Formation and cell lineage patterns of the shoot apex of maize (original) (raw)
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Division and differentiation during normal and liguleless-1 maize leaf development
Development (Cambridge, England), 1990
The maize leaf is composed of a blade and a sheath, which are separated at the ligular region by a ligule and an auricle. Mutants homozygous for the recessive liguleless-1 (lg1) allele exhibit loss of normal ligule and auricle. The cellular events associated with development of these structures in both normal and liguleless plants are investigated with respect to the timing of cell division and differentiation. A new method is used to assess orientation of anticlinal division planes during development and to determine a division index based on recent epidermal cross-wall deposition. A normal leaf follows three stages of development: first is a preligule stage, in which the primordium is undifferentiated and dividing throughout its length. This stage ends when a row of cells in the preligule region divides more rapidly in both transverse and longitudinal anticlinal planes. During the second stage, ligule and auricle form, blade grows more rapidly than sheath, divisions in the blade b...
Phase identity of the maize leaf is determined after leaf initiation
Proceedings of the National Academy of Sciences, 2000
The vegetative development of the maize shoot can be divided into juvenile and adult phases based on the types of leaves produced at different times in shoot development. Models for the regulation of phase change make explicit predictions about when the identity of these types of leaves is determined. To test these models, we examined the timing of leaf type determination in maize. Clones induced in transition leaf primordia demonstrated that the juvenile and adult regions of these leaves do not become clonally distinct until after the primordium is 700 μm in length, implying that these cell fates were undetermined at this stage of leaf development. Adult shoot apices were cultured in vitro to induce rejuvenation. We found that leaf primordia as large as 3 mm in length can be at least partially rejuvenated by this treatment, and the location of rejuvenated tissue is correlated with the maturation pattern of the leaf. The amount and distribution of juvenile tissue in rejuvenated leav...
Early event in maize leaf epidermis formation as revealed by cell lineage studies
Development
The epidermal cells of the juvenile leaves of maize are covered by a wax layer. glossy mutants are known which reduce drastically wax deposition. We have used the somatically unstable glossy-1 mutable 8 allele to study the distribution on the epidermis of spontaneous revertant sectors of wild-type tissues. Sectors tend to start and end at positions that correlate with the location on the epidermis of the long costal cells of ribs. It is concluded that in the protoderm only a few cells have a role and position in the generation of each of the developmental modules located between leaf midrib and margin. The module consists of an epidermal strip of cells bordered by two lateral ribs. The module originates from at least 4 cells, with one cell being the progenitor of the other three. Data are provided describing the mode of longitudinal anticlinal epidermal cell divisions within the module that are responsible for the increase in leaf width. The results suggest the existence of a clonal...
Radial leaves of the maize mutant ragged seedling2 retain dorsiventral anatomy
Developmental Biology, 2005
ragged seedling2 (rgd2) is a novel, recessive mutation affecting lateral organ development in maize. The mutant phenotype of homozygous rgd2-R leaves is variable. Mild leaf phenotypes have a reduced midrib and may be moderately narrow and furcated; severe Rgd2-R À leaves are filamentous or even radial. Despite their radial morphology, severe Rgd2-R À mutant leaves develop distinct adaxial and abaxial anatomical features. Although Rgd2-R À mutants exhibit no reduction in adaxial or abaxial cell types, areas of epidermal cell swapping may occur that are associated with misaligned vascular bundles and outgrowths of ectopic margins. Scanning electron microscopy of young primordia and analyses of leaf developmental-marker gene expression in mutant apices reveal that RGD2 functions during recruitment of leaf founder cells and during expansive growth of leaf primordia. Overall, these phenotypes suggest that development is uncoordinated in Rgd2-R À mutant leaves, so that leaf components and tissues may develop quasi-independently. Models whereby RGD2 is required for developmental signaling during the initiation, anatomical patterning, and lateral expansion of maize leaves are discussed.
