Morphology of Gametophytes and Young Sporophytes of Sphaeropteris lepifera

11 Pages·2000·5.2 MB·English

by  Yao-Moan Huang

American
Fern
Journal 90(4j:127-137
(2000J
Morphology
of Gametophytes and Young
Sporophytes
of Sphaeropteris
lepifera
Yao-Moan Huang
Department
of Forestry, National Taiwan University, 1, sec. 4, Roosevelt Rd„ Taipei 106, Taiwan
Shao-Shun
Ying
Department
of Forestry, National Taiwan
University, 1, sec. 4, Roosevelt Rd., Taipei 106, Taiwan
Wen-Liang
Chiou^
Division of Forest Biology, Taiwan Forestry Research 53 Nan-Hai
Institute, Rd.,
Taipei Taiwan
100,
AhsiracL—
Sphaeropteris one On
lepifera is of the largest tree ferns in Taiwan. average, produces
it
50.7 sporangia per sorus, and 64 spores per sporangium. Spore germination,
after 2 years of storage
4°C was over 95%. The
at pattern of spore germination was "Cyathea-type", and
the gametophytes
exhibited mainly Drynaria-type development with occasional Adiantum-type
development. Typ-
ical gametophytes were heart-shaped but had
the potential elongate and become
to
elliptical.
Multicellular hairs on the dorsal and
ventral surfaces of the midrib cushion increased and
in size
changed shape with They when
age. w^ere usually uniseriate young, and became
muhiseriatc with
Gametophytes
age. initiated antheridia about 1 month after spores were sown, and did not become
hermaphrodites weeks
until 7 later. During ontogeny, the gametangial sequence was from male
the
to hermaphroditic. Antheridia formed on the wings of the ventral and dorsal surfaces of gameto-
The
phj^es. wall of each antheridium was composed
of 5 cells. Archegonia appeared on the
cushion of the ventral surface of gametophytes. Some gametophytes
initiated clone-formation
When
through
vegetative regeneration. sufficient water was provided, young sporophytes began
appear weeks
to 12 after spores were sown. The fronds were The
first midribless. uniseriate,
multicellular hairs on young sporophytes were similar to those on gametophytes.
:emiination
types of early development, trichomes, and gametangia, have been used
to
taxa
and
Kaur, 1971; Atkinson, These
1973]. characteristics provide information
relevant to fern phytogeny Nayar and Kaur, 1971] and the ecology and
(e.g.,
reproductive biology of different species [Chiou and Chiou
Farrar, 1997a,
b; et
Masuyama,
aL, 1998; 1975a,
b, 1979].
In the Cyatheaceae, spore germination Cyathea-type and gametophyte
is de-
velopment
Adiantum-type
is or nearly Drynaria-type (Nayar and Kaur,
1971].
Gametophytes
are long-lived (2-6 years] and tend elongate with
to slightly
age.
The
multicellular, bristle-like hairs that appear on gametophytes
in family
this
indicate the Cyathaceae
phylogenetically Loxsomaceae
is close to the (Atkin-
same
gametophytes, with some
vigorous gametophytes being
strictly archegonial
Apogamy
was
(Stokey, 1930]. reported some
in species in the Cyatheaceae
Corresponding
author.
'
AMERICAN FERN VOLUME NUMBER
JOURNAL:
128 90
4 (2000)
Table L Spore sources, usage, culture medium and storage period.
Stored
Medium
Spores Location Observation (years)
m
Huang 25 Wulai, 370 sporangium and spore number
m
Huang 26 Wulai, 370 sporangium and spore number
m
Huang 27 Yamingshan, 250 sporangium and spore number
m
Huang
25 Wulai, 370 germination agar
rate
m
Chiou 14495 Wulai, 150 germination agar 2
rate
m
Chkni 14787 Hsinihsien, 200 germination agar
rate
1
m
Huang
25 Wulai, 370 gametophyte morphology peat
m
Huang
26 Wulai, 370 gametophyte morphology
peat
m
Huang 27 Yamingshan, 250 gametophyte morphology
peat
(Slokey, 1918), but Walker (1966) reinvestigated two of these species and found
them
be sexual
to diploids.
