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Rock doc: Living on a different clock

By
May 3, 2011 |

E. Kirsten Peters mug

Peters

It’s obvious that miners focus on the highest concentration of gold or copper they can find. And geologists like me are always on the lookout for unusually high concentrations of metals in veins and rocks. We go where the best stuff is, and make a living helping to bring it to where it’s used in everything from the lead and zinc in your car battery to gold crowns for your teeth.

I know the geological perspective about resources pretty well. But recently I had the chance to think about how some very different actors approach the question of the raw materials they need.

Our friends in the plant kingdom are masters of using some very low-concentration raw materials. They depend on the carbon dioxide in the air, which is present in the atmosphere in only trace amounts. They get water from thin films of moisture in the soil. And they absorb minerals that are present in low concentrations near their roots, sending out root branches and root hairs to increase what they can take in.

From the point of view of surviving with only scarce raw materials, plants are impressive. They start with diffuse ingredients and out of them they make good materials like carbohydrates, proteins and oils. That’s quite a trick, one highlighted in my mind recently when I heard a lecture from biologist Roger Hangarter of Indiana University.

And plants are actually impressive on several fronts.

As we all know, many plants will orient their leaves toward the sun. If you don’t rotate the flowerpot on your windowsill, the plant in it will “tip over” and grow in the direction of the sunlight. And towering sunflowers orient their leaves toward the east in the morning, overhead at midday, and toward the west in the evening.

Many plants take advantage of nightfall to sweep their leaves back toward the east so that they are ready for dawn. Not a bad trick for an organism that doesn’t have a brain or a compass.

Some plants, like beans, drop their leaves at night, then raise them back up in the morning. Charles Darwin wondered why that’s the case. He came up with the idea that frost-sensitive leaves could lose a lot of heat energy to the dark night sky if they were directly exposed to it all night long. To test his idea, he propped up some bean leaves but let others droop down toward the Earth. Sure enough, those held up and exposed to the dark night sky (against their will, so to speak) were more likely to freeze.

Beans also show there’s a circadian rhythm in some plants. Just as your body senses the 24-hour rhythm of the planet – at least it will if you don’t drink too much coffee – some plants have an internal clock. Beans drop their leaves roughly each 24 hours even if you keep them in a dark closet for a few days.

Energy from sunlight is converted in leaves in what’s called chloroplasts, or what I’d call microscopic green blobs. But too much light for chloroplasts can be a negative thing. I was blown away watching video made by Prof. Hangarter showing the green blobs move inside cells depending on how much sunlight strikes a leaf. In strong light, the chloroplasts line up behind each other along the edge of a cell, making a bit of shade for one another. In low light, they spread out along the cell’s floor and ceiling, soaking up all the rays they can.

In several different ways what Prof. Hangarter taught me is that plants move and adapt to events around them each day. But we humans don’t tend to think about their accomplishments because they move much more slowly than you and me.

With time-lapse photos it’s clear to even a rock-head like me that plants move all the time. Their rhythms are slower than those of the animal kingdom, but they move nonetheless, both in terms of microscopic little blobs sliding within cells and large leaves and stems orienting themselves toward sunlight or away from the dark night sky.

I’ve got a new respect for the vegetation around me – an appropriate turn of events in the springtime.

Dr. E. Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard. Follow her on the web at rockdoc.wsu.edu and on Twitter @RockDocWSU. This column is a service of the College of Agricultural, Human, and Natural Resource Sciences at Washington State University.

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