Clonal Analysis of Epidermal Patterning during Maize Leaf Development
Developmental Biology, 1999
In plants, specialized epidermal cells are arranged in semiordered patterns. In grasses such as maize, stomata and other specialized cell types differentiate in linear patterns within the leaf epidermis. A variety of mechanisms have been proposed to direct patterns of epidermal cell differentiation. One class of models proposes that patterns of cellular differentiation depend on the lineage relationships among epidermal cells. Another class of models proposes that epidermal patterning depends on positional information rather than lineage relationships. In the dicot epidermis, cell lineage is an important factor in the patterning of stomata, but not trichomes. In this study, the role of cell lineage in the linear patterning of stomata and bulliform cells in the maize leaf epidermis is investigated. Clones of epidermal cells in juvenile leaves were marked by excision of dSpm from gl15-m and in adult leaves by excision of Ds2 from bz2-m. These clones were analyzed in relation to patterns of stomata and bulliform cells, testing specific predictions of clonal origin hypotheses for the patterning of these cell types. We found that the great majority of clones analyzed failed to satisfy these predictions. Our results clearly show that lineage does not account for the linear patterning of stomata and bulliform cells, implying that positional information must direct the differentiation patterns of these cell types in maize.
Morphogenesis and Patterning at the Organ Boundaries in the Higher Plant Shoot Apex
Plant Molecular Biology, 2006
Formation of lateral organ primordia from the shoot apical meristem creates boundaries that separate the primordium from surrounding tissue. Morphological and gene expression studies indicate the presence of a distinct set of cells that define the boundaries in the plant shoot apex. Cells at the boundary usually display reduced growth activity that results in separation of adjacent organs or tissues and this morphological boundary coincides with the border of different cell identities. Such morphogenetic and patterning events and their spatial coordination are controlled by a number of boundary-specific regulatory genes. The boundary may also act as a reference point for the generation of new meristems such as axillary meristems. Many of the genes involved in meristem initiation are expressed in the boundary. This review summarizes the cellular characters of the shoot organ boundary and the roles of regulatory genes that control different aspects of this unique region in plant development.
A mutational approach to the study of seed development in maize
Journal of Experimental Botany, 2007
The maize seed comprises two major compartments, the embryo and the endosperm, both originating from the double fertilization event. The embryogenetic process allows the formation of a well-differentiated embryonic axis, surrounded by a single massive cotyledon, the scutellum. The mature endosperm constitutes the bulk of the seed and comprises specific regions containing reserve proteins, complex carbohydrates, and oils. To gain more insight into molecular events that underlie seed development, three monogenic mutants were characterized, referred to as emp (empty pericarp) on the basis of their extreme endosperm reduction, first recognizable at about 12 d after pollination. Their histological analysis reveals a partial development of the endosperm domains as well as loss of adhesion between pedicel tissues and the basal transfer layer. In the endosperm, programmed cell death (PCD) is delayed. The embryo appears retarded in its growth, but not impaired in its morphogenesis. The mutants can be rescued by culturing immature embryos, even though the seedlings appear retarded in their growth. The analysis of seeds with discordant embryo-endosperm phenotype (mutant embryo, normal endosperm and vice-versa), obtained using B-A translocations, suggests that emp expression in the embryo is necessary, but not sufficient, for proper seed development. In all three mutants the picture emerging is one of a general delay in processes related to growth, as a result of a mutation affecting endosperm development as a primary event.
After a century of morphological descriptions and classical genetics maize embryogenesis has been approached over the past decade mainly by molecular genetics. Using forward genetics the cloning of a dozen mutations causing aberrant embryo development has been accomplished leading to the conclusion that mutants with developmental blocks before the coleoptilar stage are more likely to be affected in basic cellular functions than mutants with later blocks or mutants with viable but altered seedlings, which are more likely to be impaired in regulatory genes. By reverse genetics numerous genes with well defined, temporally and/or spatially restricted expression patterns in the maize embryo have been isolated and functions inferred based on sequence analysis and/or expression patterns. In parallel the phenotypic analysis of wildtype and mutant embryo morphology and cytology has made a step forward by the integration of novel methods such as confocal laser scanning microscopy, in situ hybridisation with
The Regulation of Compound Leaf Development
PLANT PHYSIOLOGY, 2001
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The early phase change gene in maize
The Plant cell, 2002
Recessive mutations of the early phase change (epc) gene in maize affect several aspects of plant development. These mutations were identified initially because of their striking effect on vegetative phase change. In certain genetic backgrounds, epc mutations reduce the duration of the juvenile vegetative phase of development and cause early flowering, but they have little or no effect on the number of adult leaves. Except for a transient delay in leaf production during germination, mutant plants initiate leaves at a normal rate both during and after embryogenesis. Thus, the early flowering phenotype of epc mutations is explained completely by their effect on the expression of the juvenile phase. The observation that epc mutations block the rejuvenation of leaf primordia in excised shoot apices supports the conclusion that epc is required for the expression of juvenile traits. This phenotype suggests that epc functions normally to promote the expression of the juvenile phase of shoo...