Plants Have Slow Sex in Space

By Perrin Ireland | March 25, 2013 1:11 pm

A new study on plant reproduction finds that developing cells are very affected by altered states of gravity—a finding that has implications for our hopes for a future human society in space.

In order for plants to have sex, a pollen grain first lands on a stigma (the female part of a flowering plant.) Following a chemical come-hither signal from the stigma, the pollen grain grows a pollen tube, a tunnel for sperm cells to travel down to reach the egg for fertilization. Pollen tubes are the fastest growing cells in the plant kingdom. The pollen tube was used as a model system for a recent study on the effects of altered gravity on plant reproduction because a response in the pollen tube takes a matter of mere seconds.

Plants have the ability to sense gravity. There are specialized parts of some cells called statoliths, which occur, for instance, in plant root cells, which need to know which direction to travel—in this case, down into the ground. The cell senses gravity, and changes its behavior accordingly.

Pollen tubes don’t have statoliths and they don’t sense gravity. A pollen tube is on a mission to find and germinate an egg; if it were primarily concerned with responding gravity, that mission would be thwarted. The pollen tube grows in the direction of the egg, and it takes its cues from the egg’s chemical signals. This means that any impact of gravity on a pollen tube is due to the actual effects of gravitational force on weight-bearing loads in nature.

Much research has been done on the root-growing prospects of plants in space. But researchers wanted to understand the effect that altered states of gravity would have on a plant cell that doesn’t have statoliths. They exposed pollen tubes to two states of gravity: the first was 20 times the gravity of earth, the second, a stimulation of the lack of gravity in space.

What they found is that plants in microgravity grew smaller pollen tubes: their diameters were 8 percent smaller than those grown at Earth gravity. At five times Earth’s gravity, the tubes were 8 percent wider, and at 20 times Earth’s gravity, they were 38 percent wider.

This is because the assembly of cell walls was disrupted in microgravity, leading to a reduced growth rate. As a result, the germination rates were much lower in the lesser-gravity states, the researchers reported in PLoS ONE.

The findings are important for all kinds of reproduction in space. Cells’ internal transport is important in humans as well, particularly in the development of long neurons. If neurons can’t form properly, will we be able to grow babies of our kind with working brains in space one day? If plants can’t properly reproduce in altered gravity, will we be able to pull off agriculture in space?

CATEGORIZED UNDER: Living World, Top Posts
MORE ABOUT: botany, plants
  • Lance Gritton

    It would be interesting to see how centripetal gravity generation effects these findings. Will spinning a flower at 1g overcome these effects.

  • Andrew Osmond

    Of course one doesn’t need to worry about pollen tubes and germination if growing plants by cuttings, clones, and other vegetative methods

  • Randy Shelly

    This is probably a good argument for artificial gravity where we want to have a self-sustaining environment, including food production.

    I am taking a look at what it would take to create a space habitat that could accommodate up to 500 people ( This would be a two-stage effort, with a factory/facilities-based habitat (Space Habitat Alpha) being built first. Alpha would be a stand-alone space station with lunar-equivalent artificial gravity, capable of supporting up to 50 people, with its elements built on the ground. Alpha would then be used to build the larger Space Habitat Beta, using material from the Moon or, more likely, from asteroids.

    I’ve done a quick guestimate of the cost for the Alpha module, based on scaling-up Bigelow’s, BEAM and BA330 modules. For a linear scale up the cost is about $30B. Normally, estimating the cost of a larger unit, based on a smaller one, we can use a square-root law; but, anticipating some technical challenges, I decided to use a linear law.

    Compared with the ISS, (International Space Station), $30B is a good deal, and the Alpha Habitat would be more versatile. It would also make it possible to perform the highly automated work for the Beta Habitat in space, at a much lower cost than if it were manufactured on the ground.

    Contact me at if you have any comments or questions, or visit the Design Overview page at

  • Hypatia Hypatia

    We have a very nice home right here on Earth, often called the “Goldilocks Planet” because everything seems tailored for our version of life. (or is it the other way ).

    So, while adventures in space are fun and challenging for some, most of us would benefit more by cleaning up the mess we have made so far, and regulating population in our own best interests.


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About Perrin Ireland

Perrin Ireland is a visual science storyteller. She is a lifelong doodler, a learner who needs to visualize scientific concepts in order to understand them. She is Senior Science Communications Specialist at the Natural Resources Defense Council, where she helps creatively tell the stories of the science that underlies NRDC's work.


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