HERB - Pollen and allergy

[Kathleen Keeler]

Greetings from Agnes
I'm trying to get this right and its not easy

Pollen, one of my text books says, is a collective term for pollen
grains.
Pollen grains are structures containing 2 or 3 cells, one of which will
divide
to become the sperm cell of the plant. Pollen goes from one plant
(acting as
male) to another plant (receiving as female) where on the stigma of the
flower
the sperm cell grows out of the pollen grain and grows as long tubes
until it gets
to the ovary down in the flower, were fertilization occurs and a new
embryo is
created.

A pollen grain contains all the stuff of a cell, protein, nucleic acid,
sugars, other carbohydrates...the lot. The pollen grain's outer wall
(exine)
has two functions--to resist drying, since drying out  will kill the
cells inside, and to
activate growth if the pollen grain falls in the right place (on the
stigma of
its own species).  The resisting drying makes pollen outer walls so hard
they last
millenia.  The activation proteins are apparently the ones that people
become
allergic to.  These proteins move out of the pollen grain and into the
surrounding
area. On the stigma, pollen tube development ensues.  In your nose,
these
chemicals are exposed to your immune system, which, in the case of
allergic
individuals, touches off the reaction.

While ragweed's pollen cell chemistry contains protein molecules
specific to
ragweed the pollen grain also has molecules shared with other ragweeds
and
with composites generally. Maybe only the ragweed proteins touches off
your
immune reaction, but in launching its response, you are likely to make
antibodies
to every possible surface in the invading cell.  That means you will
make antibodies
to composite family proteins, even tho they didn't start it.  And that
means that you
will be sensitive to those proteins if you run into them later--in any
context.

Arent' the tests done to tell what people are allergic to skin tests?
They rub a little cat
dander and ragweed pollen and maple pollen on your skin, and if a welt
appears,
allergy is identified?

So your immune system isn't fooled if a "known enemy" enters by a route
other than
the nose.

And the problem is the complex proteins in the pollen grain, not the
pollen grain's shape.

Shape helps it sail through the air.  Ragweed is a bad allergen and
sunflower isn't mainly
because ragweed is wind pollinated and blankets its surroundings in
pollen, hoping some
gets to the next flower.  Ragweed pollen stays in the air well and
there's LOTS of it.
Sunflowers stick their pollen on bees and butterflies and don't make as
much pollen and
certainly don't throw it around.  (But apparently both have shared shape
characteristics that
tell the expert: Asteraceae pollen.)

Still working on getting the details right.  Thanks for the chance to
think this through!   Point out
any discrepancies please.

Agnes
kkeeler1 at unl.edu


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