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Dive into the research topics where Nancy G. Dengler is active.

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Featured researches published by Nancy G. Dengler.


The Plant Cell | 1997

Leaf Vascular Pattern Formation.

Timothy Nelson; Nancy G. Dengler

The pattern and ontogeny of leaf venation appear to guide or limit many aspects of leaf cell differentiation and function. Photosynthetic, supportive, stomatal, and other specialized cell types differentiate in positions showing a spatial relationship to the vascular system. These spatial relationships are of obvious importance to leaf function, which relies on venation for the servicing of cells engaged in photosynthesis, gas exchange, and other leaf processes. Although the need for coordinated organization of cell types around the vascular system is clear, the means by which this is achieved during development is not well understood. In the few systems in which it has been possible to follow the ontogeny of the venation along with the differentiation and function of surrounding cell types (e.g., in C4 grasses), observations suggest that the developing vascular system may have a role in providing positional landmarks that guide the differentiation of other cell types. Another possible explanation is that an underlying pattern guides the differentiation of both venation and surrounding cells. Whether the process of vascularization creates or reveals a pattern, studies to date are largely descriptive, and little is understood of the underlying mechanisms. These mechanisms must be highly regulated, as evidenced by the successful use of species-specific leaf vascular pattern as a taxonomic characteristic (e.g., Klucking, 1992) and by the predictable effect of certain mutations. In this review, we summarize the vascular patterns and their ontogenies in dicots and monocots, referring extensively but not exclusively to Arabidopsis and maize as examples. We also discuss a variety of models that seek to explain vascular pattern formation, and we provide a summary of molecular and genetic investigations of the process.


The Plant Cell | 1994

fusca3: A Heterochronic Mutation Affecting Late Embryo Development in Arabidopsis.

Kallie Keith; Marlene M. Kraml; Nancy G. Dengler; Peter McCourt

Molecular studies of late embryogenesis and seed development have emphasized differential gene expression as a means of identifying discrete stages of embryogenesis. Little has been done to identify factors that regulate the length of a given developmental stage or the degree of overlap between adjacent developmental programs. We designed a genetic screen to identify mutations that disrupt late embryo development in Arabidopsis without loss of hormonal responses. One such mutation, fusca3 (fus3), alters late embryo functions, such as the establishment of dormancy and desiccation tolerance, and reduces storage protein levels. fus3 cotyledons bear trichomes, and their ultrastructure is similar to that of leaf primordia. Immature fus3 embryos enter germinative development, and the shoot apical meristems develop leaf primordia before seed desiccation begins. The cotyledons resemble leaf primordia, yet retain some cotyledon characteristics; thus, cotyledon- and leaf-specific functions are expressed simultaneously. Together, these observations are consistent with a heterochronic interpretation of the fus3 mutation.


The Plant Cell | 2004

Programmed Cell Death Remodels Lace Plant Leaf Shape during Development

Arunika H. L. A. N. Gunawardena; John S. Greenwood; Nancy G. Dengler

Programmed cell death (PCD) functions in the developmental remodeling of leaf shape in higher plants, a process analogous to digit formation in the vertebrate limb. In this study, we provide a cytological characterization of the time course of events as PCD remodels young expanding leaves of the lace plant. Tonoplast rupture is the first PCD event in this system, indicated by alterations in cytoplasmic streaming, loss of anthocyanin color, and ultrastructural appearance. Nuclei become terminal deoxynucleotidyl transferase–mediated dUTP nick end labeling positive soon afterward but do not become morphologically altered until late stages of PCD. Genomic DNA is fragmented, but not into internucleosomal units. Other cytoplasmic changes, such as shrinkage and degradation of organelles, occur later. This form of PCD resembles tracheary element differentiation in cytological execution but requires unique developmental regulation so that discrete panels of tissue located equidistantly between veins undergo PCD while surrounding cells do not.


