全 文 ：Received 26 May 2003 Accepted 22 Oct. 2003
Supported by the National Natural Science Foundation of China (60050003).
* Author for correspondence. Tel: +86 (0)10 62591431 ext. 6239; E-mail: .
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Plasmodesmatal Dynamics in Both Woody Poplar and Herbaceous Winter
Wheat Under Controlled Short Day and in Field Winter Period
JIAN Ling-Cheng*, WANG Hong
(Key Laboratory of Photosynthesis and Molecular Environmental Physiology, Institute of Botany,
The Chinese Academy of Sciences, Beijing 100093, China)
Abstract: Electron microscopic observation revealed that poplar (Populus deltoides Marsh.) and winter
wheat (Triticum aestivum L. cv. Seward 80004) plasmodesmatal structures significantly changed under
short day (SD, 8 h light) and in winter period, and such changes differed also noticeably between these two
woody and herbaceous plants. Under long day (LD, 16 h light), many plasmodesmata with strong stain
appeared in the cell wall of both poplar apical buds and winter wheat young leaf tissues, and connections of
cytoplasmic endoplasmic reticulum (ER) with the ER in some plasmodesmata were observed. In addition,
the typical “neck type” plasmodesmata were observed in winter wheat young leaf tissues, and their central
desmotubules (appressed-ER) could be clearly identified. Under SD, many poplar plasmodesmata showed
only a partial structure in the cell wall and appeared to be discontinued; some plasmodesmata swelled in the
mid-wall, forming the cavity, and no appressed-ER appeared. In winter wheat, however, no noticeable
alterations of plasmodesmata occurred, and the plasmodesmatal structure essentially remained the same
as it was under LD. In winter period, poplar plasmodesmata had a similar morphology as those observed
under SD, however, winter wheat manifested at least two types of significant plasmodesmatal alterations:
one plugged by electron-dense materials and the other of reduced neck region compared to those under
LD. The above dynamic difference of the two species plasmodesmata under SD and winter period revealed
the difference of their dormancy development under those environmental conditions.
Key words: plasmodesmata; plant dormancy; macromolecular intercellular trafficking; poplar; winter
wheat
Plasmodesma is a supracellular structure of plants (Lucas
et al., 1993). It converts the colonies of independent cells
into an interconnected symplast system, and also provides
a direct cell-to-cell cytoplasmic pathway for substance
transport and message transference. Plasmodesmata are
highly dynamic in terms of their biogenesis, structural modi-
fications and transport functions. They can be formed at
cytokinesis, or de novo across existing cell walls (secondary
plasmodesmata), and can be further modified to reduce or
enhance intercellular transport (Lucas et al., 1993; Ding et
al., 1999).
Plasmodesmata play important roles in coordinating gene
expression and cellular processes that lead to regulating
cell division and differentiation, morphogenesis, growth
and development, and other specialized functions includ-
ing the responses and adaptation of plants to environmen-
tal changes (Lucas et al., 1993; Ding et al., 1999). In our
previous study, we have noticed that the constriction and
blockage of the plasmodesmata in poplar apical buds dur-
ing short day induced dormancy development (Jian et al.,
1997). This study is about the plasmodesmatal dynamics in
poplar during short days and over winter period in com-
parison with winter wheat, a herbaceous plant which does
not develop “physiological dormancy” during short day
and over-winter period (Kacperska-Palacz, 1978). The re-
sults further demonstrated that the plasmodesmata are
closely related to the dormancy of plants.
1 Materials and Methods
1.1 Plant materials
Poplar plants (Populus deltoides Marsh.) were estab-
lished by cuttings and raised individually in 1.5 L pots with
a mix of 2:1:1 (V/V/V) of peat moss/soil/prolite in a green-
house with a regime of 16 h light (long day, LD) and 25/21
℃ (day/night) temperatures. When plants were about 40-
50 cm tall, they were divided into three groups: one re-
mained in the greenhouse; one was transferred into an 8 h
light (short day, SD) growth chamber with 25/21 ℃(day/
night) temperatures for 35 d growth; the 3rd one was trans-
planted in the field in late August (45° N, St. Paul, Minnesota,
Acta Botanica Sinica
植 物 学 报 2004, 46 (2): 230-235
JIAN Ling-Cheng et al.: Plasmodesmatal Dynamics in Both Woody Poplar and Herbaceous Winter Wheat Under Controlled
Short Day and in Field Winter Period 231
USA). Winter wheat (Triticum aestivum L. cv. Seward 80004)
seedlings were also cultured under the same three condi-
tions as the poplar plants: (1) Wheat seeds were planted in
pots and grew in the above mentioned same greenhouse;
(2) When the seedlings reached a 3-leaf stage, they were
transferred into the above mentioned same SD growth cham-
ber for 35 d; (3) In early September, wheat seeds were planted
in the field, where poplar plants were grown.
