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Live imaging of developmental processes in a living meristem of Davidia involucrata (Nyssaceae).

Jerominek M, Bull-Hereñu K, Arndt M, Claßen-Bockhoff R - Front Plant Sci (2014)

Bottom Line: The growing meristem was observed for 30 days, the longest live observation of a meristem achieved to date.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.

View Article: PubMed Central - PubMed

Affiliation: Institut für Spezielle Botanik, Johannes Gutenberg-Universität Mainz, Germany.

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.

No MeSH data available.


Related in: MedlinePlus

Development of reproductive meristems. (A) The relative size of flower primordia (filled semicircles) of a reproductive meristem (large dome) is generally used to reconstruct the sequence of initiation (arrow), which either occurs toward the center, i.e., “centripetal” (left sketch), or toward the flanks, i.e., “centrifugal” (right sketch). (B) Different growing rates of simultaneously initiated flower primordia lead to a false interpretation of the initiation sequence (here centrifugal). (C–E), SEM images of a developing FU of Davidia involucrata: (C) Young meristem starting to fractionate flower primordia. (D) Later stage, with many flower primordia initiated. Note that the most basal primordia (red) are smaller. (E) A male FU meristem with stamen initiation in equatorial primorida and delayed development of the most basal flowers (red). All SEM images are in the same scale, bar line = 500 μm. (F) Male inflorescence (FU) of D. involucrata subtended by two conspicuous extrafloral bracts.
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Figure 1: Development of reproductive meristems. (A) The relative size of flower primordia (filled semicircles) of a reproductive meristem (large dome) is generally used to reconstruct the sequence of initiation (arrow), which either occurs toward the center, i.e., “centripetal” (left sketch), or toward the flanks, i.e., “centrifugal” (right sketch). (B) Different growing rates of simultaneously initiated flower primordia lead to a false interpretation of the initiation sequence (here centrifugal). (C–E), SEM images of a developing FU of Davidia involucrata: (C) Young meristem starting to fractionate flower primordia. (D) Later stage, with many flower primordia initiated. Note that the most basal primordia (red) are smaller. (E) A male FU meristem with stamen initiation in equatorial primorida and delayed development of the most basal flowers (red). All SEM images are in the same scale, bar line = 500 μm. (F) Male inflorescence (FU) of D. involucrata subtended by two conspicuous extrafloral bracts.

Mentions: 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), epi-illumination light microscopy (ELM) and computer tomography (CT, Staedler et al., 2013) have succeeded in providing clear information regarding morphogenesis at the tissue level. Unfortunately, these techniques are normally destructive and necessarily imply the observation of many individuals in different developmental states to reconstruct ontogenetic sequences. Thus, this approach demands some interpretation, since the same developing structure is not being observed among different samples. Particularly, this can become a complex issue when reconstructing the development of numerically variable structures, e.g., condensed inflorescences known as “floral units” (Claßen-Bockhoff and Bull-Hereñu, 2013). In floral units (FU), flower primordia usually fractionate in either a centripetal [e.g., umbellets in Apiaceae, (Bull-Hereñu and Claßen-Bockhoff, 2010)] or centrifugal sequence [e.g., cyathia in Euphorbia, (Prenner and Rudall, 2007)] (Figure 1A). If primordia appear almost simultaneously the sequence is interpreted from the arrangement and size of flower primordia, assuming that the smaller ones have been initiated later (Figure 1A). A direct size-age correlation is used because of the a priori assumption that all flower primordia share similar growth rates. However, simultaneous initiation of primordia but a slower growth rate in the basal primordia would create a false impression of centrifugal initiation (Figure 1B).


Live imaging of developmental processes in a living meristem of Davidia involucrata (Nyssaceae).

Jerominek M, Bull-Hereñu K, Arndt M, Claßen-Bockhoff R - Front Plant Sci (2014)

Development of reproductive meristems. (A) The relative size of flower primordia (filled semicircles) of a reproductive meristem (large dome) is generally used to reconstruct the sequence of initiation (arrow), which either occurs toward the center, i.e., “centripetal” (left sketch), or toward the flanks, i.e., “centrifugal” (right sketch). (B) Different growing rates of simultaneously initiated flower primordia lead to a false interpretation of the initiation sequence (here centrifugal). (C–E), SEM images of a developing FU of Davidia involucrata: (C) Young meristem starting to fractionate flower primordia. (D) Later stage, with many flower primordia initiated. Note that the most basal primordia (red) are smaller. (E) A male FU meristem with stamen initiation in equatorial primorida and delayed development of the most basal flowers (red). All SEM images are in the same scale, bar line = 500 μm. (F) Male inflorescence (FU) of D. involucrata subtended by two conspicuous extrafloral bracts.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
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Figure 1: Development of reproductive meristems. (A) The relative size of flower primordia (filled semicircles) of a reproductive meristem (large dome) is generally used to reconstruct the sequence of initiation (arrow), which either occurs toward the center, i.e., “centripetal” (left sketch), or toward the flanks, i.e., “centrifugal” (right sketch). (B) Different growing rates of simultaneously initiated flower primordia lead to a false interpretation of the initiation sequence (here centrifugal). (C–E), SEM images of a developing FU of Davidia involucrata: (C) Young meristem starting to fractionate flower primordia. (D) Later stage, with many flower primordia initiated. Note that the most basal primordia (red) are smaller. (E) A male FU meristem with stamen initiation in equatorial primorida and delayed development of the most basal flowers (red). All SEM images are in the same scale, bar line = 500 μm. (F) Male inflorescence (FU) of D. involucrata subtended by two conspicuous extrafloral bracts.
Mentions: 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), epi-illumination light microscopy (ELM) and computer tomography (CT, Staedler et al., 2013) have succeeded in providing clear information regarding morphogenesis at the tissue level. Unfortunately, these techniques are normally destructive and necessarily imply the observation of many individuals in different developmental states to reconstruct ontogenetic sequences. Thus, this approach demands some interpretation, since the same developing structure is not being observed among different samples. Particularly, this can become a complex issue when reconstructing the development of numerically variable structures, e.g., condensed inflorescences known as “floral units” (Claßen-Bockhoff and Bull-Hereñu, 2013). In floral units (FU), flower primordia usually fractionate in either a centripetal [e.g., umbellets in Apiaceae, (Bull-Hereñu and Claßen-Bockhoff, 2010)] or centrifugal sequence [e.g., cyathia in Euphorbia, (Prenner and Rudall, 2007)] (Figure 1A). If primordia appear almost simultaneously the sequence is interpreted from the arrangement and size of flower primordia, assuming that the smaller ones have been initiated later (Figure 1A). A direct size-age correlation is used because of the a priori assumption that all flower primordia share similar growth rates. However, simultaneous initiation of primordia but a slower growth rate in the basal primordia would create a false impression of centrifugal initiation (Figure 1B).

Bottom Line: The growing meristem was observed for 30 days, the longest live observation of a meristem achieved to date.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.

View Article: PubMed Central - PubMed

Affiliation: Institut für Spezielle Botanik, Johannes Gutenberg-Universität Mainz, Germany.

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.

No MeSH data available.


Related in: MedlinePlus