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Name: Jothi
Status: other
Grade: other
Location: Outside U.S.
Country: India
Date: Summer 2011

How does a plant manage without an excretory system ? Some plants are known to live for a hundred or more years. During their life sapn, they, doubtless, intake a lot of unwanted stuff ? How do they get rid of it ? Not possibly through transpiration, as unwanted salts cannot be excreted that way. Please explain.

Plants take up a variety of unusable compounds including toxins. These are sequestered within plant tissues.

For example, Sincerely,

Anthony R. Brach, PhD Missouri Botanical Garden / Harvard University Herbaria

Dear Jothi,

If you think of plants (autotrophs) the same way you think of humans and animals (heterotrophs), your question is very appropriate. If all your energy and nutrients came from eating other plants and animals, you would need to take the good nutrients with the bad toxins and find a way to remove the toxins. Plants produce all of their chemical energy from light and can produce all of their nutrients from inorganic minerals and carbon dioxide. So the level of toxins taken up by the plant will be much less than for animals. Nevertheless, toxins are taken up by plants (herbicides are great examples of how we use the property to human advantage) and they have enzymes that can alter some toxins so that they can be excreted through the roots or by deposition at the leaf margins with removal by the next rainfall. Often times toxins are sequestered in the vacuoles of plant cells, which are often considered to be less biologically active than the rest of the cell. The toxins can be lost if they remain in parts of the plant that are discarded annually such as leaves or bark.

--Jim Tokuhisa

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