Spbaeropteris Tryon and one
lepifera (Hook.) (Cyatheaceae) the of
largest,
is
Wang
the most abundant, species in this family in Taiwan. et (1977) de-
al.
scribed sporophyte morphology, epidermal and
its scales, stomata, cells, the
anatomy of the stipes and trunks. However, except for the gametangial se-
quence (Masuyama,
gametophyte
1975b)» characteristics of the of S. lepifera
have been
not described.
The number
sporangium
of spores per has also been used in the systematic
classification of ferns (Sen, 1964; Gastony, 1974). Spore gametangial
viability,
sequence, and gametophyte growth important components
habits are of fern
reproductive biology (Chiou and Farrar, 1997a; Chiou et al, 1998). Complex
among may
interactions gametophytes multispore
in cultures the
affect se-
quence gametangial development
of in individual plants. Detailed analysis of
sexual and
status, in relation to the age size of gametophytes, essential for
is
determining the most probable breeding system employed by
S. lepifera
(Chiou and Chiou The
Farrar, 1997b; et al, 1998). present study explores spore
m
ogy and growth habits of the gametophytes and the morphology of young spo-
rophytes
of
S. lepifera.
Materials and Methods
Spores were collected from sporophytes growing on mountain
slopes in
northern Taiwan
(Table Voucher specimens were deposited Herbar-
in the
1).
ium
Taiwan
of Forestry Research Institute (TAIF). Spores were stored in the
refrigerator
at 4°C.
The number
of sporangia per sorus (from 50 randomly sampled per
sori
and number
plant) the of spores per sporangium (from 50 randomly sporangia
estimated
medium
spores stored 4°C one two was
at for or years assessed Spores were
(Table
1).
with 2.5%
sterilized Clorox for 5 min, rinsed with water 10 min.
sterilized for
HUANG
GAMETOPHYTES AND
ET SPOROPHYTES OF SPHAEROPTERIS
AL.:
129
Mean
Tari
f 2. geiniination (%) of fresh and stored (4°C) S. lepifera spores sown on agar medium.
Days sowing
after spores
Storage _
(years) 5 9
7
11
0.0 (0) 81.2 (7.2) 96.7 (4.0) 99.0(1.2)
1 35.8 (26.0) 97.9 (2.0) 98.7 (1.5) 98.9 (1.5)
2
1.3 (1.9) 29.7 (16.8) 84.0 (7.4) 95.4 (4.0)
Standard
error in parentheses.
and then sown on 1.1% medium and
agar-solidified containing Gantt
Arnotts'
1%
(1965) mineral nutrients and one drop of FeCl3 per 400 ml medium.
of
pH
The media
of the ranged from 5,0-5.2. Germination were estimated
rates
from agar-medium
six petri dish cultures with 50 spores per dish. Rupture of
was
the spore wall used as an indicator of germination. Gametophyte mor-
phology was observed months. The and
for 8 sexual expression, age size of 50
gametophytes from each of 3 multispore peat cultures were recorded every 2
weeks. Gametophyte width was measured
at the widest point.
medium
Because the peat provided conditions more
similar to those in the
medium,
field than the agar gametophyte morphology and sexual expression
were assessed only gametophytes peat-grown However, game-
for in cultures.
medium
tophyte cultures on agar were used estimate germination because
to
spores and their germination status could be seen more easily on agar medium.
were maintained under
All cultures at 20-25''C white fluorescent illumination
1000-1500
of lux for 12 hrs per day.
Microscopes (Lecica, Wild M8; Leitz, Dialux 20) were used to make mor-
phological observations of gametophytes and young sporophytes. Pictures
made
were with the aid of a drawing tube or photomicrography. Gametangia
were also observed with a scanning electron microscope. Gametophytes were
dry mounted on double-stick mending coated with and observed
tape, gold,
with a Hitachi S2400 Scanning Electron Microscope.
Results
The number ±
and
of sporangia per sorus averaged 50.7 13.1 ranged
s.d.
from 19 Each sporangium contained 64
to 78. spores.
mm
began about 5 days after sowing, whereas germination of fresh spores did not
begin until seven days after sowing. The viability of spores maintained for one
two was
or years in cold storage not significantly less than that of fresh spores.
Two 95%
weeks after sowing, over of fresh and stored spores had germinated
(Table
2).
