Browsing by Author "Classen-Bockhoff, Regine"

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    Live imaging of developmental processes in a living meristem of Davidia involucrata (Nyssaceae)
    (2014) Jerominek, Markus; Bull-Herenu, Kester; Arndt, Melanie; Classen-Bockhoff, Regine
    Morphogenesis in plants is usually reconstructed by scanning electron microscopy and histology of meristematic structures. These techniques are destructive and require many samples to obtain a consecutive series of states. Unfortunately, using this methodology the absolute timing of growth and complete relative initiation of organs remain obscure. To overcome this limitation, an in vivo observational method based on Epi-Illumination Light Microscopy (ELM) was developed and tested with a male inflorescence meristem (floral unit) of the handkerchief tree Davidia involucrata Baill. (Nyssaceae). We asked whether the most basal flowers of this floral unit arise in a basipetal sequence or, alternatively, are delayed in their development. The growing meristem was observed for 30 days, the longest live observation of a meristem achieved to date. The sequence of primordium initiation indicates a later initiation of the most basal flowers and not earlier or simultaneously as SEM images could suggest. D. involucrata exemplarily shows that live-ELM gives new insights into developmental processes of plants. In addition to morphogenetic questions such as the transition from vegetative to reproductive meristems or the absolute timing of ontogenetic processes, this method may also help to quantify cellular growth processes in the context of molecular physiology and developmental genetics studies.
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    The role of heterochrony in Schizanthus flower evolution- a quantitative analysis
    (2021) Chinga, Javiera; Perez, Maria Fernanda; Classen-Bockhoff, Regine
    Changes in the timing of development within a lineage (heterochrony) have an enormous impact on floral diversification. However, comparative quantitative studies in a broad range of ontogenetic stages are still needed to identify the role of different heterochronic processes shaping diversification patterns. In this study, changes in petal development were compared across species in the genus Schizanthus showing floral diversification mediated by pollinators. In this genus, transitions from bee-to hummingbird-and moth-pollination are associated with lower lip diversification. Variation in size and shape of petals was quantified at key ontogenetic stages by using a traditional and a geometric morphometric approach. Buds from petal initiation until shortly before anthesis were considered. Lower lip reduction can arise by different combinations of ontogenetic processes such as a delay in organ initiation, a decrease in growth rate, and/or by terminal deletion of the final shape. These processes may interact having an additive effect along ontogeny. Compensatory effects can also occur, as an increase in growth rates can offset the effect of a delay in organ initiation. Heterochronic changes underlying independent reductions of the lower lip varied between lower lip structures: the wing and the keel. While wing reduction was achieved by similar ontogenetic process in both clades, keel reduction was achieved mostly by terminal deletion of the final shape in the moth-pollinated clade and by a decrease in growth rates in the hummingbird-pollinated clade. Therefore, the lower lip structures (keel and wings) originating from the same primordia are governed by different processes indicating that they are discrete developmental units. In conclusion, comparative quantitative studies along a broad range of ontogenetic stages are key to understand how different combinations of onto genetic processes shape morphological variation and promote adaptive evolution.