Roy C. Brown

My research interests are in the developmental morphology of plants. The simple land plants - bryophytes, ferns and fern allies - are the organisms of choice for investigation of several important phenomena. Since the morphology of a mature plant depends on the planes of cell division during development, our understanding of plant growth depends upon elucidation of how plant cells control the plane of cell division. Toward this goal, I am conducting an investigation of the development of the cytokinetic apparatus in both mitotic and meiotic cell division in a variety of organisms. Patterns of microtubules and microfilaments that develop during the cell cycle are studied by techniques of indirect immunofluorescence and transmission electron microscopy. Of particular interest are the few land plants that maintain a single plastid through cell division. In these monoplastidic cells the plastid migration, particularly those migrations that predict the future plane of nuclear division, and studies of cytoplasmic microtubules systems that are elaborated prior to nuclear division are expected to provide new insight into poorly understood cytological phenomena.

Another major research area in our laboratory is the study of the developmental biology of seed endosperm. We are studying endosperm as a model system for investigating the placement and orderly deposition of plant cell walls. Endosperm of the monocotyledons rice, and maize and the dicotyledon Arabidopsis all exhibit the nuclear type of endosperm development in which cellularization of the multinucleate syncytium occurs as a coordinated process involving the cell cycle, cytoskeleton and wall deposition. Information from these studies contribute to knowledge of cardinal processes in plant development and understanding the endosperm, the valuable food storage component of cereal grains.

In addition to these programs, we have a longstanding interest in structural and developmental aspects of plant reproduction, especially of pollen and spores, and plant ultrastructure in general.

A panorama of a mitotic wave showing orderly rows of nuclei in successive stages of mitosis. A sheet of tissue was removed from the developing female gametophyte of Ginkgo biloba and prepared for study of microtubules (green) and nuclei/chromosomes (red) by immunohistochemistry and confocal microscopy. The syncytium exhibits the nuclear cytoplasmic domain (NCD) pattern of division in which radial microtubule systems (RMS) (far right and left in movie) organize the cytoplasm. The RMSs serve several interrelated functions in cytoplasmic organization: 1) they space the NCDs into a hexagonal pattern, 2) they establish a fabric providing tensegrity to the "liquid" endosperm, and 3) they are an integral component of the cell cycle as they undergo disassembly in prophase, are absent in metaphase/anaphase, reassembled in telophase and completely surround nuclei throughout interphase. Transition from interphase to prophase can be seen as gradual enlargement of nuclei and concomitant disassembly of RMS. Perinuclear assembly of the anastral spindle, nuclear envelope breakdown, and transition to metaphase appear to be rapid. The interzonal arrays of anaphase/telophase disappear without organizing a phragmoplast. RMSs reassemble around telophase nuclei and reestablish the network of interacting RMSs of interphase which define NCDs and the cycle repeats. Up to three such "mitotic waves" may occur in the same syncytium. Based on observations of the mitotic waves, we propose that an additional important function of RMSs is the communication of developmental cues from one NCD to another. Even though nuclei are in a common cytoplasm, it is clear that NCDs are the functional units of organization and that developmental cues required for the mitotic wave are transmitted from one to another in an orderly manner. For full text see: Brown, R. C., Lemmon, B. E., and H. Nguyen. The microtubule cycle during successive mitotic waves in the syncytial female gametophyte of ginkgo. J. Plant Res. (In press).

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