Wh
lepifera are tetrahedral.
rupt
formed
and did not contain The second was
chloroplasts. division perpendicular
to
AMERICAN FERN VOLUME NUMBER
130 JOURNAL:
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4
(2000)
Morphology
Figs. 1-9. of different stages of S. leplfera gametophytes. Figs. 1-3. Spore germi-
A
A
nation. 4-6. Filamentous
Figs. stages. Fig. 7. spatulate gametophyte. Fig. filament with a
8.
mm
A
wedge-shaped
=
apical cell. Fig. 9. hleeaarrtt--sshhaappeedd gametophyte. Bar 50(jLm for Figs. 1-8; 1
g;
for Fig.
9.
the division and, by
first (Fig. 3) a series of transverse divisions, initiated a
uniserlate filament was 4-8
that usually cells long (Figs. 4-8). About 4 days
after spore germination, the apical, and sometimes subapical, divided
cells
parallel to the long axis of the filament However, few gameto-
(Fig. in a
5).
phytes
the apical cell of the filament became sluggish and did not divide
(Fig.
This was pushed
apical
6). cell to the subapical margin by intercalary divi-
When
sions. Next, a spatulate plate formed. gametophytes were about
5 cells
wide, wedge-shaped
a meristematic formed
cell in the apical region
(Fig.
7).
some
underwent
(Fig. that repeated oblique was
8] divisions until replaced by a
it
pluricellular meristem, which
the cells of divided producing
actively, a
mi
me
phyte formed The
wings were
(Fig. 9). one cell thick and were usually
flat,
some
but curved upward
at the margin. Rhizoids were restricted mostly the
to
ventral surface of the midrib. They were transparent but became brown
light
brown
with
to
age.
Gametophytes
initiated antheridium production
in the spatulate stages (<0.5
mm
wade). In heart shaped gametophytes,
antheridia usually appeared on the
ventral surface of the wings with few forming on
(Fig. a
9), the dorsal surface.
the apical notch had
If not formed, antheridia sometimes formed
near the api-
cal region on
(Fig. or the margin, on
17), especially filamentous
proliferations
Mature
(Fig. 20). antheridia were about 50 wide and 40 jxm high
jjim (Fig. 10).
The
antheridium was
wall composed
of five cells: a basal cell, a lower ring
an upper
cell, ring cell, a crescent-shaped and an
cell, elliptical opercular
cell.
Upon
dehiscence,
the opercular was thrown
cell and sperm were
off, released.
Gametophytes
did not produce
archegonia weeks
until 7 spore sowing
after
mi
observed
HUANG
ET GAMETOPHYTES AND SPOROPHYTES OF SPHAEROPTERIS
AL.:
131
50u»
X
15K'-.'
1 .
•
SEM
An An
Figs. 10-11. of S. lepifera gametangia. Fig. 10. antheridium. Fig. 11. archegonium.
Mature archegonia were about 40 wide and 50 jxm high and
jjim (Fig. 11], the
neck was 4 to 5 cells long. Antheridia continued to form after archegonia were
mm
Male gametophytes were usually than wide, whereas
initiated. less 3 her-
mm
maphroditic gametophytes were usually greater than 3 wide. By 11 weeks
after spore sowing, all gametophytes bore antheridia, that they were male
is
hermaphroditic
or (Table
3].
Trichomes occurred on both and
the dorsal ventral surfaces of the gameto-
phyte midrib. Usually, they were mixed with the archegonia on the cushion,
especially near the apical notch of the gametophyte. Trichomes did not appear
until the cushion and archegonia formed. The size of the pluricellular hairs
varied Those on young gametophytes were
greatly. uniseriate occasionally,
or,
and were composed
bi- or triseriate (Figs. 12, 13], usually of less than 20 cells.
Hairs began as uniseriate structures that grew by intercalary division into larg-
On
with gametophytes months
multiseriate structures age. older 8
er, (e.g.,
old), the hairs could grow to 8 cells wide and be comprised of more than 50
which were with
cells in total, a uniseriate, needle-like tip (Fig. 14].
Some
gametophytes and became
of elongated they
S. lepifera elliptical as
aged (e.g., 15 weeks old) (Figs. 15-17). Older gametophytes often became pale,
or even necrotic, at their posterior end but kept growing at their anterior end.
Some many
were slender, with antheridia, but without archegonia or an ap-
parent apical meristem. Other elongate gametophytes formed cushions
discrete
(Figs. 16, 17).