1.2 Sample preparation for electron microscopic obser-
vations
Apical buds of poplar and young leaves of winter wheat
were collected from plants grown in the greenhouse, the
growth chamber, and the field winter period. Tissues were
cut into 0.5 mm×0.5 mm slices. The slices were immedi-
ately immersed in a fixative containing 3% paraformalde-
hyde and 4% glutaraldehyde in 50 mmol/L sodium cacody-
late buffer (pH 6.5) at 4 ℃ for 6 h. After fixation, samples
were washed four times, 15 min each, with the same buffer
at 4 ℃, and then post-fixed in 2% osmium tetroxide (OsO4)
in the same buffer at 4 ℃ for 4 h. After washed, samples
were dehydrated through a series of ethanol, and then em-
bedded in Spurrs resin (Spurr, 1969). The embedded
samples were sectioned with a diamond knife and an RMC
(Tucson, AZ, USA) MT 4000 ultramicrotome. Sections were
stained with uranyl acetate and lead citrate, and examined
and photographed with a Philips CM12 transmission elec-
tron microscope (F. E. I. Company, Tacoma, WA, USA)
operated at 60 kV.
2 Results
2.1 Plasmodesmata in plants grown under LD
Electron microscopic observations revealed that many
plasmodesmata existed in the cell walls of poplar apical
buds cells grown in the greenhouse with 16 h photoperiod
(long day, LD) and 25/21 ℃ (day/night) temperatures (Figs.
1, 2). The plasmodesmata appeared to be strongly stained.
As shown in Fig.2, a cytoplasmic endoplasmic reticulum
(ER) was connected to the ER in the plasmodesma
(arrowheads). Under the same LD conditions, there also
appeared many plasmodesmata in the cell walls of winter
wheat young leaf tissues (Figs.3, 4). The connection of
cytoplasmic ER with the appressed ER in some plasmodes-
mata could be found, too (Fig.3, arrowheads). And a “neck”
phenomenon could also be observed at both the ends of
some plasmodesmata (Fig.4), in which the central
desmotubule (appressed ER) could be clearly identified.
Figs.1-4. The plasmodesmata in both poplar (Figs.1, 2) and winter wheat (Figs.3, 4) grown under LD. A strongly stained appearance
shown in these plasmodesmata. Some cytoplasmic ER connection with the ER in the plasmodesmata can be observed (Figs.2, 3,
arrowheads). Fig.4 shows a “neck type” plasmodesmata, in which the central desmotubule (appressed ER) may be clearly identified. 1.
× 28 000. 2. ×42 000. 3. ×32 000. 4. ×60 000.
Acta Botanica Sinica 植物学报 Vol.46 No.2 2004232
Figs.5-12. 5-8. Plasmodesmata in plants grown under SD. 5, 7. Discontinued plasmodesmata appeared in poplar cell walls. Middle
part of the plasmodesmata widened and became empty in the mid-wall (Fig.6, arrowhead). 8. Plasmodesmata in wheat young leaf tissues.
The plasmodesmal structure did not show obvious alteration. 5-8. × 38 000. 9-12. Plasmodesmata in plants grown winter. 9, 10.
Poplar plasmodesmata. Discontinued-partial plasmodesmata showed up in the cell wall, and the middle parts of some plasmodesmata
widened and emptied in the mid-wall (Fig.10) as it showed in the SD grown sources (Figs.5-7). × 38 000. 11, 12. Winter wheat
plasmodesmata. An electron-dense material was located at the orifices of the plasmodesmatal necks (Fig.11). 11. ×40 000. 12. ×30 000.
JIAN Ling-Cheng et al.: Plasmodesmatal Dynamics in Both Woody Poplar and Herbaceous Winter Wheat Under Controlled
Short Day and in Field Winter Period 233
2.2 Plasmodesmata in plants grown under SD
The plasmodesmata in poplar apical buds cells grown
under short day (SD) showed an obvious alteration com-
pared with those in poplar grown under LD. Many partial
plasmodesmata manifested in the cell walls (Figs. 5-7), in-
dicating that these plasmodesmata were discontinued in
the cell walls. The phenomenon was confirmed through a
serial sectioning and a large number of section
observations, and the middle-part of plasmodesma was
widened and emptied in the mid-walls (Figs. 6, 7,
arrowheads). The channels of the most of plasmodesmata
were not stained. No desmotubules were seen in the plas-
modesmata (Figs.6, 7).
In wheat young leaf tissues grown under SD, the
plasmodesmal structure did not show obvious alteration.
No disconnection of plasmodesma occurred (Fig.8).
