containing a nucleus or destined to contain a nucleus (the nuclear cytoplasmic domain) and controls wall placement at its perimeter. This more flexible system allows for cytoplasmic polarization and migration of nuclei in coenocytes prior to cellularization. The uncoupling of cytokinesis from karyokinesis is a regular feature of the reproductive phase in plants and results in specific, often unusual, patterns of cells which reflect the position of nuclei at the time of cellularization (e.g., the arrangement of spores in a tetrad, cells of the male and female gametophytes of angiosperms, and the distinctive cellularization of endosperm). Thus, both microtubule cycles are required for completion of plant life cycles from bryophytes to angiosperms. In angiosperm seed development, the two methods of determining the boundaries of domains where walls will be deposited are operative side by side. Whereas the PPB cycle drives embryo development, the radial-microtubule-system cycle drives the common nuclear type of endosperm development from the syncytial stage through cellularization. However, a switch to the PPB cycle can occur in endosperm, as it does in barley, when peripheral cells divide to produce a multilayered aleurone. The triggers for the switch between microtubule cycles, which are currently unknown, are key to understanding plant development.

Arabidopsis↗
PubMed2000

The cytoskeleton and polarization during pollen development in Carex blanda (Cyperaceae).

Patterns of cytoskeletal organization during distinct polarizations that characterize pollen development in the sedge Carex blanda (Cyperaceae) were studied by correlated methods of immunohistochemistry and confocal and transmission electron microscopy. As is typical of the family Cyperaceae, Carex produces a unique pollen type known as a pseudomonad in which all four microspores of the tetrad are enclosed within the wall of a single pollen grain. Only one member of the tetrad is functional and the other three abort. The pseudomonads are precisely oriented in the locule with the functional microspore in the wide abaxial portion of the wedge-shaped cytoplasm adjacent to the tapetum, and the degenerative microspores are packed tightly in the pointed adaxial portion. A unique sequence of post-meiotic developmental events reflects both intracellular and intercellular polarity. Development includes: (1) random placement of tetrad nuclei in the coenocytic sporocyte after meiosis, (2) interrupted cytokinesis resulting in a tetrad of nuclei that migrates as a unit into the narrow adaxial tip, (3) completion of unequal cytokinesis and centering of the functional nucleus in the wide abaxial portion of the microsporocyte via a radial array of microtubules and microfilaments, (4) unequal mitosis resulting in a small generative cell at the proximal surface of the functional microspore (adjacent to the abortive microspores), and (5) recentering of the vegetative nucleus in the abaxial cytoplasm via a radial cytoskeletal array.

Journal Article↗
PubMed1998

Nucellain, a barley homolog of the dicot vacuolar-processing protease, is localized in nucellar cell walls.

The nucellus is a complex maternal grain tissue that embeds and feeds the developing cereal endosperm and embryo. Differential screening of a barley (Hordeum vulgare) cDNA library from 5-d-old ovaries resulted in the isolation of two cDNA clones encoding nucellus-specific homologs of the vacuolar-processing enzyme of castor bean (Ricinus communis). Based on the sequence of these barley clones, which are called nucellains, a homolog from developing corn (Zea mays) grains was also identified. In dicots the vacuolar-processing enzyme is believed to be involved in the processing of vacuolar storage proteins. RNA-blot and in situ-hybridization analyses detected nucellain transcripts in autolysing nucellus parenchyma cells, in the nucellar projection, and in the nucellar epidermis. No nucellain transcripts were detected in the highly vacuolate endosperm or in the other maternal tissues of developing grains such as the testa or the pericarp. Using an antibody raised against castor bean vacuolar-processing protease, a single polypeptide was recognized in protein extracts from barley grains. Immunogold-labeling experiments with this antibody localized the nucellain epitope not in the vacuoles, but in the cell walls of all nucellar cell types. We propose that nucellain plays a role in processing and/or turnover of cell wall proteins in developing cereal grains.

Amino Acid Sequence↗
PubMed1997

Cell wall (1-->3)- and (1-->3, 1-->4)-beta-glucans during early grain development in rice (Oryza sativa L.).

Immunogold labeling was used to study the distribution of (1-->3)-beta-glucans and (1-->3, 1-->4)-beta-glucans in the rice grain during cellularization of the endosperm. At approximately 3-5 d after pollination the syncytial endosperm is converted into a cellular tissue by three developmentally distinct types of wall. The initial free-growing anticlinal walls, which compartmentalize the syncytium into open-ended alveoli, are formed in the absence of mitosis and phragmoplasts. This stage is followed by unidirectional (centripetal) growth of the anticlinal walls mediated by adventitious phragmoplasts that form between adjacent interphase nuclei. Finally, the periclinal walls that divide the alveoli are formed in association with centripetally expanding interzonal phragmoplasts following karyokinesis. The second and third types of wall are formed alternately until the endosperm is cellular throughout. All three types of wall that cellularize the endosperm contain (1-->3)-beta-glucans but not (1-->3, 1-->4)-beta-glucans, whereas cell walls in the surrounding maternal tissues contain considerable amounts of (1-->3, 1-->4)-beta-glucans with (1-->3)-beta-glucans present only around plasmodesmata. The callosic endosperm walls remain thin and cell plate-like throughout the cellularization process, appearing to exhibit a prolonged juvenile state.

Cell Wall↗