Some when
gametophytes began to produce vegetative proliferations they
were 13 weeks Daughter gametophytes formed from one few on
old. or a cells
the dorsal or ventral surfaces or on the margin Each of the daughter
(Fig. 18).
gametophytes developed a pluricellular meristem and gametangia and even-
produced Some many
tually large clones. gametophytes formed filamentous
one wide produced
proliferations, to several cells (Fig. 20], that only anther-
idia. Occasionally, the anterior wings of gametophytes elongated and prolif-
As
them
erated (Fig. 19). proliferations grew, their posterior died, separating
from the parent gametophyte.
AMERICAN FERN VOLUME NUMBER
132 JOURNAL:
90
4 (2000)
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HUANG ET GAMETOPHYTES AND SPOROPHYTES OF SPHAEROPTERIS
AL.: 133
Figs. 12-29. Morphology of gametophytes and juvenile sporophytes of S. lepifera. Figs. 12-14.
Multicellular hairs of ganietophytes. Figs. 15-17. Elongate gametophytes. Figs. 18, 19. Gameto-
phytes with Filamentous with 21-24. Mid-
proliferations. Fig. 20. proliferation antheridia. Figs.
rihless few fronds. Figs. 25-27. Midribbed fronds. Fig. 28. Unicellular hairs of a young spo-
first
=
rophyte. Fig. 29. Multicellular hair of a young sporophyte. Bar 100p.ni for Figs. 12-14,
28, 29;
mm mm mm
15-17, 21-27;
0.2 for Fig. 20; 1 for Figs. 2 for Figs. 18, 19.
134 FERN VOLUME
JOURNAL:
sufficient
peared
in peat cultures about 12 weeks after spore sowing. The gametophyte
usually senesced and
disappeared
after the sporophyte formed. However, some
gametophytes with young
a sporophyte formed
produced
proliferations that
additional sporophytes. Laminae of the few fronds of young sporophytes
first
branched
dichotomously
(Figs. 21-24). Subsequent juvenile fronds were
pin-
nately divided
(Figs. 25-27). Except the few
for first fronds, unicellular hairs
and
were
scales evenly on
distributed the frond margin
25-29).
(Figs.
Discussion
Sen
noted
(1964) that the diagnostic
characters for the sporangia of most
simil
spores each sporangium
in 64 The
is or 16. sporangia of Lophosoria, Sphaer-
Metaxya
Nephelea
have
16 spores (Gastony,
1974). In this study, 64 spores were found
in lep-
S.
same number
ifera sporangia, the found
in the sporangia
of the majority
of
more
highly evolved
leptosporangiate ferns (Holttum and Sen, 1961; Gastony,
1974).
Page
(1979) reported that the spores of some Cyatheaceae
lost their viability
few
weeks,
after a but did not
describe the conditions under which were
they
stored. Germination of Cyathea delgadi was 20%
spores than
less years
after 2
of dry storage -12°C (Simabukuro
at
et al, 1998). However, the high germi-
lepifi
that
be dependent
on
the storage
conditions.
After
S. lepifera spores germinated,
the filament grew
along
the polar
axis,
while
the first rhizoid elongated along
the equatorial plane. This pattern of
spore
germination has been
classified as "Cyathea-type" and considered
is
typical of ferns in the Cyatheaceae
(Nayar and
Kaur,
1971).
Using
the
definitions of Nayar and Kaur
gametophyte
(1971), S. lepifera de-
velopment was
mostly
of the Drynaria-type, but with some Adiantum-type
Our
features. somewhat
results are
from
different those of Nayar and Kaur
who
"
S
(1971), described
'
lepifi
or nearly
Drynaria-type.
if'
became
more
elongated.
Elongate
gametophytes were and more
paler
slender
than
heart-shaped
gametophytes, and some
remained
in the antheridial
stage
months.
for Stokey
8 (1930) reported
that elongate gametophytes
Cyathea
of
arborea were much
very pronounced
and
produced when
only
antheridia they
lepifi
gametophyt
developed
being
after overgrown by
other gametophytes.
This simulates
partial
which may
burial, occur
in nature. Although
elongate gametophytes
are in-
HUANG
GAMETOPHYTES AND
ET SPORGPHYTES OF
AL.: SPHAEROPTERIS
135
capable of supporting sporophytes, they may play
a significant role in provid-
sperm and
ing thus promoting
cross-fertilization.
