Harnessing the developmental potential of nucellar cells: Barriers and opportunities

Angiosperm nucellar cells can either use or avoid meiosis in vivo, depending on the developmental context. This unique ability contrasts with the conditions required in vitro, either for a reconstituted oocyte to avoid meiosis and produce clones by somatic cell nuclear transfer (SCNT), or for mammalian stem cells to undergo meiosis and produce synthetic sex cells (gametes). Current biotechnological initiatives to harness the potential of nucellar cells are based on the transfer of apomixis genes to sexual crop plants with the aim of producing clones through seeds. The elusive genetic basis of apomixis compels us to examine whether this process involves epigenetic factors. The elegant and versatile developmental platform available in nucellar cells should be explored as a genome-scale science and compared with mammalian stem cell biology for a holistic understanding of developmental programming and reprogramming in eukaryotes

Karyotypic Studies in a Few Species of Barleria L. (Acanthaceae) from South India

Species of Barleria L. numbering about 230 (Airy Shaw 1973) show a wide range of mor phological variations. Some of them are of horticultural interest for their attractive flowers.Nineteen species are known to occur in South India (Gamble 1935).Cytological work in the genus, as in most other members of Acanthaceae, is very little. Though De (1966) and Datta and Maiti (1970) have described karyotypes for a few taxa from North India, those occurring in South India have not received due attention so far. The present work, however, unravels karyotypes in six species distributed in South India and discusses their relationship based on chromosome morphology

Asymmetric cell divisions in flowering plants - One mother, "two-many" daughters

Plant development shows a fascinating range of asymmetric cell divisions. Over the years, however, cellular differentiation has been interpreted mostly in terms of a mother cell dividing mitotically to produce two daughter cells of different fates. This popular view has masked the significance of an entirely different cell fate specification pathway, where the mother cell first becomes a coenocyte and then cellularizes to simultaneously produce more than two specialized daughter cells. The "one mother - two different daughters" pathways rely on spindle-assisted mechanisms, such as translocation of the nucleus/spindle to a specific cellular site and orientation of the spindle, which are coordinated with cell-specific allocation of cell fate determinants and cytokinesis. By contrast, during "coenocyte-cellularization" pathways, the spindle-assisted mechanisms are irrelevant since cell fate specification emerges only after the nuclear divisions are complete, and the number of specialized daughter cells produced depends on the developmental context. The key events, such as the formation of a coenocyte and migration of the nuclei to specific cellular locations, are coordinated with cellularization by unique types of cell wall formation. Both one mother - two different daughters and the coenocyte-cellularization pathways are used by higher plants in precise spatial and time windows during development. In both the pathways, epigenetic regulation of gene expression is crucial not only for cell fate specification but also for its maintenance through cell lineage. In this review, the focus is on the coenocyte-cellularization pathways in the context of our current understanding of the asymmetric cell divisions. Instances where cell differentiation does not involve an asymmetric division are also discussed to provide a comprehensive account of cell differentiation. © Georg Thieme Verlag KG Stuttgart

Female gametophyte development in higher plants - Meiosis and mitosis break the cellular barrier

Meiotic products in higher plants should undergo a determined number of mitotic cycles before differentiating gametes. This creates a unique meiosis-mitosis interface, traverse of which is an absolute requirement for gametophyte development. In the absence of cytokinesis during megasporogenesis - as seen in the bisporic and tetrasporic types - the haploid nuclei produced by meiosis are driven to undergo mitotic cycles within the same cell. Similarly, the last of the mitotic cycles leads to a unique type of cell wall formation resulting in cellularization of the coenocytic female gametophyte, creating a mitosis-cellularization interface. Cell cycle regulation in terms of the molecules that interface with these two key spatio-temporal developmental settings should be of interest to both cell and developmental biologists. High throughput techniques of functional genomics are required for both interpretation of female gametophyte evolution and success of the biotechnological initiatives of transferring apomixis-related genes to crop plants

Ultrastructural Evidence for the Flawless Transmission of a Dicentric Chromosome in Aloe vera. L.

Electronmicroscopic study has revealed a dicentric chromosome in the root tip cells of diploid Aloe vera, hitherto unreported in somatic cells of plants. The morphological aspects are described and the implications of such structural features of the dicentric are addressed in a functional perspective. It is also proposed that the presence of two functional kinetochores need not invariably lead to chromosome instability and loss

A chromatographic study of leaf phenolic compounds in two Citrus interspecific hybrids and their parents

Two interspecific F1 hybrids of Citrus species were examined for inheritance of leaf phenolic compounds. Both the hybrids revealed a reduced number of compounds compared with those of the parents. In addition, the spot pattern of each taxon offered a basis for analysis of inheritance pattern. Due to the production of clones with a consequent reduction in the number of sexual offspring by nucellar embryony in these plants, the unusual pattern of inheritance observed in the hybrids could not be categorized as either a product of disturbed Mendelian ratios or as transgressive segregation affecting only a few individuals in the segregating generations