Morphogenetic Differences Research Articles

Morphogenetic adaptation to defoliation and soil fertility in perennial ryegrass (Lolium perenne)

Morphogenetic adaptation, plasticity, and mortality of four perennial ryegrass populations, representing different selection histories, were compared in response to soil fertility and to defoliation severity. In a second experiment, morphogenetic adaptation and plasticity in response to defoliation frequency were studied in two divergent sub‐populations. Genetic variability was found between ryegrass populations for leaf appearance and elongation rates, leaf size, and tiller number. All populations exhibited plasticity in response to defoliation severity and soil fertility. There was no genetic variation for plasticity, the morphological response to the environment. Morphogenetic differences between populations remained constant across environments and resulted in differential mortality under the most severe defoliation. Both leaf length and rate of leaf appearance were positively correlated with greater mortality. The ryegrass ideotype for hill country is a compromise between yield and persistence.

Morphological and histological differences in the development of dwarf mutants of sexual and somatic origin in diverse woody taxa

Morphological and histological observations were made on eight dwarf mutants arising either as seedlings from sexual reproduction or from somatic bud mutations (witches'-brooms in the crowns of normal trees). The most predominate morphological trait contributing to the expression of dwarfism in all taxa was the reduction of final internode lengths along the shoot axis. In taxa of sexual origin, with the exception of Prunus, there was a consistent reduction in the number of preformed leaves contained in the winter buds. In addition, in two taxa (Liquidambar and Tsuga) there was an almost complete absence of neoformed leaves and sylleptic branches on current year shoots. Conversely, in mutants of somatic origin there was no apparent reduction in the number of preformed leaves. Genetic dwarfness in this group resulted solely from decreases in final internode length. Significant differences in the cellular basis of dwarfism between mutants of different genetic origins are clearly evident. In dwarf trees arising from sexual reproduction, reduction in final internode length is attributed predominately to inhibition of mitotic activity in developing internodes resulting in highly significant decreases in final cell number, and not cell length. In mutants of somatic origin, the reduction in length of mature internodes results from a decrease in final cell length, rather than a decrease in cell number. Physiological mechanisms associated with the genetic expression of these morphogenetic differences are suggested.

HOM-C/Hox genes and four interacting loci determine the morphogenetic properties of single cells in the nematode male tail.

The copulatory structure of the C. elegans male tail includes a set of nine bilaterally symmetrical pairs of sense organs known as rays. Each ray comprises three cells, which are generated by a stereotyped cell sublineage expressed by 18 epidermal ray precursor cells. A pattern formation mechanism in the epidermis guides the specification of morphogenetic differences between the rays necessary for correct organelle assembly at specific positions within the epidermis. Expression of these ray differences was altered in mutations we described previously, resulting in displaced and fused rays. Here we show that two genes of the C. elegans HOM-C/Hox gene complex play a role in the pattern formation mechanism. Increasing or decreasing the gene dosage of mab-5, an Antennapedia homolog, and egl-5, an Abdominal B homolog, results in displacement and fusion of specific rays. These changes are interpreted as anterior or posterior transformations in ray identities. Mutations in the genes previously described are dominant modifiers of these effects. This suggests that these genes act in the same morphogenetic pathway as mab-5 and egl-5. Several lines of evidence, including cell ablation experiments, argue that the identity of each ray is specified cell-autonomously in the terminal cells of the ray lineages. mab-5 and egl-5, therefore, specify the morphogenetic properties of differentiating cells, without change in cell lineage or apparent cell type. Modifier genes may act upstream of mab-5 and egl-5 to regulate their expression. Alternatively, they may act at the same step in the pathway, as cofactors, or they may be target genes. Target genes could include genes specifying cell recognition and adhesion molecules governing ray organelle assembly.

Effects of retinoic acid on the expression of retinoic acid receptors during zebrafish embryogenesis

The cDNAs encoding the zebrafish homologs of retinoic acid receptor α (zRARα) and γ (zRARγ) were isolated and their expression studied in normal and retinoic acid (RA) treated embryos. Expression boundaries in the central nervous system are clearly different from those observed in the mouse, which can only partly be explained by morphogenetic differences. Treatment of embryos with RA induces ectopic zRARγ expression in anterior brain structures and both zRARα and zRARγ expression in the eyes. Furthermore, striking differences occur in the zRARγ expression pattern in pharyngeal arch mesenchyme. Since the development of all of these structures has been shown to be affected by exogenous RA, our data suggest a role for zRARα and zRARγ in the establishment of the RA phenotype in zebrafish.

