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.