2.3 Plasmodesmata in plants grown in field winter period
The plasmodesmata in poplar apical buds grown in win-
ter period were similar to those observed under controlled
SD conditions with warm temperatures (Figs. 5-7, 9, 10). In
the cell walls, there also were many partial plasmodesmata
(Fig.9), and the middle parts of plasmodesmata widened
and emptied (Fig.10).
In winter wheat young leaf tissues, we did not observe
the discontinued plasmodesma, as it did in poplar. The
plasmodesmatal changes of winter wheat seedlings in win-
ter period occurred mainly at two aspects: one is that many
plasmodesmata were plugged by an electron-dense material.
As shown in Fig.11, the plugging material was located at
the orifices of the plasmodesmatal necks. The other is that
the average diameters of their neck regions (Fig.12) were
significantly reduced, compared with the plasmodesmata
grown under LD. Their average diameters were reduced
from 31 to 25 nm under LD.
3 Discussion
We had reported in 1997 that the constriction and block-
age of plasmodesmata in poplar apical buds during SD in-
duced dormancy development of plants (Jian et al., 1997).
In the present study, we further observed that in the cell
walls grown under controlled SD conditions, often only a
part of plasmodesma was found; many plasmodesmata were
discontinued in the cell walls. In natural mid-winter period,
the same phenomena also occurred. The findings show
that the plasmodesmal channels were discontinued, and
symplast was disconnected either under SD or in winter
period, which in turn may lead to the growth cessation and
dormancy development, and the plants would be able to
remain in a stable dormancy status during over-winter.
It was known that the over-wintering herbaceous plant
winter wheat did not develop into a true stage of the “physi-
ological dormancy” as woody plants like poplar (Kacperska-
Palacz, 1978; Jian et al., 2003). They restored growth rap-
idly after placed in a regime of LD and warm temperature.
This is also confirmed in the present study. In the cell walls
of winter wheat plants grown under SD and/or over
wintering, we did not observe any discontinued plasmodes-
mata (partial plasmodesma) as it occurred in poplar.
However, it was found that the neck region of the plas-
modesmata was constricted, more specifically, the average
diameter of the necks reduced from 31 to 25 nm, compared
with the plasmodesmata grown under LD. In addition, the
plasmodesmata were plugged by electron-dense materials
(Fig.11). We do not carry out further research on what is
the plugging material. Some other studies showed that the
plugging material could be a glycoprotein or callose (Hughes
and Gunning, 1980; Ding et al., 1992; Jian and Sun, 1992). It
was shown that a sphincter-like located in the cell wall im-
mediately surrounding the orifices of plasmodesmata was
involved in the regulation of plasmodesmatal transport
(Olesen and Robards, 1990; Badelt et al., 1994; Overal and
Blackman, 1996). Rinne and van der Schoot (1998) reported
that during the induction of birch seedling dormancy, the
closure of the plasmodesmata in shoot apical meristem might
be due to the sphincter formation and callose deposition in
the plasmodesmatal orifices. It seems to be reasonable to
deduce that when winter wheat seedlings were subjected
to winter low temperatures, the sphincter, callose and gly-
coprotein were accumulated in the plasmodesmatal
channels, which in turn led to the constriction and block-
age of the plasmodesmatal channels, and limited symplastic
transport and signal transferring, so plant growth was tem-
porarily inhibited. When the ambient temperature became
warm, either the constriction or the plugging could be
readily vanished, and thus plant growth was restored
rapidly, which did not like poplar that has a stage of physi-
ological dormancy.
We also noticed another interesting phenomenon when
sample sections of poplar and winter wheat were stained.
Under LD, the degree of plasmodesmatal staining tended
to be much stronger than those under SD and over winter-
ing for poplar and than that in winter period for winter
wheat. It has been known that plasmodesmatal transport
materials contain not only small-molecules, but also
macromolecules, such as proteins and nucleic acids (Mezitt
and Lucas, 1996; Ghoshroy et al., 1997; Ding, 1998). The
increasing evidence revealed that the macromolecular trans-
port via the plasmodesmata plays an important role in
Acta Botanica Sinica 植物学报 Vol.46 No.2 2004234
mediating and controlling the intercellular communication
and the gene expression during plant growth and
development. (Heinlein, 2002; Jian et al., 2003). We specu-
late here that the stronger stain of plasmodesmata under
LD may be the appearance of the macromolecules in inter-
cellular trafficking via the plasmodesmata. Under SD and/
or over wintering, the macromolecular intercellular traffick-
ing was slowed down or even stopped, as a result, the
stained plasmodesmata weakened, or even no stain materi-
als were observable in the plasmodesmatal channels.
Acknowledgements: Bulk of this work was carried out in
the laboratory of plant hardiness, Department of Horticul-
tural Science and Plant Biological Science Program, Uni-
versity of Minnesota, St. Paul, MN 55108, USA.
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