Thursday, June 25, 2009

Dune Builder





The photograph at the top of this post shows a cross section of the leaf of marram grass Ammophila arenaria, the grass that’s primarily responsible for trapping wind-blown sand and building the dune systems around our coast that are such important wildlife habitats (bottom photo). Marram grass survives in the arid environment of a sand dune by rolling up its leaves during long periods of drought, so that all the leaves’ breathing pores or stomata (see http://beyondthehumaneye.blogspot.com/search/label/stomata) are inside the rolled leaf, minimising water loss. This cross section of a partially rolled leaf has been stained with fluorescent dyes to light up different cell types within the leaf, with the outside surface of the leaf at the bottom of the picture (smooth, curved surface) and the inner convoluted surface at the top. The outer surface of the leaf at the bottom is composed of a layer of thick walled cells, covered with a thick cuticle to resist wind-blown sand abrasion and this layer also acts like a spring, giving the leaf a natural tendency to roll up under drought conditions. The stomata are hidden on the inner surface of the leaf amongst those stubbly hairs near the bottom of those convolutions – which in the whole leaf are actually ridges and furrows that run along the whole length of the leaf. The clusters of thin-walled blue cells at the base (i.e. in the ‘valleys’) of the furrows of the convolutions are responsible for unrolling the leaf – when it rains and the plant takes up water these thin walled cells inflate like balloons, forcing the leaf to unroll. Other features that you can see in this leaf cross section are the snaking rows of reddish cells which are actually the cells containing most of the chlorophyll, that carry out photosynthesis – in order to make the dyes fluoresce I had to irradiate this leaf section with blue-violet light, which paradoxically makes green chlorophyll fluoresce red. The other distinctive features are the scattered structures that look like ‘smiley faces’ with a pair of large ‘eyes’ with a blue open ‘mouth’ – these are the leaf veins that conduct water and sugars along the leaf – they’re the plant’s internal plumbing system.

16 comments:

  1. Even more fascinating information; I do enjoy your writing and photographs.

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  2. That top photo is just superb Phil. I have often idly unfurled marram leaves without really understanding the structure. What I'd like to know is how those 'blue' cells work. Is it just that they have thinner walls so can absorb or lose water faster than the adjacent ones?

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  3. One thing is for sure Phil. There would be no sand dunes round here without plants like the marram grass and the North Sea would be a lot closer to my village.

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  4. Hi Nyctalus, I think it's two things - thin, flexible walls that allow them to collapse and inflate and a build-up of sugars inside the cell, which draws in water by osmosis when water becomes available again.

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  5. It's a wonderfully useful grass John. Sometimes, when the sand dunes are eroded by unusually high tides, you can see the exposed fibrous root system, which is massive compared with the aerial parts of the plant.

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  6. do you know the cells (vascular bundles) have smiley faces? it looks like this smiley :D

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  7. Hello Tyng, inner cheerfulness in a plant?!

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  8. Thanks Disa, the fluorescent stains produce wonderful colours

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  9. I can't wait for someone to animate those "faces" to "sing" some song. "Happy to see you again" for instance.

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  10. Hi Phil,

    Just wanted to say hello. I work at Kew Gardens (head of horticulture and other bits and pieces) but also interested in plants generally as well as algae...(talkingplants.blogspot.com). I just tweeted on your wonderful picture of the grass leaf cross section.

    Also interested in making contact because I've just become a Visiting Professor at Durham University so it would be interesting to catch up some time.

    Tim Entwisle

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  11. Hi Phil
    I tweeted this photo earlier - I wonder if it would be possible to use it commercially... would be interested to hear from you on this if possible...

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  12. Hi David,

    Please would you e-mail me about this on p.j.gates@durham.ac.uk

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  13. fantastic !!!!
    Thank you for all the images that are a source of inspiration for creating my jewelry

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  14. Hi Jane, I'm delighted that the images are of use to you. Thank you for visiting. With all good wishes, Phil Gates

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