University of Montreal researchers found that changes in
gravity affect the reproductive process in plants. Gravity modulates traffic on
the intracellular "highways" that ensure the growth and functionality
of the male reproductive organ in plants, the pollen tube.
"Just like during human reproduction, the sperm cells
in plants are delivered to the egg by a cylindrical tool. Unlike the delivery
tool in animals, the device used during plant sex consists of a single cell,
and only two sperm cells are discharged during each delivery event,"
explained Professor Anja Geitmann of the university's Department of biology.
"Our findings offer new insight into how life evolved
on Earth and are significant with regards to human health, as a traffic jam on
these highways that also exist in human cells can cause cancer and illnesses
such as Alzheimer's."
How gravity affects
The interior of animal and plant cells is like a city, with
factories—called organelles—dedicated to manufacturing, energy production and
A network of intracellular "highways" enables the
communication between these factories and the delivery of cargo between them
and between the inside of the cell and its external environment. Plant cells
have a particularly busy highway system.
"Researchers already knew that humans, animals and
plants have evolved in response to Earth's gravity, and that they are able to
sense it," Geitmann explained.
"What we are still discovering is how the processes
occurring within the cells of the human and plant bodies are affected by the
more intense gravity, or hypergravity, that would be found on a large planet,
or the microgravity that resembles the conditions on a space craft.
Intracellular transport processes are particularly sensitive to disturbance,
with dramatic consequences for cell functioning. How these processes are
affected by a change in gravity is poorly understood."
The cells were placed
into a large centrifuge, along with a camera attached to a microscope, enabling
the researchers to track in real time how the cells develop in the intense
gravity generated by the centrifuge. "Thanks to the facilities at the
European Space Agency, I was able to determine how hypergravity and simulated
microgravity affect the intracellular trafficking in the rapidly growing pollen
tube," explained Dr. Youssef Chebli, a researcher in Geitmann's lab.
"We chose pollen, the carrier of the male sperm cells,
as our model because of its pivotal role in plant reproduction and agriculture
and because of its extraordinarily rapid growth, meaning that we could observe
the effects of the hypergravity within seconds."
How the research was
The researchers stained specific structures within the
cells, which revealed how the cellular components move around and how the
cellular transport logistics responds to the changing gravity environment.
"We found that intracellular traffic flow is compromised under
hyper-gravity conditions and that both hyper and microgravity affect the
precisely coordinated construction of the cellular envelope in the growing
cell," Chebli said.
"This allows us
not only to understand general principles of the reproductive mechanism in
plants but, more importantly, how the intracellular transport machinery in
eukaryotic cells responds to altered gravity conditions. Our findings have
implications for human health as similar effects are likely to occur in human
cells such as neurons where long distance intracellular transport is