Morphogenetic Differences between Fore and Hind Limb Precartilage Mesenchyme: Relation to Mechanisms of Skeletal Pattern Formation

Using a serum-free culture system, we have investigated morphogenetic differences between fore and hind limb precartilage mesenchymal cells derived from stages 21-26 chicken embryos. Across all stages, wing and leg cultures were intrinsically different in the amount and spatial organization of cartilage that they produced. By stage 24, leg cells began to produce a nodular pattern of cartilage while wing cells continued to produce sheets of cartilage. This pattern difference persisted throughout the later stages and was not due to differences in cell survival as judged by DNA content or to the presence of distinctive cell subpopulations in either tissue, as determined by flow cytometry. Chondrogenesis in wing and leg precartilage cell cultures was affected differently by 10% fetal bovine serum, TGF-β1 (1 ng/ml for 5 hr on the day after plating), and retinoic acid (5 ng/ml). In wing cultures, the extent of chondrogenesis was significantly enhanced by serum or by a combination of TGF-β1 and retinoic acid, but the cartilage pattern was not altered with any treatment. In leg cultures, the extent of chondrogenesis was enhanced by TGF-β1 alone, inhibited by retinoic acid alone, and the cartilage pattern was changed from nodular to sheet-like by treatment with TGF-β1. Wing and leg cultures also differed from each other in relative cohesivity and in condensation morphology and organization of fibronectin during the early phase of differentiation. Wing cells produced broad, flat condensations containing diffusely organized fibronectin, whereas leg cells elaborated an extensive network of long fibronectin-rich fibrils connecting very compact, fibronectin-rich condensations. These intrinsic and induced differences in fore and hind limb mesenchyme provide insight into the mechanisms that are common to the formation of all limb skeletal elements and those that distinguish skeletal elements from different limb regions and limb types.

Divisional morphogenesis in Bakuella pampinaria nov. spec, and reevaluation of the classification of the urostylids (ciliophora, hypotrichida)

A new hypotrichous ciliare, Bakuella pampinaria nov. spec, colonizing vineleaf and pear-tree litter, is described. Bakuella pampinaria differs from the other species of the genus by having distinct rows of yellowish cortical granules. Several morphogenetic differences separate Bakuella pampinaria from Bakuella edaphoni and other congeners, especially in that the transverse cirri do not participate in the formation of the oral primordium. The type population of Pseudourostyla cristata was reinvestigated. Two frontoterminal cirri are recognizable in dividing specimens indicating that this genus is valid, i.e. different from Urostyla, which very likely lacks such cirri. The urostyline hypotrichs are recognized as a monophyletic taxon by two apomorphies, viz. the midventral cirri and the partial or complete reorganization of the proter's adorai zone of membranelies during cell division. Phylogeny and evolution within the urostylids are much less clear since character states (apomorphies, plesiomorphies, convergencies) are uncertain and morphogenetic data are still too sparse or inaccurate. This is exemplified on a selected set of genera using Hennig's phylogenetic method.

Genetic and environmental factors in the development of so-called pseudo- and true mesioclusions

Separation of genetic and environmental factors related to the development of so-called pseudo- and true mesioclusions was attempted and the classification, which is in common use in clinical orthodontics, reconsidered. A differential diagnosis of these two types of mesioclusions was made depending on whether or not the mandible slid forward into displacement by incisal guidance. By means of lateral roentgenographic cephalograms obtained from 66 pseudo- and 48 true mesioclusion patients and 52 control subjects, and their respective parents, the craniofacial morphogenetic characteristics of each mesioclusion were determined. A familial tendency to prognathic skeletal profile was noted in cases of both pseudo- and true mesioclusions. Nearly all of the significant morphogenetic differences between the two groups of patients with mesioclusion were related to environmental factors. The terms “pseudo” and “true” are probably misleading expressions for these mesioclusions.

Modes and Mechanisms of Plant Speciation: Introduction

In a 1977 volume of Benchmark papers (Jameson 1977) concerning the genetics of speciation only five of the 27 papers focus on any plant species as the study organism. The remaining 22 papers focus on animal species. The same is true for a recent symposium on mechanisms of speciation (Barigozzi 1982), where most of the contributions concern animal taxa. This symposium was organized with the hope that it would stimulate needed research in modes and mechanisms of plant speciation. While plant systematists direct considerable effort toward discerning similarity, documenting adaptations within species, and conducting cladistic analyses of taxa at various levels, our understanding of speciation events in plants, especially for perennial taxa, is quite limited. Even though flowering plants, especially annual species, offer certain logistical advantages for analyzing processes of speciation (Stebbins 1982), botanists tend to lag behind zoologists in this area of research. Crawford (this symposium) suggests that botanists have been unduly influenced by zoologists in developing ideas about plant speciation. The possibility that fundamental morphogenetic and developmental differences between plants and animals may require different hypotheses for explanations of the mode of origin and evolution of morphological characters in the two kingdoms has important implications for speciation theory (Gottlieb 1984, p. 682), and further mandates a resurgence of basic research in modes and mechanisms of plant speciation. This symposium was sponsored by the American Society of Plant Taxonomists and the Systematics and Genetics Sections of the Botanical Society of America at the meetings of the American Institute of Biological Sciences, Colorado State University, 5-9 August 1984. Contributors were Hampton Carson, Ray C. Jackson, Daniel J. Crawford, Amy Jean Gilmartin, Jerrold I Davis, and Warren H. Wagner, Jr.

