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Embryologie der Angiospermen
01 Jan 1927-
About: The article was published on 1927-01-01 and is currently open access. It has received 192 citations till now.
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TL;DR: A hypothetical phylogenesis of the tapetum is proposed on the basis of its morphological appearance and of the nutritional relations with meiocytes/spores, and the evolutionary trends of thetapeta tend towards a more and more intimate and increasingly greater contact with the spores/pollen grains.
Abstract: It appears that the tapetum is universally present in land plants, even though it is sometimes difficult to recognize, because it serves mostly as a tissue for meiocyte/spore nutrition. In addition to this main function, the tapetum has other functions, namely the production of the locular fluid, the production and release of callase, the conveying of P.A.S. positive material towards the loculus, the formation of exine precursors, viscin threads and orbicules (= Ubisch bodies), the production of sporophytic proteins and enzymes, and of pollenkitt/tryphine. Not all these functions are present in all land plants:Embryophyta. Two main tapetal types are usually distinguished in theSpermatophyta: the secretory or parietal type and the amoeboid or periplasmodial type; in lower groups, however, other types may be recognized, with greater or lesser differences. A hypothetical phylogenesis of the tapetum is proposed on the basis of its morphological appearance and of the nutritional relations with meiocytes/spores. The evolutionary trends of the tapeta tend towards a more and more intimate and increasingly greater contact with the spores/pollen grains. Three evolutionary trends can be recognized: 1) an intrusion of the tapetal cells between the spores, 2) a loss of tapetal cell walls, and 3) increasing nutrition through direct contact in narrow anthers.
346 citations
TL;DR: Although the suspensor appears to play a critical role in zygotic embryogenesis, it usually fails to develop when somatic embryos are produced in culture and should be viewed as a specialized structure that functions primarily to facilitate continued development of the embryo proper within the seed.
Abstract: The zygote in flowering plants usually divides transversely to form a terminal cell, which gives rise to the embryo proper, and a vacuolated basal cell, which often divides rapidly to form a structure known as the suspensor. Angiosperm suspensors vary widely in size and morphology from a single cell to a massive column of several hundred cells (Maheshwari, 1950; Wardlaw, 1955; Lersten, 1983). In most cases, the suspensor functions early in embryogenesis and then degenerates during later stages of development and is not present in the mature seed. Classically, the suspensor was thought to play a passive role in embryo development by holding the embryo proper in a fixed position within the seed (Maheshwari, 1950). It now appears from extensive structural, biochemical, and physiological studies with a variety of angiosperms that the suspensor plays an active role early in development by promoting continued growth of the embryo proper. In addition, growth of the suspensor during early stages of development may be inhibited by the embryo proper (Marsden and Meinke, 1985). Analysis of reproductive development in angiosperms must therefore include a consideration of developmental interactions that occur between the embryo proper and suspensor. Although the suspensor appears to play a critical role in zygotic embryogenesis, it usually fails to develop when somatic embryos are produced in culture. The suspensor should therefore be viewed as a specialized structure that functions primarily to facilitate continued development of the embryo proper within the seed. In this review, we present an overview of the structure and function of the angiosperm suspensor and discuss recent attempts to analyze the development of the suspensor through a combination of descriptive, experimental, and genetic approaches. The recent identification of a large collection of Arabidopsis mutants with abnormal suspensors provides a unique opportunity to examine the underlying genetic factors that influence suspensor development.
274 citations
TL;DR: A new interpretation of the significance of some major features of vascular plant reproductive biology is put forward, which is that the integuments and endosperm allow the mother to retain control of how her investment is allocated, while deferring the investment until offspring with genotypes different from her own have been created.
Abstract: Here we put forward a new interpretation of the significance of some major features of vascular plant reproductive biology. These features are the integuments of maternal tissue surrounding the offspring, which distinguish seed plants from vascular cryptogams, and the (usually) triploid endosperm produced by double fertilization, which characterizes angiosperms. Maternal integuments and double fertilization are generally regarded as key innovations in plant evolution, and are usually given as the most fundamental characters which distinguish seed plants and angiosperms respectively (Cronquist, 1968; Takhtajan, 1969; Bold, 1973; Foster and Gifford, 1974; Stebbins, 1974; Sporne, 1975; Darlington, 1976). Our interpretation draws together an evolutionary-ecology model on maternal investment, inclusive-fitness calculations from population genetics, and information from comparative plant morphology and embryology. Each of these elements of our interpretation is well-known within the relevant discipline, but the elements have not previously been combined and applied to interpreting plant evolution.1 In this paper we first summarize how mother plants support their offspring in different groups of vascular plants. We show that this support is committed later, with respect to meiosis and fertilization, in more advanced groups of plants. Second, we describe available interpretations, to which our interpretation is an alternative, of the integuments and of double fertilization. Deficiencies of the available interpretations are pointed out, and the points to be explained by our interpretation are defined more exactly. Third, we argue that the advantage achieved by deferring investment in more advanced groups is that mothers can cause a limited total investment to be directed selectively to better offspring genotypes. Fourth, we show that the pattern of investment allocation which maximizes inclusive fitness for the mother is not the same as that which maximizes inclusive fitness for any one offspring. Fifth, we put forward our interpretation, which briefly is that the integuments and endosperm allow the mother to retain control of how her investment is allocated, while deferring the investment until offspring with genotypes different from her own (and therefore with potentially conflicting interests) have been created. Finally, we consider some relatively minor features of comparative plant reproductive biology, which are relevant to assessing our interpretation and other published interpretations.
178 citations
01 Jan 1984
TL;DR: After more than 30 years of research on the nuclear cytology of differentiated tissues, it is now clear that the “supernumerary chromonemal reproduction” at interphase, better called “chromosome endoreduplication” (Levan and Hauschka 1953), is the commonest and most widespread process of cell polyploidization in both plants and animals.
Abstract: In the older literature on angiosperm morphology many examples of very large cells with giant or “hypertrophied” nuclei within differentiated tissues, including reproductive tissues, have been reported, and the connection between nuclear size and trophic activity of the cell has been stressed (references in Schnarf 1929, Tischler 1944, Maheshwari 1950). Goldstein (1928) even attempted to establish a correlation between nuclear form and functional activities of normal and pathological cells. In the absence of adequate knowledge of the mechanisms responsible for the multiplication of the genome, the large size and the variable form (irregular, crenate, lobate, constricted, furrowed, etc.) of nuclei were generally assumed to result from fusion of nuclei and/or amitosis. The significance of restitutional mitosis as a mechanism of doubling the chromosome number was not realized, and was generally regarded as a pathological process. The situation began to change in the late 1930’s—early 1940’s following the discovery of endomitosis in Homoptera, e.g., the pondskaters of the genus Gerris (Geitler 1939), and the proposition that the tetraploid mitoses “with paired chromosomes” (now called “diplochromosomes”) in poly somatic root tips of Spinacia oleracea are due to a double chromosome reproduction at interphase (Berger 1941). After more than 30 years of research on the nuclear cytology of differentiated tissues, it is now clear that the “supernumerary chromonemal reproduction” at interphase (Lorz 1947), better called “chromosome endoreduplication” (Levan and Hauschka 1953), is the commonest and most widespread process of cell polyploidization in both plants and animals (Brodsky and Uryvaeva 1977, D’Amato 1977 a, Nagl 1978).
178 citations
152 citations