SUBJECT: Phytochrome and seed germination
DATE: 3/95
At The University of Calgary we have been doing an experiment for
a number of years with light sensitive lettuce seeds and their
germination under the influence of red and far red light (the
phytochrome pigment response in photomorphogenesis). This year
the seed lots were not very sensitive. I have two questions?
Does anyone know of a reliable source for the light sensitive
variety of lettuce for this experiment? Does any know of another
plant seed that exhibits a similar photomorphogenetic response?
Any information will be appreciated.
cheers
chuck curry
Chuck,
When all else fails with Grand Rapids lettuce try hydrating the seed in
the dark, give them a shot of far-red light then dry them down again for
class use. Not strictly kosher but it does give reliable results.
Best wishes,
John Hoddinott,
University of Alberta.
Charles,
I had a similar problem with the same experiment in my plant physiology
class this semester. We are using the Grand Rapids cultivar of lettuce,
the
standard variety used in most experiments in the literature. Our first attempt
found that the seeds germinated at a fairly high frequency no matter the
treatment. I went back to the literature and found that others have seen
lot-to-lot variability in the light response for seed germination and that
temperature can overshadow the light response. Temperatures below 25 C can
promote some germination in the dark. You may want to try the 25-28 C range.
However, temperature did not account for everything. The other problem we
had
was with our light setup. We had to better isolate our far red light source
from stray light and cut back some on the light intensity. With a few trials,
we finally optimized the setup and obtained some very nice data. I hope
this
was helpful.
Brad Goodner
Asst. Professor of Biology
University of Richmond
P.S. You may want to try seed lots from different companies as well.
Try Harris seed company....Should you find a new source that is light
sensitive and has low dark germination, always store the seed in a sealed
container in a freezor.....Light sensitive seed that have a high dark
germination may be made light sensitive by always using FR light as the
first
light exposure followed by R or FR.....For best light response always
imbibe seeds for 1.5 hours in the dark before light treatment....
Grand Rapids variety is more difficult to obtain these days as most
suppliers are treating the seeds so they will germinate in the dark....
Good luck... If you find a source of Grand Rapids that has not been
pretreated to germinate in the dark, please send address of supplier.
Cheers......
Jon Monroe <FAC_JMONROE@VAX1.ACS.JMU.EDU>
Charles Curry and Group: As Brad Goodner stated, Grand Rapids lettuce is
a
good choice of seed to use for such experiments and you will find lot-to-lot
variability. Part of the problem with these exeriments is that bulk
phytochrome in those seeds is made up of many different phytochrome's.
These are a family of pigments, that have overlapping functions. The
environment that seed is stored in, and the age of the seed, may change
the
amount of phytochrome, and the ratio of each kind of phytochrome. Because
some plant responses occur in far-red light, and some in red light, it is
important for the germination experiments to have clean red and far-red
light. You should use a light bulb (incandescent) for the far-red. Use a
red filter over fluorescent for the red light. A better approach would be
red and far-red light emitting diodes (but that is rather expensive).
Photon flux is important, if you can feel the heat of the lamp, then there
is a lot of far-red. Too many photons may mess up the experiment. Dim
light, and short exposure,for both red and far-red treatments is best for
the experiment. And the dark control has to be very dark. Remember to keep
your treatment short, long exposure to light may result in a High Energy
Type response (this HIR is not limited to seedlings), and recall that HIR
is
most sensitive (responsive) to far-red or blue, thus you may not "turn
off"
germination with long exposures to far-red. About other plant species,
check out Frankland and Taylorson (1983), and you might look into
peppergrass (Lepidium virginianum) and Kentucky bluegrass (Poa pratensis).
But remember, temperature can alter light responses in these grasses and
in
lettuce germination. Higher temp generally results in a more profound light
response. Hope this is of help., Dan
Dr. Dan Tennessen
Cornell University email: djt6@cornell.edu
F.O.H. CENET: dan_tennessen@cce.cornell.edu
47 Plant Sciences Bldg. Phone: 607-255-1799
Ithaca, NY 14853 Fax: 607-255-9998
I routinely use Agway 'Salad Bowl' lettuce and have never had
a failure. I use Carolina Biological filters mounted in a
simple 1"x4" wood frame. The red frame sits about 40 cm below
two
18" fluorescent tubes. The far-red frame sits about 30 cm
below a 40 W incandescent lamp. For dark we wrap in aluminum
foil and place under the FR petri dish in the FR frame. I
keep them under continuous illumination. I always get about
90% germination in white and red light, about 25% in dark and
0% in far-red in the first two-three days. The students count
and remove; they put all dishes in white light for 2-3 more
days. In general all ungerminated seeds then sprout; the
exception?...I never get quite to 90% in the far-red pre-treatment.
It is typically around 70%. Maybe this is an HIR response?
ross
@----------------ooOO---v__//--OOoo-------------------------@
| Ross Koning Internet: Koning@ecsuc.ctstateu.edu |
| Biology Department Phone: (203)-465-5327 |
| Eastern CT State University Fax: (203)-465-5213 |
| Willimantic, CT 06226 USA "physiologists have phun" |
@--------------------ooOO--OOoo-----------------------------@
Biolab Home Page