Answer 1:
Your question sent me off to the internet to
read the article. It’s really interesting because
we don’t usually think of plants as having a fast
response. I am not a botanist and didn’t know the
answer to your question, so I did what I usually
do to figure something out in biology. First, I
took a quick look at papers in science journals by
this author. He is really interested in how the
plant cells communicate with each other, so
the papers I saw did not mention the source of the
calcium.
Then I went back to thinking about what I know
about plants. Plants pull calcium out of the
soil. They use energy to pump calcium from
the soil into root cells. Then the plant needs a
way to get calcium up to the rest of the cells.
There are tiny tubes that run up the plant from
the roots. Plants don’t have hearts, so
how do they move things up against gravity?
They use the power of the sun to pull things up
from the roots. Here’s how it works:
First, the sun provides heat that causes water
to evaporate out of tiny holes in the leaves
(these are called stomata). Water has a lot
of amazing properties. One is that water molecules
stick to each other. Another is that water
molecules stick to other things, like the sides of
those tiny tubes. So when one water molecule
evaporates, it drags another one up behind it.
That one drags another one up, and it’s sort of
like a chain of water molecules, all
dragging up the molecules below. Calcium and
other nutrients get dragged along too.
So how does that help answer your question?
This whole evaporation thing (it’s called
evapotranspiration) takes time. To see how
long, try the old demonstration of cutting celery
off at the bottom and putting it in a cup of
colored water. Gilroy’s plants were moving
calcium very quickly because of an emergency. So
this is what I think happens, the calcium is being
delivered to most cells slowly through
evapotranspiration, so every cell has some. The
damage could happen anywhere. Once a group of
cells is damaged, a signal is sent to all the
nearby cells to send their calcium over in a
hurry.
Imagine that your cafeteria kept all the napkins
in one place and everyone would grab one and walk
to a table that may be far away. Suddenly, someone
spills their milk and everyone at the table
quickly hands over their napkin. After the spill,
everyone might get up and walk all the way to
where the napkins are. (Okay, maybe only one
person would go get the napkins, but you can see
what I mean.)
So why do you think the plant doesn’t just load up
EVERY cell with calcium?
Thanks for asking,
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