Pollen tubes are go!

Kat - At the University of Montreal in Canada, Professor Anja Geitmann is developing models to explain how tiny tubes grow out of pollen grains to fertilise flowers under different conditions, such as zero gravity - her work has featured in the media with headlines such as "sex in space!" and worse. Naked Scientist Simon Bishop spoke to her to find out what she's actually up to.

Anja -  We try to understand how plants function.  Plants consists of cells just like the human body does.  Only that the difference between the cells of a plant and that of a human is that the cells are surrounded by a wall and this wall consists, for example, of cellulose microfibrils.  So, this is the stuff your clothes are also made from.  And so, in order for such a cell to grow, it has to deform its cellulose material.  In order to form a particular shape, it has to regulate the material properties, just like a balloon that blows up and becomes a sphere or becomes something more interesting.  The plant cell that we work with is a very, very long tube.  It's a catheter-like delivery tool of the sperm cells that serves to bring the sperm cells from the pollen grains to the ovules where the egg cells are housed in the flower.  And so, in order to understand how this tube is formed, we do all kinds of stuff to it.  We use inhibitors, we use enzymes, but the fun stuff we do is when we put it in the centrifuge and expose it to altered gravity conditions.

Simon -  So, what do you find out by putting a plant cell, a pollen tube into first a microscope and then put it inside a centrifuge?

Anja -  So, the centrifuge had the purpose to increase gravity, the effect of gravity.  What we found is that all kinds of processes that are necessary in the cell to allow it to grow are affected.  So, in the cell, things have to be transported from one end of the cell to the other.  That is the same process that occurs for example in neurons, the cells of the human brain.  This transfer process was affected strongly by gravity either by hypergravity or by microgravity - so, the absence of gravity.  What we found is that as a result of this, growth was compromised and cell shape was altered.  And from that, we can conclude that intracellular processes, although they occur at a micron scale are affected by mechanical influences such as increased gravity or lack of gravity.

Simon -  So obviously, plants in natural conditions wouldn't experience extreme gravitational forces, but what you're doing is testing this to the limit so you can understand the forces that are normally involved in building a pollen tube.

Anja -  So, the pollen tube is a crucial step in reproduction of plants that delivers the sperm cells.  Without pollen tube growth, we won't have fruit, we won't have the next generation of plants.  This process is easily affected by all kinds of influences.  And so, we can imagine that effect such as microgravity or hypergravity -  microgravity would be the case on the international space station or any other space travelling vessel, or hypergravity on a planet bigger than ours would affect plant growth.  And so, we simply try to understand how plants function and use this as a tool - altered gravity as a tool to affect cellular functioning from a mechanical point of view.

Simon -  And where next?

Anja -  Okay, so the pollen tube is the cell that has very simple geometry.  It's long and cylindrical.  But what we really want to understand is how much more complex shapes are formed.  So for example, if you look at the surface of a leaf, it has most intricate cellular shapes and we would like to understand how these complex shapes are formed and how they become to be functional during the development of a plant embryo into an adult plant.

Simon -  Any plans to put other leaves and other plants into centrifuges?

Anja -  That will be fun - putting an entire plant into a centrifuge.  What has been done of course is that we have grown plants in space.  That means microgravity conditions and plant functioning is affected by this process.  It's very difficult to actually pull apart what is the effect of the absence of gravity and what is the effect for example of the absence of convection.  Convection is the absence of air movement that is a result of the absence of gravity.  And so, there's a whole lot of challenges that are out there for us.

Kat - That was Anja Geitmann from the University of Montreal. And now it's time for a roundup of this month's genetics news.