Red Light Inhibition of Spore Germination in Lycopodium clavatum

2008·2.5 MB·English

by  Dean P Whittier

Red
Light Inhibition of Spore Germination
in
Lycopodium
clavatum
velop surficial, photosynthetic: gamotophytes following spore germination. However,
species, including Lycopodium clavatum, give rise to subterranean, nonphotosynthetic,
lizal gametophytes and their spores germinate in the dark. Red light, like white light,
the germination of these spores. Crimination occurs after exposure to far-red light. The
if far-red light are reversed by red light and those of red light are reversed by far-red light
ing the involvement of photochrome. The active form of phytochrome, inhibits
Pfr,
tion in L. clavatum. It appears that this is a general phenomenon in seedless vascular
photoinhibition of germination by white or red light insures that these spores germinate
underground
in nature providing improved chances of spores obtaining adequate moisture
soil
and
mycorrhizal colonization young gametophytes
of that are essential continued development.
for
red phytochrome
tion, light, far-red light,
The
spores
of seedless vascular plants with
photosynthetic
surficial,
gametophytes
typically germinate in light (Raghavan, 1989), while those with
subterranean, nonphotosynthetic, mycorrhizal gametophytes
germinate
in the
dark The
(Whittier, 2005, 2006). germination of spores from
ferns of the
first
group, with one exception (Cooke
by
et 1993), stimulated red
al., is light
(Cooke
Raghavan, The
et al., 1987; 1989). effect of red light on spore
germination
in a species with underground, mycorrhizal gametophytes has
been tested on only one Ophioglossum
species, crotalophoroides Walter
The
(Whittier, 2006). germination which
of these spores, normally germinate
in the dark, inhibited by red
is light.
This study was
initiated to determine the inhibition of spore germination
if
by
red light occurs in another seedless vascular plant with subterranean,
nonphotosynthetic,
mycorrhizal
gametophytes. an broaden
In effort to the
study, spores from
a family other than the Ophioglossaceae were
selected.
Spores Lycopodium
of clavatum
a species with mycorrhizal gametophytes
L.,
(Bruchmann,
1910), were chosen because with time they undergo high
percentages
of germination
in culture
(Whittier, 1998).
Spores Lycopodium
of clavatum were
obtained from on Unaka
plants Mt.
in
Unicoi County,
Tennessee. Vouchers
on
are deposit the Vanderbilt
at
University Herbarium To
(VDB). reduce
the incidence
of
<
The
Table 1. effect of daily 3 Ominexposur,.stored, lr-red, and whit light on spore germination
ft 3
Lycopodium
in clavatum.
Spor
germinal
e
Percent
Treatment Yes No
germination
mW/cm
2
The
)
.
spores were wetted and stored in water for 24 hr before surface sterilization.
They were then surface sterilized with 20% Clorox (1.1% sodium hypochlo-
min by method Under
rite) for 2 the of Whittier (1964). sterile conditions, the
spores were rinsed with water, collected on paper, suspended in water
filter
mm
and sown on 12 ml of nutrient medium in culture tubes (20 x 125 mm)
with screw caps were tightened reduce moisture
that to loss.
medium mg MgS0 mg mg
The nutrient contained 50 -7H 0, 20 CaCl 70
4
2 2
,
NH N0
K HP0 mg
medium
and 150 per The was completed with
2
liter.
2 4 4 3 g
,
ml minor element and and
of glucose, 0.4 of a solution (Whittier Steeves, 1960)
FeEDTA medium
ml The was
4 of a solution (Sheat et al, 1959). solidified
pH
with 1.0% agar and was at 5.7 before autoclaving. The spores and young
gametophytes were cultured 23±1°C.
at
Spores were considered germinated once the spore coat ruptured and the
proximal cell (near the triradiate ridge) bulged out. The presence of rhizoids
cannot be used an indicator of germination because they form on
as later
multicellular gametophytes. In each case, 1000 or more spores were examined
These were
determine the percentages of germination. data (Table
to 1)
G
independence and
analyzed using the of (Sokal Rohlf, 1995).
test
had
The three experiments carried out in this study the following light
Red was obtained with monochromatic red (No. 650,
light filters
.