In the Cyatheaceae, the antheridial wall usually composed
of but
is 5 cells,
some
variation occurs (Stokey, 1930; Atkinson and Stokey, 1964]. The wall of
each antheridum was
of S. lepifera in this study always comprised of
5 cells,
including
a basal cell, 2 ring cells, a crescent-shaped and an
cell elliptical
was
opercular that usually shed The
cell at antheridial dehiscence. archego-
nium
neck more
been
is straight, or less, as has reported for other Cyatheaceae
and some advanced
less ferns (Stokey, 1930; Atkinson and Stokey,
1964).
The
peculiar, multicellular hairs on the archegonial cushion game-
of the
tophyte are characteristic of Cyatheaoid gametophytes
(Stokey, 1930). Outside
the Cyatheaceae, similar multicellular hairs are found only on gametophytes
Loxsomaceae
in the (Stokey, 1960; Atkinson and Homology
Stokey, 1964). of
the multicellular hairs on gametophytes in the Cyatheaceae and Loxsomaceae
supported by molecule-based
is cladistic analysis (Pryer et aL, personal com-
munication).
Gametophytes
of S. lepifera can produce large clones and enhance
their
by
longevity vegetative growth, as has been described for some other species
many
in the Cyatheaceae and other fern taxa (Stokey, 1930; Atkinson and
Sto-
key, 1964; Chiou and Farrar, 1997a). The type of vegetative regeneration
pre-
lepifi
gametophyt
Atkinson and Stokey They
suggested
(1964). that this type of vegetative regen-
eration usually occurred on old or injured gametophytes. However, many
clones of S. lepifera formed from gametophytes that were green and very
new
Although
healthy. each gametophyte could produce male and female gam-
few produced
etangia, sporophytes while attached to the parent gameto-
still
phyte if the parent plant had produced a sporophyte. Perhaps, the developing
embryo
of the parent gametophyte
inhibited the fertilization of eggs of the
daughter gametophytes, or inhibited zygote development
in fertilized eggs.
further investig
lepifi
Most
mm
mal
only gametophytes were 0.5-3.0 wide, and hermaphroditic
i
mm
gametophytes were more
usually than 3.0 in width. antheridium
Initial
formation was followed by the attainment of prolonged hermaphroditic
a
phase during which antheridia continued However,
to form. in a previous
study of the gametangial sequence of [= Cyathea
S. lepifera lepifera), anther-
idium formation ceased once plants became hermaphroditic (Masuyama,
Gametophyte may
1975b). sexual expression be by
affected the culture medi-
um
Masuyama
(Masuyama,
1975a). (1975b) observations were on gameto-
s
phytes grown on agar medium, whereas gametophytes in study were
this
on medium.
grow^n peat
A
gametangial sequence from male hermaphroditic may
to favor
intraga-
metophytic Masuy
selfing (Klekowski, 1969;
lepifi
AMERICAN FERN JOURNAL: VOLUME NUMBER
136 90 4 (2000)
Based on isozyme Chen suggested mating system
data, (1995] that the of
S.
lepifera tended toward intergametophytic crossing. Similarly, three other tree
ferns, Alsophila firma (Cyatheaceae), Cyathea stipularis (Cyatheaceae) and Lo-
phosoria quadripinnata (Lophosoriaceae) are outcrossing (Soltis et ah, 1991).
may
been
has suggested that inbreeding of bisexual gametophytes be limited
It
by high genetic load (Klekowski, 1969, 1973; Masuyama, 1979; Peck et ah,
common
Hooper and
1990; Haufler, 1997). Thus, bisexual gametophytes are
if
may
in natural populations of genetic load be the most important
S. lepifera,
factor favoring outcrossing in
S. lepifera.
Young sporophytes were produced when water was supplied
sufficient to
mature Gametophytes would when
sexually plants. not bear sporophytes water
was
not added to cultures, although they had mature gametangia. In addition,
young sporophytes were always born on
the archegonia, suggesting that
S.
sporophytes from The
lepifera likely resulted 64-spore sporangi-
fertilization.
um
also indicates that not an apogamous species.
it is
In S. lepifera, the blades of juvenile leaves are dichotomously branched,
whereas
those of succeeding juvenile fronds pinnately This
are dissected.
is
common
most
the type of frond ontogeny in leptosporangiate ferns (Wagner,
1952).
Acknowledgments
The
authors thank two anonymous reviews comments, Alan Warneke
for their useful Dr. for
SEM
editing the manuscript, and Miss Chien-Rong Huang was
for assistance. This research sup-
Forestry
Research
Institute (contribution No.
137).
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