The Journey of the Pollen Tube: Food Security in a Changing Climate


When most people think of pollen, they
probably think of allergies and runny noses. While pollen may be the source of
our sneezes. It is also the source of our food. Pollen contains sperm,
which fertilizes plants, allowing them to reproduce. What ends up on our dinner plates begins when a pollen grain lands on a plant’s
stigma. Soon after, the pollen grain germinates
into a pollen tube, which is a true hero of our story. The pollen tube is an
incredible, single cell focused entirely on delivering to sperm cells to the
plant’s ovule. To arrive at the ovule, the pollen tube
undergoes tip growth, which is a form of unidirectional cell growth. This is a rather exceptional process,
considering that the cell can grow over a thousand times its original length in
just a few hours! In fact, pollen tubes are the fastest recording extending
cells. After the pollen tube has traveled the entire length of the plant’s
style, it arrives at the ovule, which contains the egg and central cell. Once
here, the pollen tube bursts and releases the two sperm cells, for a process called
double fertilization. One of the sperm fuses with the egg, creating the embryo
that will become the new plant. The other sperm fuses with the central cell, which
develops into the endosperm, a nutrient-rich tissue that supports the
development of the embryo. This is what we eventually will eat! Wheat endosperm
is ground into flour for bread, and the endosperm of corn are the kernels that
we eat directly off the cob. These products are global food staples,
and we depend heavily on them in order to feed our planet’s growing population.
As we’ve seen, the growth of the pollen tube transports the sperm to the plant’s
ovule, where fertilization occurs. Fertilization allows the plant, whether
it’s corn, wheat, or another crop to start growing. So, the success of the pollen tube’s
journey, from stigma to ovule, is essential for our food supply system. If
this cellular journey goes wrong, we cannot produce major crops such as corn,
rice, wheat, and tomatoes. The growth of the pollen tube is temperature-sensitive,
so climate change poses a great risk to our food supply. Out of all plant cells,
pollen tubes are the most temperature sensitive. In fact, a pollen tube that is
fully functional at a certain temperature might be unable to locate
the ovule at a temperature only a few degrees higher, resulting in a completely
sterile plant! For instance, experiments have shown that
the pollen tubes of corn and wheat grown at 30 degrees Celsius (86 degrees
Fahrenheit) were unable to successfully complete double fertilization. Climate
scientists predict that global temperatures may rise between 2 and
6 degrees Celsius by the year 2100. So in many places where corn and wheat
are grown, the “threshold temperature” of 30 degrees Celsius will likely be
crossed by the end of the century. This puts us at risk of losing some of our
staple foods. So what can we do to protect our food supply? One solution
would be to halt climate change by greatly reducing our admission of
greenhouse gases, such as carbon dioxide. However, at this point, climate change has progressed so far that it may not be possible to save our crops. Instead,
scientists are working to engineer thermotolerant crops To do this, more research needs to be
done to understand how each step of the pollen tube journey could be engineered
to be more heat-resistant. So the next time you sneeze, or eat a
piece of pizza, be sure to think about the mighty pollen tube, and the
scientists working hard to protect its incredible journey.

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