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How Plants Respond to Drought
| Article
# : |
18845 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
12 / 1991 |
2,348 Words |
| Author
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Elizabeth Chajes
Elizabeth Chajes is a media and information specialist in
marine communications at the College of Marine Studies,
University of Delaware. |
The telltale sings of a thirsty plant--drooping leaves and flaccid stems--send us rushing with a watering can to relieve the plant's misery. But a plant begins to suffer the effects of dehydration long before our eyes can detect any signs of need. Prominent among these effects are the cessation of cell growth, the impairment of photosynthesis, and frequently an inability to reproduce. Watering the plant will usually return these processes to normal, but sometimes depending on the timing, severity, and duration of the dry spell, the plant sustains permanent damage.
John S. Boyer, E.I. du Pont professor of marine biochemistry and biophysics at the University of Delaware's College of Marine Studies, is looking into these hidden effects of dehydration on plants. His state-of-the-art laboratory is located at the Marine Studies Complex in Lewes, Delaware, where he says good facilities, enthusiastic colleagues, and the nearby ocean combine to form an ideal work environment.
Land plants, Boyer points out, use water quite inefficiently. Most of the water absorbed by the roots evaporates through tiny pores in the leaves called stomata. Only a small fraction of the water goes towards the normal growth and maintenance of the plant. Even during a drought, plants absorb at least 10 times the amount they need to live.
"Corn, for example, uses 1.5 liters of water per day," Boyer says, "During a drought, this may be reduced to 200 to 300 milliliters per day, about one-eighth the normal. But growth and metabolism require only about 3 to 5 milliliters per day. We know this by measuring the amount of water the plant needs to reach full size, that is, the amount of water we provide minus the water lost by evaporation."
Boyer suggests that land plants have evolved recently and might not have had enough time to develop a fine-tuned response to dehydration. Perhaps in a few million years plants will be able to withstand dehydrating conditions much better than they do now. By contrast, plants have existed in the marine environment for a much longer time period and have solved their water problem relatively efficiently.
Marine plants are generally immersed, but they may still suffer dehydration. Although the protoplasm in marine plant cells is usually more concentrated than the surrounding seawater, under certain conditions higher-than-normal concentrations of salts in seawater tend to draw water out of the cells, and they become dehydrated
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