Current Opinion in Plant Biology | 2001

Vascular patterning and leaf shape

Nancy G. Dengler; Julie Kang

Morphogenesis of leaf shape and formation of the major elements of leaf vasculature are temporally coordinated during leaf development. Current analyses of mutant phenotypes provide strong support for the role of auxin signaling in vascular pattern formation and indicate that leaf shape and vasculature are developmentally coupled. Two other mechanisms that may contribute to the regulation of these processes are a diffusion-reaction system and long-distance signaling of informational macromolecules.


American Journal of Botany | 2007

Diversity of Kranz anatomy and biochemistry in C4 eudicots.

Riyadh Muhaidat; Rowan F. Sage; Nancy G. Dengler

C(4) photosynthesis and Kranz anatomy occur in 16 eudicot families, a striking example of convergent evolution. Biochemical subtyping for 13 previously undiagnosed C(4) eudicot species indicated that 10 were NADP-malic enzyme (ME) and three were NAD-ME. A total of 33 C(4) species, encompassing four Kranz anatomical types (atriplicoid, kochioid, salsoloid, and suaedioid), and 21 closely related C(3) species were included in a quantitative anatomical study in which we found that, unlike similar studies in grasses and sedges, anatomical type had no predictive value for the biochemical subtype. In a multivariate canonical discriminant analysis, C(4) species were distinguished from C(3) species by the mesophyll to bundle sheath ratio and exposure of the bundle sheath surface to intercellular space. Discrimination between NADP-ME and NAD-ME was not significant, although in a Mantel test grouping by biochemical subtype was significant, while grouping by family was not. This comprehensive survey of C(4) anatomy and biochemistry unequivocally demonstrated that atriplicoid anatomy and NADP-ME biochemistry predominate in many evolutionary lineages. In addition to a main decarboxylating enzyme, high activity of a second decarboxylating enzyme was often observed. Notably, PEP-carboxykinase activity was significant in a number of species, demonstrating that this enzyme could also serve as a secondary pathway for C(4) metabolism in eudicots.


American Journal of Botany | 2005

Phylogeny of Flaveria (Asteraceae) and inference of C4 photosynthesis evolution

Athena D. McKown; Jean-Marc Moncalvo; Nancy G. Dengler

A well-resolved phylogeny of Flaveria is used to infer evolutionary relationships among species, biogeographical distributions, and C(4) photosynthetic evolution. Data on morphology, life history, and DNA sequences (chloroplastic trnL-F, nuclear ITS and ETS) for 21 of 23 known species were collected. Each data set was analyzed separately and in combination using maximum parsimony and Bayesian analyses. The phylogeny of Flaveria is based on the combined analysis of all data. Our phylogenetic evidence indicates that C(3) Flaveria are all basal to intermediate (C(3)-C(4) and C(4)-like) and fully expressed C(4) Flaveria species. Two strongly supported clades (A and B) are present. Using this phylogeny, we evaluate the current systematics of the genus and suggest the removal and reevaluation of certain taxa. We also infer the center of origin and dispersal of Flaveria species. Multiple origins of photosynthetic pathway intermediacy in Flaveria are recognized. C(3)-C(4) intermediacy has evolved twice in the genus and is found to be evolutionarily intermediate in clade A, but not necessarily in clade B. C(4)-like photosynthesis is also derived once in each clade. In addition, fully expressed C(4) photosynthesis may have evolved up to three times within clade A.


