"KONING,ROSS E. Biology
KONING at easternct.edu
Fri Dec 8 10:34:50 EST 2000
The seeds have two possible problems, one
that I just hinted at in my last post to the group...
hinted at because I'm not sure of it since I
don't have a producing female around here.
Someone who DOES could really help us all
out with these questions.
Based on my experience with cycads, I think
it is possible that a female ginkgo can produce
ovules that develop fully without being pollinated.
If that is true, then the "seeds" that one recovers
may actually be dead-end ovules. In areas where
females have little access to pollen, this could be
the majority of the "structures" that fall from the tree.
I'm suspecting that our literature on fertilization
happening on the ground may be based on finding
many "seeds" that are unpollinated ovules. The
productive ginkgos that I have had access to, years
ago, did seem to hold onto some ovules into the fall...
beyond leaf drop. It may well be that the dead-end
ovules are shed first and that the pollinated ovules
are held on the tree until after syngamy. That makes
sense physiologically, but of course is speculative
on my part. So, collecting drops from the tree may
not give you many germinations because you might
not be picking up seeds...depending on when you
collect. I'd love it if someone did a time course and
looked for what was falling when. It would be quite
excellent work if pollen tubes were stained for
observation in each ovule case to show at least the
potential for on-the-ground continued development.
Samples from each sampling date could be saved
and subjected to later observations to demonstrate
higher percentages of further development. Someone
having a productive female with an upwind male
could do this critical work.
Finding Ginkgo eggs on the ground is not good enough
evidence that syngamy occurs on the ground. I
always remind students that you cannot go by what
you think you see: most chicken eggs that you find
in any given town might lead one to believe that
syngamy occurs after the shell goes on somehow.
It's just that most of the eggs in town are from hens
that never saw a rooster in their life! And the few
"fertilized eggs" that you can find... probably in a
health food store...aren't really eggs at all. They
are zygotes or young embryos in a shell. I think
ginkgo may be a parallel that needs more elucidation.
The second problem, which is described in print
is an after-ripening process that ginkgo seeds (the
true seeds with an embryo) require. This involves
the degradation of the aril and also some not-quite-
frozen temperature to follow for several weeks. I'm
not sure if this is an abscisic acid breakdown period
or not...but typically the seeds need a stratification
and then vernalization before they will germinate.
I also understand that germination time is quite long
Ross E. Koning, PhD
Professor of Biology - Goddard Hall
Eastern Connecticut State University
Willimantic, CT 06226 USA
Pager: (860)-744-2705 (leave return number at beep)
Email: koning at easternct.edu
Home: koningr at snet.net
> From: jperry at uwc.edu
> Sent: Wednesday, December 6, 2000 2:27 PM
> To: KONING at easternct.edu
> Subject: RE: Ginkgo homework
> I've been picking up seeds for a while and seem to have trouble getting
> to germinate. Do they need to be stratified? (I would not think so.)
> -----Original Message-----
> From: KONING at easternct.edu
> To: plant-ed at hgmp.mrc.ac.uk
> Sent: 12/5/00 1:00 PM
> Subject: RE: Ginkgo homework
> Hi Scott,
> You asked a couple of questions about Ginkgo
> biology...here are some answers I hope...
> Indeed the aril of the ovule is the fleshy structure
> that produces the butyric acid smell. The smell
> is also a large component of rotten-milk...such as
> one finds when trying to use a days-old "empty"
> once-pasteurized-milk bottle. THAT smell...yes.
> As for what is inside the ovule, of course it has
> outer layers of integument and to the interior, the
> megasporangium (aka nucellus). These tissues
> are all diploid maternal-genotype tissues. Inside
> the nucellus, one diploid cell (the megasporocyte)
> divides by meiosis to produce megaspores. Typically
> four are produced but only one survives as the
> "functional" megaspore. This megaspore is haploid.
> It will produce a multicellular megagametophyte by
> mitotic divisions. This megagametophyte gets invested
> with much storage material (starch, oil, protein, etc.).
> This is the tissue that people eat when they munch
> on "Ginkgo nuts" (the quotes are because they are
> NOT NUTS AT ALL botanically). The closest familiar
> equivalent is the "pine nut" or pignoli that are used
> in various Mediterranean cuisines. You are eating
> mostly haploid megagametophyte! At one end of this
> megagametophyte is one (sometimes more) egg cell.
> This egg cell will join with a sperm cell to make a
> zygote that develops into a Ginkgo embryo...if all
> works out well in terms of sexual interaction.
