Abstract
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.
Highlights
One of the most significant technical advances of the last decades in plant sciences is the in vivo observation of developmental processes
A floral units (FU) meristem of D. involucrata was taken from a tree cultivated in the Botanical Garden at the University of Mainz, Germany
MERISTEM DEVELOPMENT The observation began with an undifferentiated meristem (Figure 3A, Video S1)
Summary
One of the most significant technical advances of the last decades in plant sciences is the in vivo observation of developmental processes. While these approaches primarily address gene expression or hormone flux issues (Grandjean et al, 2004; Heisler et al, 2005; Vernoux et al, 2011), traditional imaging techniques such as histology, scanning electron microscopy (SEM), epiillumination light microscopy (ELM) and computer tomography (CT, Staedler et al, 2013) have succeeded in providing clear information regarding morphogenesis at the tissue level These techniques are normally destructive and necessarily imply the observation of many individuals in different developmental states to reconstruct ontogenetic sequences. This approach demands some interpretation, since the same developing structure is not being observed among different samples
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