Supply Spiess and Krouk and white
Co.) as in (1977)
Jiological
mW/cm
2
The used was was
lamps. irradiance 1.0 Far-red light
.
obtained with transmitting plexiglass (FRF700, Westlake
a far-red filter
and Cundiff (1975) and incandescent lamps. This
Plastics Co.) as in Pratt
cm
light was passed through a Pyrex water cell (10 in depth) to reduce infrared
mW/cm
2
and supply an irradiance of White from
radiation to 1.0 light
.
mW/cm 2
The
fluorescent lamps had an irradiance of 1.0 irradiances were
.
measured with YSI Model 65 Radiometer (Yellow Springs Instruments).
a
min min
Except as otherwise noted, 30 of red light, 30 of far-red light, 30 min
AMERICAN FERN VOLUME NUMBER
196 JOURNAL:
98 4 (2008)
of white were given and white
light daily for the red, far-red, light treatments.
The
red/far-red or far-red/red treatments involved a total light exposure of
min
1 hr/day. In addition to the 30 white light treatment described above, a
2
12 hr per day fluorescent white light control raW/cm was included with
(0.3
)
each
of the three experiments.
Results
Two
preliminary experiments with short durations were conducted
to
determine was
demonstrate on
if it feasible to a red light effect spore
germination clavatum. Red white and
in L. light, light a far-red/red treatment
inhibited germination in these experiments. Spores in the dark, far-red light
and
a red/far-red treatment germinated. Because the germination percentages
were low with the dark and far-red treatments, another third and
final
experiment was with
carried out a duration of 110 days.
The
results of this third experiment are given in Table As found in the
1.
previous experiments red and had on
light far-red light different effects spore
germination in L. clavatum. Red light, like white light, inhibited germination
and
large percentages of germination occurred with and
far-red light darkness.
When
given in sequence red light reversed the effect of far-red light and far-red
light reversed the effect of red Far-red illumination
light. resulted in
germination same
at essentially the percentage as spores in the dark. In
addition to the results given in Table was found that spores exposed
1, it to a
mW/cm
2
12 hr/day white
light control (0.3 failed to germinate. Except
for
)
differences in the magnitudes of germination the were same
results the
for all
three experiments.
As
with Ophioglossum
crotalophoroides
(Whittier, 2006), the photorever-
sible germination response of Lycopodium clavatum spores red and
to far-red
light indicates the involvement of phytochrome (Toole, 1973). The active form
of phytochrome, induced by
Pfr, red light inhibits spore germination both
in
These show
species. phytochrome
results that an important component
is in
the germination of spores from clavatum, with
L. as those of
it is
Ophioglossum.
The min
30 red or white treatments reduced
light greatly spore germination
in L. clavatum, but did not eliminate as the 20 min exposures did
it for
Ophioglossum
(Whittier, 2006). Exposing the spores clavatum
of L. to a 12 hr
photoperiod
white
of prevented
light their germination. This the
raises
an
possibility that exposure to red light longer than 30 min necessary
to
is
eliminate spore germination
clavatum.
in
L.
The
and
effects of red on
far-red light the spores of clavatum
are essentially
L.
same
the on
as those the spores of O. crotalophoroides and on
opposite those fern
spores from species with
photosynthetic gametophytes. Germination promot-
is
ed by which
forms
Pfr, after the exposure to red light in species with
photosynthetic gametophytes (Cooke 1987; Raghavan, but
et 1989),
al., is
it
inhibited in the species tested with subterranean, nonphotosynthetic, mycor-
rhizal gametophytes (Whittier, 2006). Spore germination not promoted by
is far-
red light in fern species with photosynthetic gametophytes but occurs in these
it
two
species with subterranean, mycorrhizal gametophytes.