> The sexual interactions include: pollination and
> syngamy. Pollination in Ginkgo occurs when the
> ovule is VERY young on the tree. The ovule is
> tiny, the megasporocyte may not have undergone
> meiosis yet! But the integument is present in full
> with a tiny opening, the micropyle, ready to catch
> the pollen grains from a male Ginkgo tree nearby.
> The pollen grain is trapped by a sticky droplet that
> appears at the micropyle and is pulled into the
> ovule between the integument and nucellus. Here
> the pollen tube will germinate and digest a pathway
> through the nucellus. This happens in the spring
> and early summer. That process on the tree is
> pollination...not to be confused with syngamy.
> By fall, meiosis is complete, the megagametophyte
> is fully developed, the ovule has EXPANDED with
> lots of good storage material inside the megagametophyte
> (the "nut"), and the integument has produced a fleshy
> outer layer, the aril. However, the pollen tube is still
> penetrating the nucellus.
> The ovule falls from the tree. The bruised fleshy integument
> layer (the aril) will start making butyric acid. The pollen
> tube finishes its pathway through the nucellus to the
> egg. The sperm cell swims through the last bit of digested
> fluid and the egg engulfs it. This is the SYNGAMY event.
> It happens while the ovule is on the ground in the fall.
> Some people are still using the word, fertilization, for
> this event...but we are not talking about mulch, compost,
> or miracle-grow here, or even egg or sperm counts...no
> syngamy is the better word for this union of gametes,
> the egg and sperm.
> The zygote develops into an embryo while the aril
> continues to degenerate. Ultimately the stony inner
> layer of the integument, a papery nucellus layer,
> the megagametophyte storage tissue, and the embryo
> constitute a mature seed. This will germinate in the
> spring under good conditions.
> I hope this helps.
> Ross E. Koning, PhD
> Professor of Biology - Goddard Hall
> Eastern Connecticut State University
> Willimantic, CT 06226 USA
> Pager: (860)-744-2705 (leave return number at beep)
> Office: (860)-465-5327
> Home: (860)-423-9724
> Email: koning at easternct.edu
> Home: koningr at snet.net
> > ----------
> > From: Scott_Shumway at acunix.wheatonma.edu
> > Sent: Tuesday, December 5, 2000 11:42 AM
> > To: plant-ed at hgmp.mrc.ac.uk
> > Subject: Ginkgo homework
> > I would like to assign the following homework for the listserv
> > Further discussion of the reading is welcome. The paper provides
> > to many of the questions being tossed about on the listserv.
> > Del Tredici, P; Ling, Hsieh; Yang, Guang. 1992. The Ginkgos of Tian Mu
> > Shan.
> > Conservation Biology vol. 6, no. 2, pp. 202-209
> > Abstract
> > The question of whether or not Ginkgo biloba still exists in the
> > has
> > been debated by botanists, without resolution, for almost a
> > years. Most of the controversy has focused on a single population
> > trees
> > located on Tian Mu Shan (Tian Mu Mountain) in Zhejiang Province,
> > China, a site of human activities for approximately 1500 years.
> > Regardless of its origin, the Tian Mu Shan Ginkgo populations is
> > biologically significant by virtue of its long survival in a
> > semi-natural state
> > under conditions of intense interspecific competition. A total of
> > Ginkgos were counted and measured in the 1018 ha Tian Mu Shan
> > Reserve. Many of the trees were growing on disturbance-generated
> > microsites, such as stream banks, steep rocky slopes, and the
> edges of
> > exposed cliffs. Forty percent of the censused individuals were
> > multitrunked, consisting of at least two trunks greater than 10 cm
> > diameter at breast height. Most of these secondary trunks
> > from
> > root-like "basal chichi," that are produced at the base of trees
> > have
> > experienced damage from soil erosion or other factors. No Ginkgos
> > than 5 cm in basal diameter were found in the mature forests of
> > Mu
> > Shan.
> > Further discussion topics might include:
> > What should be call the fruit-like thing that falls from a "female"
> > A megaspore? a seed? It can't be a fruit and isn't really a seed if it
> > yet to be fertilized. The surrounding flesh produces butyric acid
> > is
> > the source of the odor of rancid butter and romano cheese. Does
> > still go rancid? (would our students understand this statment taken
> > Raven et al? Now I know why I prefer parmesan.)
> > How is it possible that fertilization takes place after the megaspore
> > fallen from the tree?
> > Scott Shumway
> > Associate Professor of Biology
> > Dept. of Biology
> > Wheaton College
> > Norton, MA 02766
> > 508-286-3945
> > "Scott_Shumway at WheatonMa.edu"
> > fax 508-285-8278
> > ---
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