Download 3D Visualization of Thylakoid Membrane

The Plant Cell, Vol. 28: 827–828, April 2016, www.plantcell.org ã 2016 American Society of Plant Biologists. All rights reserved.
IN BRIEF
3D Visualization of Thylakoid Membrane Development
Proper biogenesis of the chloroplast is
essential for all photosynthetic plant cells.
As germinating seedlings are exposed to
light, etioplasts in young mesophyll cells
become chloroplasts in the developing
seedling. The chloroplast thylakoids develop from a paracrystalline tubular structure that is transformed when illuminated
into a series of flattened membranes that
become the grana thylakoids. Traditional
transmission electron microscopy (TEM)
shows subcellular fine structure in twodimensional thin slices, but a comprehensive study of chloroplast biogenesis
requires 3D visualization of membrane
transformations.
Electron tomography (ET) creates 3D reconstructions of subcellular objects by taking a series of traditional TEMs collected
at different angles and using computer algorithms to generate detailed views of the
surfaces of structures (Shimoni et al., 2005;
Daum and Kühlbrandt, 2011). Kowalewska
et al. (2016) have used ET and confocal laser
scanning microscopy to follow the development of stacked grana thylakoids as etiolated runner bean (Phaseolus coccineus)
seedlings are exposed to light. They characterize membrane structure during the
first 3 d of illumination (under a 16-h-light/
8-h-dark photoperiod) of dark-adapted
seedlings.
After 8 d of etiolation, etioplasts in darkadapted seedlings showed a regular arrangement of branched membrane tubules.
These tubular units are joined as a paracrystalline network in the prolamellar
body (PLB), much like the cells in a honeycomb (see figure, A and B). As soon as
1 h after illumination, the symmetry of the
PLB was lost as the internal membranes
rearranged (figure, C). The tetrahedral
network was no longer visible and the
margins of the tubules developed flattened stromal slats that would develop
into prothylakoids.
After 2 h of illumination, only a remnant of the PLB was present and memOPEN
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Thylakoid development in three dimensions. As dark-adapted runner bean seedlings are illuminated,
the paracrystalline prolamellar body of the etioplast ([A] and [B]) becomes disorganized ([C] and [D]),
as membranes flatten ([E] and [F]) and are transformed into stacked grana ([G] and [H]). (Reprinted
from Kowalewska et al. [2016].)
branes became organized parallel to
the long axis of the chloroplast (figure,
D). These PLB remnants were continuous, as opposed to the porous membranes seen in prothylakoids (PTs). By
4 h, the PLB was transformed into a parallel arrangement of PTs with local connections, often split dichotomously into
two adjacent branches (figure, E). By
8 h, the first stacked membranes had
appeared (figure, F). The appressed
thylakoids were no longer porous and
membranes were seen to be continuous in stacked regions, with each
stacked membrane connected to a single split PT.
By the beginning of the second day,
small grana stacks were observed, and
both stroma thylakoids and grana thylakoids were evident (figure, G). Each stroma
thylakoid was connected to two adjacent
grana thylakoids at an angle of ;20˚, as
seen by Austin and Staehelin (2011). By
day 3, stroma thylakoids had split dichotomously, connecting with two grana thylakoids, except at the top and bottom of
the grana stack, where the stroma thylakoid connected to only one grana thylakoid (figure, H).
The entire transformation of the paracrystalline tubular membrane network of
the PLB to the organized, stacked grana
thylakoid membranes is shown in a sup-
plemental movie created by the authors
in 2D and 3D (this wonderful video should
not be missed!). Every stage of thylakoid
development is shown in a traditional
TEM view, outlining the membranes to
be visualized in 3D. Then, the 3D structures of the outlined areas are presented
and rotated to show membrane surfaces
from many angles during the membrane
transformations.
The authors also use confocal laser
scanning microscopy to monitor red chlorophyll fluorescence, as it helps to show
the distribution of appressed thylakoids.
And, because chlorophyll-protein complexes affect membrane stacking, they
use low-temperature fluorescence emission and excitation spectroscopy to characterize these complexes. The authors
complement this work with mild denaturing electrophoresis and immunodetection
of the chlorophyll-protein complexes. In
summary, the authors propose a theoretical
model of the membrane changes during
grana development and greatly contribute
to our understanding of chloroplast and
thylakoid biogenesis.
Gregory Bertoni
Science Editor
[email protected]
ORCID ID: 0000-0001-7977-3724
828
The Plant Cell
REFERENCES
Austin II, J.R., and Staehelin, L.A. (2011).
Three-dimensional architecture of grana and
stroma thylakoids of higher plants as determined by electron tomography. Plant Physiol. 155: 1601–1611.
Daum, B., and Kühlbrandt, W. (2011). Electron
tomography of plant thylakoid membranes.
J. Exp. Bot. 62: 2393–2402.
Kowalewska, Ł., Mazur, R., Suski, S., Garstka, M.,
and Mostowska, A. (2016). Three-dimensional
visualization of the tubular-lamellar transformation of the internal plastid membrane network
during runner bean chloroplast biogenesis. Plant
Cell 28: 875–891.
Shimoni, E., Rav-Hon, O., Ohad, I., Brumfeld, V.,
and Reich, Z. (2005). Three-dimensional organization of higher-plant chloroplast thylakoid
membranes revealed by electron tomography.
Plant Cell 17: 2580–2586.
3D Visualization of Thylakoid Membrane Development
Gregory Bertoni
Plant Cell 2016;28;827-828; originally published online March 21, 2016;
DOI 10.1105/tpc.16.00230
This information is current as of June 18, 2017
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References
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