LIGHTING UP LEAVES

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Lighting up leaves




Video transcript

A little florescent dye illuminates a complex circulatory system beneath the leaf’s surface. But what drives the pattern of these veins?

This question has intrigued physicist Marcelo Magnasco for years.

‘I guess that simply because of the mysterious beauty of the patterns.’

This network provides structure, transports water and nutrients and does it in the face of bugs, fungus and other attackers.

‘The network is built to withstand life, right. Leaves have been strongly optimised over millions and millions of years to be, you know some of the most remarkably adapted organs that we can find in this planet.’

And to a mathematical physicist like Magnasco, this evolutionary adaptation can be understood with numbers. Assuming evolution has shaped the geometry of the network, you can think of this pattern as the optimal solution, the best answer to a puzzle that takes into account the job of the leaf and the challenges facing it.

Magnasco along with research fellow, ‘my name is Elena Katifori’, wanted to understand what problems this lemon leaf’s loopy pattern solves.

‘And then what we do is an insanely huge calculation in which we make many many random perturbations to the network. ‘

One perturbation to the network could be vein damage, and this is where their cool florescent demonstration comes in. Katifori shows the advantage of alternate pathways here.

‘Yep, so I punch the hole in the leaf which you can see here. In this little vial here I have the florescent dye and then as soon as I put this in you are going to slowly start seeing the dye travelling through the veins and you will see the trajectory of the dye.’

‘This, you know, pretty close to obvious that if you want your network to be resilient to damage you will want to have some loops, exactly how many and how big is the question we are addressing in our work.’

The calculation revealed that resilience isn’t the only advantage of this loopy structure.

‘If the demand at every single point where you’re distributing fluctuates’ – for instance the sunny side of the leaf may need water when the shady side doesn’t, that’s a fluctuation in demand – ‘if those fluctuations happen you achieve efficiency not by having lines dividing into lines but by having essentially circles dividing into little circles.’

So their calculations revealed that changes in demand and potential for damage make the circle-within-circle structure optimal and this is similar to the way the lemon leaf’s network looks. But it’s worth noting that not all plants have come up with this particular solution.

Take the ancient ginkgo.

‘It has survived for millions of years so it’s doing pretty well.’

And obviously designing optimal networks for transport isn’t a problem that only leaves space.

‘The question of how to deliver stuff has been posed since the times the aqueducts were built in Rome so this is a question that has been studied a lot in the context, not so much of the natural science but in the context of delivering goods.’

But perhaps even more seductive than the practical applications here, is just how cool it looks.

‘That’s the profound and interesting thing about elegance and beauty that they are not really devoid of utility and practicality, right. I mean have you seen a Ferrari? They become pretty by being highly optimised and so there’s a deep connection between beauty and utility that I personally don’t understand but I make use of it.’ 

Happy Valentine’s Day from Science Friday. I’m Flora Lichtman.