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Effects on Cell Wall Development
Name: Sheena
Status: student
Grade: 9-12
Location: TX
Country: N/A
Date: 1/4/2005
Question:
Hi, i'm doing a science project about the affects of
relaxants and stimulants on a soybean plant's height and its cell walls.
I am using sugar, tobacco, caffeine, and aspirin all with water on 25
different plants. The height was affected greatly but I have looked
through a microscope and still cannot tell a difference in the cell walls
of the plants. Another problem is that the aspirin and caffeine plants
did not grow at all so i couldn't even take a sample of them to look at
under the microscope. Do you know if the cell walls are affected at all
in my project?
Replies:
Would recommend recording the before and after sizes or incremental growth
measurements of the plants, and comparing the measurements with a chart and
simple statistics (averages, etc.) Perhaps not possible to view any changes
in the cell walls with a light microscope since either no change in the
wall's thickness or would need an electron microscope. Possibly could look
at the size of the plant cells instead.
Anthony Brach PhD.
To begin with, I would urge you to repeat the experiment and control all
variables you can think of. Be certain that your treatments are the
only conceivable differences between the groups of plants. The fact
that your caffeine- and aspirin-treated plants did not grow at all makes
me suspect that you need to perform more repetitions of the experiment.
Based on my knowledge of plant growth hormones, I would expect sugar to
have no direct effect on cell walls. However, it will be a good food
source for bacteria and fungi and thus it will tend to make the plants
susceptible to bacterial and fungal diseases.
Tobacco is very toxic stuff in general. Tobacco leaves contain dozens
of different toxins, many of which could affect your plants in ways that
are very difficult to predict.
Aspirin (acetylsalicylic acid) is chemically similar to the well-known
plant hormone salicylic acid. To my knowledge, salicylic acid is not
involved in growth; it is generally involved in responses to stress or
injury and it triggers thermogenesis (heat production) in some plants.
Aspirin is somewhat acidic, though, and acidic solutions can cause plant
cell elongation by "loosening" the cell walls. However, this effect is
only seen when the acidic solution is applied directly to the cell
walls.
Caffeine is chemically similar to the well-known plant growth hormone
indole acetic acid (IAA, also known as "auxin"). IAA is very clearly
involved in plant growth - in particular in the growth of stem and root
cells. I don't know if caffeine might have a similar effect, but it
seems conceivable to me. IAA seems to work by stimulating the cells to
pump acid into their cell walls, thereby making them "looser" or more
"stretchy". This mechanism is debatable, though.
I very much doubt that you will be able to see any cell wall structural
differences with a microscope. If there are growth differences, you
would be more likely to see them in terms of internode length.
I would also caution you against making any connection between these
effects and the effects seen in animals due to these substances. In
animals, these stimulants affect the nervous system; plants don't have
nervous systems and the mechanisms by which plant hormones work are very
different from the mechanisms seen in animals. Plant physiology is
quite different from animal physiology.
Christopher Perkins
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