International Journal of Plant Sciences | 2004

VEIN PATTERN DEVELOPMENT IN ADULT LEAVES OF ARABIDOPSIS THALIANA

Julie Kang; Nancy G. Dengler

Vein pattern development in the leaves of higher plants requires that a continuous system with hierarchical vein size classes and regular spacing be formed de novo from ground meristem precursors. In this study, we use a molecular marker of procambium identity, AtHB‐8::GUS, to investigate the procambial stage of vein pattern formation in adult rosette leaves of Arabidopsis thaliana and to compare the elaboration of AtHB‐8‐marked vein pattern with that expressed by xylem differentiation. While the well‐studied juvenile leaves of Arabidopsis have a relatively simple brochidodromous vein pattern with the simultaneous appearance of the looped secondary veins, adult leaves have a complex semicraspedodromous vein pattern, and a majority of the straight secondary veins develop progressively. Late‐formed secondary veins either arise in the basal portions of the leaf or are intercalated between earlier‐formed secondary veins. Smaller “connector” veins become enhanced during development to form the subterminal loops of the semicraspedodromous secondary vein pattern. Higher‐order veins, especially freely ending veinlets, are formed throughout leaf expansion, maintaining a stable vein density. These unique features of adult leaf vein pattern are strongly correlated with the presence of marginal serrations and a protracted period of leaf expansion. In early leaf development, AtHB‐8::GUS expression precedes any of the hallmark anatomical features of procambial cells in presumptive procambial strands, defining a “preprocambial” stage. In contrast, AtHB‐8::GUS expression was not detected during the late formation of higher‐order veins, indicating that functionally redundant mechanisms guide the development of leaf vascular pattern.


International Journal of Plant Sciences | 2001

Leaf Morphogenesis in Dicotyledons: Current Issues

Nancy G. Dengler; Hirokazu Tsukaya

The last decade of the twentieth century has witnessed a period of renewed interest, redefinition of questions, and some dramatic advances toward resolving some of the long‐standing issues related to the developmental regulation of leaf morphogenesis. New interest has been sparked by the application of developmental genetics, molecular biology, and mosaic analysis to the study of genetic model species. The integration of knowledge gained from these newer approaches with that derived from more than a century of comparative developmental morphology is crucial for advancing understanding of leaf morphogenesis. This link is particularly important for the interpretation of mutant phenotypes and gene expression patterns. In this brief review article, we provide a general framework for the study of leaf morphogenesis and identify areas where we believe that important issues remain unresolved.


Journal of Plant Growth Regulation | 2001

Regulation of vascular development

Nancy G. Dengler

The regulation of vascular development is one of the major unresolved issues of plant developmental biology. This overview provides a framework for the following four papers by describing key events of vascular development and highlighting recent advances in understanding their regulation. Vascular development includes: (1) formation of the longitudinal pattern of primary vascular strands (2) formation of the radial pattern of xylem and phloem within vascular strands (3) differentiation of specialized cell types from xylem and phloem precursors; and (4) cell proliferation and cell differentiation within the vascular cambium. Integration of information from diverse sub-disciplines, including comparative anatomy of primary vascular patterns, manipulative experiments testing the role of hormones in pattern formation and cell differentiation, analysis of mutual phenotypes, detailed characterization of cellular events, and use of molecular tools to identify and determine gene function, will be essential for further progress in understanding the regulation of these processes.


Planta | 2005

Programmed cell death and leaf morphogenesis in Monstera obliqua (Araceae).

Arunika H. L. A. N. Gunawardena; Kathy Sault; Petra M. Donnelly; John S. Greenwood; Nancy G. Dengler

The unusual perforations in the leaf blades of Monstera obliqua (Araceae) arise through programmed cell death early in leaf development. At each perforation site, a discrete subpopulation of cells undergoes programmed cell death simultaneously, while neighboring protoderm and ground meristem cells are unaffected. Nuclei of cells within the perforation site become terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)-positive, indicating that DNA cleavage is an early event. Gel electrophoresis indicates that DNA cleavage is random and does not result in bands that represent multiples of internucleosomal units. Ultrastructural analysis of cells at the same stage reveals misshapen, densely stained nuclei with condensed chromatin, disrupted vacuoles, and condensed cytoplasm. Cell walls within the perforation site remain intact, although a small disk of dying tissue becomes detached from neighboring healthy tissues as the leaf expands and stretches the minute perforation. Exposed ground meristem cells at the rim of the perforation differentiate as epidermal cells. The cell biology of perforation formation in Monstera resembles that in the aquatic plant Aponogeton madagascariensis (Aponogetonaceae; Gunawardena et al. 2004), but the absence of cell wall degradation and the simultaneous execution of programmed cell death throughout the perforation site reflect the convergent evolution of this distinct mode of leaf morphogenesis in these distantly related plants.

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Athena D. McKown

University of British Columbia

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