The
photoinhibition of seed germination insures germination underground
which would
rather than at the soil surface improve the possibility of
sufficient moisture for seedling growth (Salisbury and Ross, 1991). Photo-
Lycopodium and Ophioglossum would
inhibition of spore germination also
insure subterranean germination with improved chances adequate
for soil
moisture and for enhancing the possibility that young gametophytes will be in
A
the proximity of mycorrhizal fungi. close association between germinating
and young
spores mycorrhizal fungi important because gametophytes of
is
Lycopodium and Ophioglossum stop growing after a few cells unless colonized
by mycorrhizal (Bruchmann, Campbell,
fungi 1910; 1911).
White
light inhibits spore germination in seedless vascular plant species
with subterranean, nonphotosynthetic, mycorrhizal gametophytes (Whittier,
and The
1981, 1998, 2005; Whittier Braggins, 1994). photoinhibition of spore
now
germination in O. crotalophoroides (Whittier, 2006) and clavatum
L. is
known
to involve Pfr. Because the inhibition of germination by Pfr occurs in
two unrelated seedless vascular plant species with subterranean, mycorrhizal
may phenomenon
gametophytes, appears that be a general in this plant
it it
group.
Literature Cited
Keimung Sporen und Entwicklung
Bruchmann, H. 1910. Die der die
Lycopodium clavatum annotinum und selago Flora 101:220-267.
L., L. L., L. L.
Campbell, D. H. 1911. The eusporangiate. Carnegie Inst. Publ. Wash. No. 140.
The
Cooke, H. Racusen, G. Hickok and T. R. Warne. 1987. photocontrol of spo
T. R. L.
J.,
germination the fern Ceratopteris richardii. Plant Cell Physiol. 28:753-759.
in
Cooke, T. G. Hickok, W. Vanderwoude, A. Banks and R. Scott. 1993. Photobiologic
L.
I.
J.
J., J.
characterization of a spore germination mutant dkgl with reversed photoregulation in
t]
Photochem. Photobiol. 57:1032-1041.
fern Ceratopteris richardii.
Pratt, H. and C. Cundiff. 1975. Spectral characterization of high-molecular-weig
L. S.
phytochrome. Photochem. Photobiol. 21:91-97.
Cambridge
Raghavan, V. 1989. Developmental biology of fern gametophytes. University Pre;
Cambridge, U.K.
th Wadsworth
and W. Ross. 1992. Plant physiology, 4 Ed., Publishing Ci
Sai.isiu kv. F. B. C.
V
Sheat, D. E. G., B. H. Fletcher and H. E. Street. 1959. Studies on the growth of excised roots.
AMERICAN FERN VOLUME
198 JOURNAL:
9
W
rd
and
Sokal, R. R. F. Rohlf. 1995. Biometry. 3 Ed.
J.
Bot Gaz. (Crawfordsville) 138:428-433.
.
The
1973. effects of light, temperature and their interactions on the germination of
!eed Technol. 1:339-396.
Sci.
P. 1964. The effect of sucrose on apogamy in Cyrtomium falcatum. Amer. Fern
J.
D 1981. Spore germination and young gametophyte development Botrychium and
of
.
Jossum in axenic culture. Amer. Fern 71:13-19.
J.
3 1998. Germination of spores of the Lycopodiaceae in axenic culture. Amer. Fern
.
J.
113.
C. Pintaud and E. Braggins. 2005. The gametophyte of Lycopodium
J.
Red
ttier, D. P. 2006. light inhibition of spore germination Ophioglossum
in crotalophoroides.
Canad. 84:1156-1158.
Bot.
J.
and
ttier, D. P. E. Braggins. 1994. Spore germination in the Psilotaceae. Canad. Bot.
J.
J.
The
Steeves. 1960. u
apii;_ininv u
,. >!