A critical review of the types of embryo sacs in angiosperms

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Seed evolution: parental conflicts in a multi-generational household

Seeds are multi-generational structures containing a small embryonic plant enclosed in layers of diverse parental origins. The evolution of seeds was a pinnacle in an evolutionary trend towards a progressive retention of embryos and gametes within parental tissue. This strategy, which dates back to the first land plants, allowed an increased protection and nourishing of the developing embryo. Flowering plants took parental control one step further with the evolution of a biparental endosperm that derives from a second parallel fertilization event. The endosperm directly nourishes the developing embryo and allows not only the maternal genes, but also paternal genes, to play an active role during seed development. The appearance of an endosperm set the conditions for the manifestation of conflicts of interest between maternal and paternal genomes over the allocation of resources to the developing embryos. As a consequence, a dynamic balance was established between maternal and paternal gene dosage in the endosperm, and maintaining a correct balance became essential to ensure a correct seed development. This balance was achieved in part by changes in the genetic constitution of the endosperm and through epigenetic mechanisms that allow a differential expression of alleles depending on their parental origin. This review discusses the evolutionary steps that resulted in the appearance of seeds and endosperm, and the epigenetic and genetic mechanisms that allow a harmonious coinhabitance of multiple generations within a single see

Origin of facultative heterochromatin in the endosperm of Gagea lutea (Liliaceae)

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Meiotic and Mitotic Chromosomes of \u3cem\u3eFritillaria atropurpurea\u3c/em\u3e Nutt.

The purpose of this paper is to provide information concerning the number, structure, and behavior of chromosomes in the plant species Fritillaria atropurpurea. The material used for this investigation included both floral buds and root-tips from actively growing naturally occurring plants collected from populations in both Utah and Nevada, and root-tips from seed germinated in the greenhouse. The results obtained include a karyotype analysis of mitotic chromosomes, a discussion of meiosis, a discussion of B-chromosomes, and a series of photographs depicting the stages of mitosis and meiosis in this species. Fritillaria atropurpurea has a diploid chromosome number of 24, plus from zero to two B-chromosomes. Two pair of chromosomes have median centromeres while the other ten pair have sub-terminal to terminal centromeres. Two pair have secondary constrictions and satellites. The length of the chromosomes in colchicine treated material ranges from 12.64 to 19.11 microns, with a width of 2.50 microns. During meiosis, pairing is about 95% complete, and an average of 2.50 chiasmata are formed per bivalent, with no localization of chiasmata observed. There is negligible terminalization between diplotene and anaphase I. Mitosis in this species is regular

Double Fertilization in a Dicotyledon—Caltha palustris1

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Phylogeography and modes of reproduction in diploid and tetraploid halophytes of Limonium species (Plumbaginaceae): evidence for a pattern of geographical parthenogenesis

Background and Aims The genus Limonium (Plumbaginaceae) has long been recognized to have sexual and apomictic (asexual seed formation) modes of reproduction. This study aimed to elucidate phylogeographical patterns and modes of reproduction in diploid and tetraploid Limonium species, namely three putative sexual diploid species with morphological affinities (L. nydeggeri, L. ovalifolium, L. lanceolatum) and three related, probably apomict tetraploid species (L. binervosum, L. dodartii, L. multiflorum). Methods cpDNA diversity and differentiation between natural populations of the species were investigated using two chloroplast sequence regions (trnL intron and trnL–trnF intergenic spacer). Floral heteromorphies, ovule cytoembryological analyses and pollination and crossing tests were performed in representative species of each ploidy group, namely diploid L. ovalifolium and tetraploid L. multiflorum, using plants from greenhouse collections. Key Results and Conclusions Genetic analyses showed that diploid species have a higher haplotype diversity and a higher number of unique (endemic) haplotypes than tetraploid species. Network analysis revealed correlations between cpDNA haplotype distribution and ploidy groups, species groups and geographical origin, and haplotype sharing within and among species with distinct ploidy levels. Reproductive biology analyses showed that diploid L. ovalifolium mainly forms meiotically reduced tetrasporic embryo sacs of Gagea ova, Adoxa and Drusa types. Limonium multiflorum, however, has only unreduced, diplosporic (apomictic) embryo sacs of Rudbeckia type, and autonomous apomictic development seems to occur. Taken together, the findings provide evidence of a pattern of ‘geographical parthenogenesis’ in which quaternary climatic oscillations appear to be involved in the geographical patterns of coastal diploid and tetraploid Limonium speciesinfo:eu-repo/semantics/publishedVersio

Evolutionary Patterns of the Internal Structures of Generative Organs in Angiosperm Plants

