hydrotropism

Thomas Björkman tnb1 at cornell.edu
Thu Jan 25 20:48:30 EST 2001


Hideyuki Takahashi has done a lot of the work on hydrotropismn to bring the
subject back. He reviewed it in Journal of Plant Research. 110:163-169,
1997. The main challenge with studying it is that gravitropism is a much
stronger tropistic response. As a high school lab project, the technical
apects would be daunting, as would the necessary separation of the water
and gravity responses.

Hydrotropism is an important phenomenon for people growing plants in
microgravity (i.e. in spacecraft). Without gravitropism, the roots do tend
to follow other cues. Takahashi describes this in a recent publication (J.
Plant Resarch 112:497-505, 1999)

It is also important to realize that the angle of root gravitropism changes
with the moisture level. In dry conditions, roots grow straight down, but
as it gets wetter, the roots shift to a wider angle. If the soil is
saturated, they will grow horizontally or up. High school students can
actually demonstate this easily with corn seedlings. Germinate the corn to
a centimeter or two of radicle. Then mount it so the root is a centimeter
or so over water. Keep the humidity around the whole thing high enough that
the root doesn't shrivel (ca 90% RH is good).  The root will grow down to
the water, then turn and grow up a few mm. Then it goes down again. I've
made it go back and forth several times. I got the design from a woodblock
print in an old (19th century) textbook that was reproduced in Joe Ycas' MS
thesis. (Jonathan--you might remember him from Bradfield hall). If only I
could remember the book!

Thomas Björkman

Jon Greenberg wrote:

> Hello again, plant folks.
>
> I am editing a high school biology lab manual that is under revision,
> and came across an activity to demonstrate hydrotropism. I recall
> learning in grad school about 20 years ago that roots grow toward water.
> However, I understand that this has been questioned and some do not
> agree that there is such a thing as hydrotropism.
>
> Can anyone enlighten me on this point/
>
> ---






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