First published online July 21, 2003
doi: 10.1242/10.1242/dev.00619
SCD1 is required for cell cytokinesis and polarized cell expansion in Arabidopsis thaliana
Tanya G. Falbel1,
Lisa M. Koch1,
Jeanette A. Nadeau2,
Jose M. Segui-Simarro3,
Fred D. Sack2 and
Sebastian Y. Bednarek1,*
1 Department of Biochemistry, University of Wisconsin-Madison, 433 Babcock
Drive, Madison, WI 53706, USA
2 Department of Plant Biology, Ohio State University, 1735 Neil Avenue,
Columbus, OH 43210, USA
3 Department of Molecular, Cellular and Developmental Biology, University of
Colorado, Boulder, CO 80309, USA
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Fig. 1. Wild-type and cytokinesis-defective guard cells. (A-C) Stoma-specific
expression of KAT1-GUS, a marker for guard cell identity
(Nakamura et al., 1995 ), in
the cotyledons of 5-day-old seedlings germinated in the absence (A) or
presence (B,C) of 5 mM caffeine, an inhibitor of cell plate membrane
consolidation. scd1-1 mutant guard cells phenocopy the effects of
caffeine. (D-F) Light microscopy of Toluidine Blue-stained scd1-1
leaf epidermis from plants grown at 22°C. (G,H) KAT1-GUS
was expressed in cytokinesis-defective scd1-1 guard cells. Hanging
pores are indicated by arrows. A torus and oblate type guard cell are shown in
F and H, respectively. Scale bars: 10 µm.
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Fig. 2. Defective stomata are binucleate. Cotyledons of 13-day-old wild-type (A)
and scd1-1 seedlings (B,C) that express the nuclear (green) GFP N7
marker and (D) cotyledons from 4-day-old seedlings expressing plasma membrane
GFP 29-1 marker (Cutler et al.,
2000). Multinucleate scd1-1 epidermal cells with wall
stubs (arrow) are shown in C and D. Two serial confocal optical sections were
merged to create C. Cell walls were stained with propidium iodide (red) and
chloroplasts are autofluorescent (blue). (D) The membrane in the cell wall
stubs of cytokinesis-defective scd1-1 epidermal cells was contiguous
with the plasma membrane. Scale bars: 10 µm.
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Fig. 4. The scd1-1 mutant is temperature-sensitive. (A) scd1-1
plants grown under continuous illumination at 22oC (left) and
16°C (right). (B) Aborted scd1-1 flower buds from plants grown at
22°C. (C) The fertile inflorescences of plants grown at 16°C. (D,E)
Toluidine Blue stained leaf epidermal peels from plants grown at 22°C (D)
show many defective guard cells whereas plants grown at 16°C (E) show
normal guard cells and an increased number of meristemoids. (F)
Temperature-shift experiment. scd1-1 flower buds that were developing
during the 16°C incubation period (bracket) developed into fertile
flowers, which produced siliques filled with scd1-1 seed. Upon return
to restrictive conditions (22°C), flower bud development aborted once
again. (G) Three-month-old scd1-3 mutant grown in soil at 18°C.
Scale bars: 1 cm (A); 0.5 cm (B,C); 10 µm (D,E); 0.25 cm (G).
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Fig. 3. scd1 mutants display a dwarfed phenotype. (A) scd1-1,
scd1-2 and scd1-3 mutants grown on MS-Suc under continuous light
for 8 days are smaller, have shorter roots, and have darker green leaves than
those of wild type. (B) Mutant shoots are smaller and darker green than wild
type. (C) Comparison of wild type, scd1-1 and scd1-2 root cell size.
Cell length was plotted as a function of the distance from the root tip. Each
point represents an average of 20-50 cell measurements of a mixture of
epidermal and cortical cells. (DH) Root hair development in wild type and
scd1 mutant seedlings grown vertically on the surface of MS-Suc
medium. (D) Stereomicroscope image of surface views of a wild type (WT) and a
scd1-2 root. (E-H) Phase contrast images of (E-G) scd1/2 and
(H) wild-type roots. scd1 mutants usually form small blebs (D,E,F) at
the basal end of trichoblasts, which do not extend. (E) Enlargement of boxed
area in D. Arrows in G indicate branched root hairs. Scale bars: 1 cm (A);
0.25 cm (B); 100 µm (D-H).
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Fig. 8. Effects of vesicle and cytoskeletal inhibitors on wild type and
scd1 root growth and cell morphogenesis. CLSM optical sections of
wild type (wt), scd1-1 and scd1-2 roots grown in (A) the
absence and (B-E) the presence of caffeine (B), brefeldin A (C), latrunculin B
(D) and propyzamide (E). The graph associated with each image represents the
extent of root growth (y-axis; mm) over a 4- to 5-day period in the
absence and presence of the inhibitors at the indicated concentrations
(x-axis). The asterisk denotes the inhibitor concentration used in
the underlying root section. 5-15 seedlings were measured for each treatment
and genotype. Scale bars: 50 µm.
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Fig. 6. RT-PCR analysis of SCD1 expression in wild-type and mutant tissue.
RT-PCR analysis of SCD1 mRNA expression in total RNA isolated from
wild-type roots, rosette leaves, cauline leaves, immature flower buds, open
flowers, scd1-1 leaf tissue, and actively dividing
suspension-cultured cells (T87). A reaction (-) containing no DNA template was
included as a negative control. RT-PCR amplified ubiquitin was used as a
loading control. std: 1.0 and 0.5 kb markers.
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Fig. 7. scd1::T-DNA mutants showed defects in leaf trichome and epidermal
pavement cell expansion. (A) wild type and (B) scd1-2 cotyledon
epidermal cells stained with propidium iodide. The white arrowhead indicates a
potential recently divided guard mother cell. (C) Wild-type and (D-G)
scd1-2 leaf trichomes on emerging leaves. (E) An enlarged view of
expanding unbranched scd1-2 trichome initials. (F,G) Older leaves of
scd1-2 seedlings showing mechanically unstable trichomes and small
gaps between pavement cells (arrowheads). Cell debris is often observed in
craters surrounded by the subtending socket cells of broken trichomes. (H,I)
Transmission electron micrographs of cells from very young leaves; (H) a
wild-type telophase cell and (I) a cytokinesis-defective scd1-2 cell.
C, chloroplast; CP, cell plate; CWS, cell wall stub; PCW, parental cell wall;
G, Golgi; M, mitochondrion; N, nucleus; V, secretory vesicles. Scale bars: 10
µm (A,B); 50 µm (C-G); 1 µm (H,I).
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© The Company of Biologists Ltd 2003
