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I Don't Like Spam 08-06-2003 06:20 PM

reproductive biology of orchids question
 
OK... so I'll take the risk of showing my ignorance here. It's been
over 20 years since college, but this question came to mind when I
couldn't sleep the other night.

Orchids produce very large numbers of very small seeds. Is each seed
the result of an individual pollination/fertilization event?

Does the one pollen grain, one ovule, one seed rule apply? Do
"multiple maternal twins", for the lack of a better term, occur in the
plant kingdom? (I believe reduction of seeds occurs, but does
multiplication occur as well?)

With the simplicity of orchid seeds, is it possible that more seeds
are produced than pollen grains involved?

Is this a biological rule that is occationally broken, but you never
hear about it in Botany class? If so, what other plants reproduce in
this manner?

It would seem that the number of pollen tubes necessary to result in
the massive number of seeds produced would destroy the integrity of
the stigma, style, and ovary.

Also, when orchids are pollinated, can more than one pollinia be
involved? Does the presence of one pollinia (pollinium?) exclude
further pollinia? How many pollen grains can be contained in an orchid
pollinium?

This may differ from species to species, but does anyone know?

Can similar trends be found in other plants that produce pollinia,
such as milkweeds? What other plants produce pollinia?

Again, I claim ignorance in this matter... but also express curiosity.
Amazing the things that will bounce around in the brain when you
cannot sleep.

MMMavocado 08-06-2003 07:56 PM

reproductive biology of orchids question
 
Yes, as far as I know, each seed is genetically unique, from one ovule and one
pollen grain. But the big difference in Orchidaceae (Asclepiadaceae also does
it) is that they put their pollen into a lump called a pollenium, which is
carried by the bee/wasp/other pollinator as a single unit, so one pollination
event involves many thousands of pollen grains.

Iris Cohen 09-06-2003 03:08 AM

reproductive biology of orchids question
 
Orchids produce very large numbers of very small seeds. Is each seed the
result of an individual pollination/fertilization event?

Theoretically, yes. While there are orchids which are apomictic (reproduce
wuthout being pollinated) and even cleistogamous (self fertilize in a closed
bud), the above is normally true.

Does the one pollen grain, one ovule, one seed rule apply?

Yes, as far as I know.

With the simplicity of orchid seeds, is it possible that more seeds are
produced than pollen grains involved?

Anything is possible, but as far as I know, it is not a normal occurrence.

It would seem that the number of pollen tubes necessary to result in the
massive number of seeds produced would destroy the integrity of the stigma,
style, and ovary.

There isn't any style in an orchid flower. The ovary & other necessary parts
grow to accommodate the pollen tubes.

Also, when orchids are pollinated, can more than one pollinium be involved?


Possibly, but I assume the excess pollen would be lost.

How many pollen grains can be contained in an orchid pollinium?

Don't know, but it is a pretty large number.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)


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