Evolutionary patterns of the internal structures of generative organs in angiosperms are considered in light of the idea on their close dependence on the appearance of angiospermy – formation of the ovary closed cavity by carpels– macrosporophylls. A characteristic feature of the sexual process in gymno- and angiosperms is the independency of water for fertilization, unlike all lower plants and pteridophytes. The main direction of the further evolution of the sexual process consisted in the modification for adaptations that ensure the successful fertilization in new conditions. The guidelines and levels of evolution include aromorphosis, allomorphosis, specialization and reduction which are considered to be concrete examples of microstructure of generative organs

Reproductive biology of Centaurea kilaea (Asteraceae, Cardueae) – an endemic species from Türkiye

In this study, the embryology of Centaurea kilaea Boiss., a species endemic to Türkiye, was examined using light microscopy. The anthers of C. kilaea are tetrasporangiate; the anther wall development is dicotyledonous; and the tapetum is amoeboid. The meiotic division of the microspore mother cells is regular, and when the pollen grains are thrown from the anthers, they are three-celled. The ovary of C. kilaea is inferior, bicarpellary, syncarpous, and unilocular, which is characteristic of the Asteraceae family. It carries only a single ovule with basal placentation. The ovule is anatropous, unitegmic, and tenuinucellate. The megaspore mother cell undergoes meiotic division, giving rise to a linear tetrad of megaspores. The chalazal megaspore remains functional, and the other three megaspores degenerate rapidly. The functional megaspore undergoes three mitotic divisions in succession. As a result, a Polygonum-type embryo sac, with eight nuclei and seven cells, is formed. The antipodal cells persist until the first divisions of the zygote. In the mature embryo sac stage, the integument consists of the endothelium, peri-endothelial region, parenchymatous cells, and outer epidermis, from the inside out. Endosperm development is initially free nuclear, becoming cellular in the globular embryo stage. Embryo development is of the asterad type. The mature seed does not contain endosperm, but the endothelium persists

Embryology and fertility of the natural tetraploid Lessingianthus plantaginoides (Asteraceae, Vernonieae): taxonomic implications

Lessingianthus plantaginoides (Vernonieae, Asteraceae) is a small natural tetraploid shrub that inhabits rocky highlands from South America. The population studied inhabits and covers an extensive region of a private reserve with high local biodiversity and animal and plant endemisms. With the purpose of providing insights into the cyto-embryology of this tetraploid species, the aims of this study were: to perform an ontogenetic study of the male and female gametophytes of L. plantaginoides; to carry out detailed meiotic analysis and evaluate the fertility of this species; to document and provide highlights on taxonomic implications of their reproductive aspects. Lessingianthus plantaginoides presented the following male and female gametophyte traits: dicotyledonous type of anther wall development, tetrahedral tetrads, 3-celled mature pollen grains; development of the chalazal megaspore, monosporic embryo sac and Polygonum type of megagametophyte development. The meiotic behavior was regular, the spores were tetrads of equal size and the pollen grains were highly stainable. Lessingianthus plantaginoides is a highly diplodized autotetraploid that reproduces sexually and has high meiotic regularity; which is apparently responsible for its colonization potential. It now seems certain that polyploid speciation plays a significant role in the establishment and diversification of the genus.Lessingianthus plantaginoides (Vernonieae, Asteraceae) é um pequeno arbusto com tetraploidia natural que habita as formações rochosas da América do Sul. A população estudada ocorre e se estende por uma região de uma reserva privada com elevada biodiversidade local e endemismos de animais e vegetais. Com o intuito de fornecer conhecimentos sobre a citologia desta espécie tetraploide, realizamos um estudo ontogenético dos gametófitos masculinos e femininos de L. plantaginoides; fizemos uma análise meiótica detalhada e avaliamos a fertilidade desta espécie; documentamos e demos destaque às implicações taxonômicas dos seus aspectos reprodutivos. Lessingianthus plantaginoides apresentou os seguintes traços dos gametófitos masculinos e femininos: desenvolvimento da parede da antera é do tipo dicotiledôneo, tétrades tetraédricas, grãos de pólen maduros tricelular; desenvolvimento do megásporo calazal, saco embrionário monospórico e desenvolvimento do megagametófito tipo Polygonum. O comportamento meiótico é regular, os esporos são tétrades de igual tamanho e os grãos de pólen são altamente tingíveis. Lessingianthus plantaginoides é um autotetraplóide com alta diplodização que se reproduz sexualmente e tem uma elevada regularidade meiótica; o que é aparentemente responsável pelo seu potencial de colonização. Ao que tudo indica a especiação poliplóide desempenha um papel significativo no estabelecimento e diversificação do gênero.Fil: Pérez, Yanina de Jesús. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; ArgentinaFil: Angulo, Maria Betiana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; ArgentinaFil: Honfi, Ana Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Universidad Nacional de Misiones. Instituto de Biología Subtropical; ArgentinaFil: Dematteis, Massimiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentin