The organization of the shoot apex

Wardlaw, C. W.

doi:10.1007/978-3-642-50088-6_29

Cited by 31 publications

(21 citation statements)

References 198 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, in Ephedra and Gnetum the tunica is only one cell thick (Gifford 1943, Johnson 1950, whereas in angiosperms it consists of two layers. This twolayered structure has been confirmed in several angiosperm taxa in the present data set (Nymphaeaceae, Illicium, Schisandraceae, Chloranthaceae, Winteraceae: Gifford 1950, Ramji 1961, Wardlaw 1965). There are angiosperms with one tunica layer, but these belong to groups that are derived in current phylogenies, such as Cactaceae and asterids (Gifford 1954).…”

Section: Methodssupporting

confidence: 84%

Perspective: The Origin of Flowering Plants and Their Reproductive Biology?a Tale of Two Phylogenies

Friedman¹,

Floyd²

2001

Evolution

View full text Add to dashboard Cite

. Recently, two areas of plant phylogeny have developed in ways that could not have been anticipated, even a few years ago. Among extant seed plants, new phylogenetic hypotheses suggest that Gnetales, a group of nonflowering seed plants widely hypothesized to be the closest extant relatives of angiosperms, may be less closely related to angiosperms than was believed. In addition, recent phylogenetic analyses of angiosperms have, for the first time, clearly identified the earliest lineages of flowering plants: Amborella, Nymphaeales, and a clade that includes Illiciales/Trimeniaceae/Austrobaileyaceae. Together, the new seed plant and angiosperm phylogenetic hypotheses have major implications for interpretation of homology and character evolution associated with the origin and early history of flowering plants. As an example of the complex and often unpredictable interplay of phylogenetic and comparative biology, we analyze the evolution of double fertilization, a process that forms a diploid embryo and a triploid endosperm, the embryo‐nourishing tissue unique to flowering plants. We demonstrate how the new phylogenetic hypotheses for seed plants and angiosperms can significantly alter previous interpretations of evolutionary homology and firmly entrenched assumptions about what is synapomorphic of flowering plants. In the case of endosperm, a solution to the century‐old question of its potential homology with an embryo or a female gametophyte (the haploid egg‐producing generation within the life cycle of a seed plant) remains complex and elusive. Too little is known of the comparative reproductive biology of extant nonflowering seed plants (Gnetales, conifers, cycads, and Ginkgo) to analyze definitively the potential homology of endosperm with antecedent structures. Remarkably, the new angiosperm phylogenies reveal that a second fertilization event to yield a biparental endosperm, long assumed to be an important synapomorphy of flowering plants, cannot be conclusively resolved as ancestral for flowering plants. Although substantive progress has been made in the analysis of phylogenetic relationships of seed plants and angiosperms, these efforts have not been matched by comparable levels of activity in comparative biology. The consequence of inadequate comparative biological information in an age of phylogenetic biology is a severe limitation on the potential to reconstruct key evolutionary historical events.

show abstract

Section: Methodssupporting

confidence: 84%

Perspective: The Origin of Flowering Plants and Their Reproductive Biology?a Tale of Two Phylogenies

Friedman¹,

Floyd²

2001

Evolution

View full text Add to dashboard Cite

show abstract

“…rapidly cycling cells. This zonation coincides with the restriction of function to different meristematic regions, with the central zone containing semipermanent initial cells (apical initials) and their recent derivatives (see Wardlaw, 1965;Steeves and Sussex, 1989) and the peripheral zone encompassing the site of organogenesis. Experimental evidence for the existence of semipermanent apical initials comes from analyzing the size, frequency, and persistence of clonal sectors in plants (Stewart and Derman, 1970;Ruth et al, 1985).…”

Section: Introductionmentioning

confidence: 68%

A Mutation in the Arabidopsis TFL1 Gene Affects Inflorescence Meristem Development.

1991

View full text Add to dashboard Cite

We present the initial phenotypic characterization of an Arabidopsis mutation, terminal flower 1-1 (tfll-1 ), that identifies a new genetic locus, TFL1. The tfll-1 mutation causes early flowering and limits the development of the normally indeterminate inflorescence by promoting the formation of a terminal floral meristem. lnflorescence development in mutant plants often terminates with a compound floral structure consisting of the terminal flower and one or two subtending lateral flowers. The distal-most flowers frequently contain chimeric floral organs. Light microscopic examination shows no structural aberrations in the vegetative meristem or in the inflorescence meristem before the formation of floral buttresses. The wild-type appearance of lateral flowers and observations of double mutant combinations of tfll-1 with the floral morphogenesis mutations apetala 7-1 (ap7-1), ap2-1, and agamous (as) suggest that the tfll-1 mutation does not affect normal floral meristems. Secondary flower formation usually associated with the apl-1 mutation is suppressed in the terminal flower, but not in the lateral flowers, of tfll-1 apl-1 double mutants. Our results suggest that tfll-1 perturbs the establishment and maintenance of the inflorescence meristem. The mutation lies on the top arm of chromosome 5 approximately 2.8 centimorgans from the restriction fragment length polymorphism marker 217.

show abstract

“…Regions of the meristem occupied by the radial files appear to resist acropetal bulging, in analogy with the concept of inhibition of initiation of new primordia in the immediate vicinity of existing primordia as proposed in the field theory of phyllotaxis (reviewed in Wardlaw 1965;Schwabe 1984;Steeves and Sussex 1989). The inhibitory field, however, is limited to the narrow strip occupied by the radial files rather than involving the whole area of the meristem facing the full width of the existing primordium.…”

Section: Discussionmentioning

confidence: 91%

“…The regulation of the positioning of emerging leaf primordia at defined locations at the shoot apical meristem (reviewed in Wardlaw 1965;Schwabe 1984;Green 1985;Steeves and Sussex 1989) remains an unresolved problem.-Various factors have been considered to be involVed, such as the size of the apical dome, vertical spacing of existing primordia, or the width of primordia bases. More recent work (Green 1980(Green , 1986Hardham 1982;Jesuthasan and Green 1989;Nelson 1990) has focussed on the possible morphogenetic role of the surface cell layer of the shoot apical meristem.…”

Section: Introductionmentioning

confidence: 99%

Changes in the pattern of cell arrangement at the surface of the shoot apical meristem in Hedera helix L. following gibberellin treatment

Marc

Hackett

1992

Planta

View full text Add to dashboard Cite

The changes in the pattern of cell arrangement and surface topography at the shoot apical meristem of Hedera helix L., which occur during gibberellic acid (GA3)-induced transition from spiral to distichous phyllotaxis, were examined by scanning electron microscopy of rapidly frozen tissue. The technique preserves the original shape of the cells in their turgid state. It reveals distinct sets of radially oriented cell files, about four to eight cells wide, which extend from the central region of the meristem toward leaf primordia on the meristem flanks. In apices with spiral phyllotaxis, a new emerging primordium (0) appears as an acropetal bulge between the radial files adjacent to the third (3) and the second (2) older primordia. The bulging is associated with radial or oblique cell divisions while those located at the meristem flanks and in the radial files are oriented tangentially. As the displacement of existing primordia away from the central region increases following the GA3 treatment, radial and oblique divisions as well as acropetal bulging invade the radial files adjacent to the primordium 2; consequently the angular divergence of the emerging primordium from the youngest existing primordium (1) increases. In apices with distichous phyllotaxis, the earliest bulging appears on both sides of the radial files facing primordium 2, with a slight depression at the files. The radial files therefore correspond to regions of the meristem where acropetal bulging is generally delayed, although this effect apparently diminishes with increasing distance of existing primordia from the meristem center.

show abstract

The organization of the shoot apex

Cited by 31 publications

References 198 publications

Perspective: The Origin of Flowering Plants and Their Reproductive Biology?a Tale of Two Phylogenies

Perspective: The Origin of Flowering Plants and Their Reproductive Biology?a Tale of Two Phylogenies

A Mutation in the Arabidopsis TFL1 Gene Affects Inflorescence Meristem Development.

Changes in the pattern of cell arrangement at the surface of the shoot apical meristem in Hedera helix L. following gibberellin treatment

Contact Info

Product

Resources

About