Video transcript: Modelling leaf shape

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March 2012

Lead author Samantha Fox from the John Innes Centre on Norwich Research Park
Leafs come in all shapes and sizes you only have to look around your garden or the local parks to see lots of different shapes from maple to beech to sunflower leaves but how do these leafs form, how do they turn from a bud of a few cells to this complex shape.

Video shows various leaves shapes (throughout video also)

So to find out how something works you might want to re-create trying to make it and in this case we've used conversation modelling to re-create a growing leaf virtually.

Video shows scientists working in the lab

So we used a novel kind of imaging so we can visual the cells dividing and expanding and we can use a mathematical model to simulate the growing leaf and try and understand what the recipe was and how was it made and by combining these we have actually come up with some simple rules which underlie leaf growth because even though we see all these different shapes of leafs actually there aren't lots of different complicated ways in which they form we have founded that plants have an inbuilt system for detecting orientation like a built in compass but instead of using a magnetic field they have a molecular pattern which they produce themselves with reference points like the base and tip...

Video shows Samantha pointing to the various parts of the leaf

...instead of north and south on a compass and once you realise that it's possible to generate lots of different shapes based on this simple system.

So this molecular pattern is fixed at a really early stage of development when a bud starts to divide and turn into a new leaf the patterns already present from an early stage.

Video shows buds on a tree

Part of the pattern is to transform this dome shaped bud into the flattened leaf shape that we see on the mature plant. How does that happen?

Video shows computer simulation of a leaf growing into a dome shape

If this dome shape grew equally in all directions we would just have a giant dome we wouldn't have a leaf at all it wouldn't be flat, it wouldn't have a pointy tip so what happens that actually there is a molecular pattern and most of the growth comes from the base of the leaf...

Video shows computer simulation of a leaf growing naturally into a mature leaf shape

...and from the base of this very early bud and that's the pattern which is fixed early in development so we are interested in finding out how organs develop actually we haven't used laurel to work on as it would be pretty difficult it's a really big plant it is a huge tree and we wouldn't be able to fit that under a microscope we've used Arabidopsis which is a model species and it is a relative of lots of important crop plans like Brassicaceae or seed rape. We've used a confocal microscope to be able to grow the seedlings around the Brassicaceae under the microscope and actually film it during growth...

Video shows continuous stills of the bud growing at microscopic level

...and capture all the cell divisions and cell expansions that are happening and what we have done is taken the imagining data that we've got, made lots of measurements of how the leaf is growing over time but to try and understand how leafs are growing we've used convensational modelling, that is creating a virtual leaf. You could animate a leaf, you could draw a leaf on your computer but to actually make a leaf grow dynamically from a young bud and recreate the shape of the leaf realistically what we see in biology is much more difficult. We have been able to learn a lot from the imagines we have collected and by testing different models we have been able to understand what the rules are for what you would need to make a leaf.

So this is an example of one of our models.

Video shows Samantha holding up a blue 3-D model of a leaf with red spots on it

Actually a 3D print out of a virtual leaf so we can see we have captured the leaf shape, it has a narrow region here in the petiole becomes wider in the lamina and narrower up towards the tip so leafs don't normally look like this with these funny red spots on but actually we use this to help us visualise where the growth is coming from. We mark spots at the very early stage where it is just a small bud and as the model grows we can visualise where the growth is coming from.

Video shows computer simulation of the growth of the model leaf

We would like to extend the model to take account of more leaf shapes like maple leafs which have finger shape leafs or even much more complex shape leafs like this tomato compound leaf which actually this is the whole leaf and is built up by these smaller leaflets. This is a major breakthrough in our understanding of plant growth. The more we understand about how plants grow the better we can prepare for our future for providing food, fuel and preserving diversity.

Generation of leaf shape through early patterns of growth and tissue polarity - Kuchen, Fox et al Science (2012)

For more information see http://rico-coen.jic.ac.uk

JIC Communications 2012-05-30

Sponsored by John Innes Centre & BBSRC