Cladotricha and Phylogeny in the Suborder Stichotrichina (Ciliophora, Hypotrichida)*

Synopsis.The cortical anatomy and morphogenesis of Cladotricha koltzowii Gajewskaja and Cladotricha variabilis Rumen from the Great Salt Lake, Utah, are described. When compared with 2 marine hypotrichs, Uroleptoides kihni Wenzel and Stichotricha secunda Kahl, from the east coast of the United States, their structure and development suggest that Cladotricha may have descended from an intermediate species within the line of evolution of the Spirofilidae from primitive Kahliella‐like hypotrichs. It is suggested that the Kahliella‐Cladotricha‐Uroleptoides series is separated at the familial level from both the tubicolous and planktonic spirofilids. Further, the structural and morphogenetic differences between Cladotricha and the holostichid Uroleptus appear to be at a subordinal level. These findings are significant in revising definitions of the Hypotrichida, its suborders, and the Urostylidae.

Studies on the development, life history and taxonomy of the Ectocarpales (Phaeophyta) in southern Australia

The morphology, development and life history of filamentous brown algae, in particular species of the commoner genera Feldmannia, Giffordia and Hecatonema, are described. Morphogenetic differences parallel the well known morphological distinctions between Feldmannia and Giffordia. Two 'species' of Feldmannia, F. globifer and F. simplex, are not distinct but rather exhibit continous variation of a clinal nature. Previous records of Giffordia secunda are shown to apply to Giffordia granulosa. Studies of living and type material of Ectocarpus sordidus indicate that its affinities lie with the genus Giffordia, to which it is transferred. Life histories of the various ectocarpalean taxa show many similarities and, with minor exceptions do not furnish additional useful taxonomic characters. The predominant means of reproduction amongst the Australian Ectocarpales are asexual, sexual processes being apparently of minor signi- ficance. Life history studies of Hecatonema maculans show it to be indistinct from juvenile stages of two members of the Dictyosiphonales, Desmotrichum undulatum and Punctaria latifolia. Five genera and six species are newly recorded for Australia. The genera are Acinetospoua, Hecatonenza, Kuckuckia, Kuetzingiella and Sovocarpus and the species are Acinetospora crinita (Carmichael ex Harvey in J. D. Hooker) Kornmann, Giffordia fuscata (Zanardini) Kornmann in Kuckuck, Giffordia intermedia (Rosenvinge) Lund, Hecatonema maculans (Collins) Sauvageau, Kuckuckia spinosa (Kiitzing) Kuckuck and Sorocarpus micromorus (Bory) Silva.

GENETIC VARIATION IN THE ORIENTATION OF NUCLEAR SPINDLES DURING THE DEVELOPMENT OF ASCI IN NEUROSPORA

The effect of a single mutant gene, peak‐2, in Neurospora crassa is to alter the ascus from one in which the eight spores are linearly arranged to one in which the eight spores are arranged non‐linearly. The same gene transferred to N. tetrasperma determines an ascus similar to that of the mutant N. crassa but in striking contrast to the normal ascus for N. tetrasperma, which includes four heterokaryotic spores, linearly arranged. A comparative cytological study has been made on asci from both species, including material from zygotes that are homozygous normal, heterozygous for peak‐2, and homozygous for peak‐2. The observed morphogenetic differences are closely related to differences in nuclear spindle orientation, which in turn are correlated with the geometry of the cell. The observations are shown to bear on the basis of pseudohomothallism in N. tetrasperma. Speculations on the importance of the cell wall in relation to spindle orientation are presented. Differences of expression of peak‐2 in the different species are discussed.

Morphogenetic Differences Between Nicotiana alata and N. Langsdorffii as Indicated by Their Response to Indoleacetic Acid

An unusual opportunity for the application of the present knowledge of hormones to the investigation of morphogenetic differences between two closely related species is afforded by Nicotiana alata and Nicotiana Langsdorffii. The flowers of the two species are similar, but the difference in the size of the corolla parts suggests a possible interpretation in terms of hereditary response to growth substance. One of the chief differences lies in the constricted part of the corolla-tube (pl. 25, fig. 1). In N. alata its length is at least fifteen to twenty times that of N. Langsdorffii, whereas the whole corolla in the former is only four or five times the length of the latter. The epidermal cells of the tube of N. alata are extremely long; those of N. Langsdorffii, relatively short. The work on several known genetic dwarf races of corn by van Overbeek ('35, '38) indicates that the varietal differences are 'due to genetic differences which regulate production, use, and inactivation of auxin. The experiments on Epilobium hybrids by Schlenker and Mittman, cited by Went and Thimann ('37), suggest this same relationship. If this hypothesis holds true for species of Nicotiana and the differences between them are due to differences in amount of hormone produced, then auxin should prove to be a limiting factor in N. Langsdorffii and its application to the corollas of this species should then cause an increase in size. If differences are due to differences in ability to use growth substance, then auxin should be a limiting factor in N. alata and additional amounts should increase