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
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.nethttp://koning.ecsu.ctstateu.edu
> ----------
> 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 readers.
> Further discussion of the reading is welcome. The paper provides answers
> 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 wild
> has
> been debated by botanists, without resolution, for almost a hundred
> years. Most of the controversy has focused on a single population of
> 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 167
> 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 in
> diameter at breast height. Most of these secondary trunks originated
> from
> root-like "basal chichi," that are produced at the base of trees that
> have
> experienced damage from soil erosion or other factors. No Ginkgos less
> than 5 cm in basal diameter were found in the mature forests of Tian
> Mu
> Shan.
>>>> Further discussion topics might include:
>> What should be call the fruit-like thing that falls from a "female" tree?
> A megaspore? a seed? It can't be a fruit and isn't really a seed if it has
> yet to be fertilized. The surrounding flesh produces butyric acid which
> is
> the source of the odor of rancid butter and romano cheese. Does butter
> still go rancid? (would our students understand this statment taken from
> Raven et al? Now I know why I prefer parmesan.)
>> How is it possible that fertilization takes place after the megaspore has
> 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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