Negative Phototropisms

Ross Koning koning at ECSUC.CTSTATEU.EDU
Wed Nov 5 08:47:48 EST 1997

At 12:31 PM -0500 11/4/97, Gary wrote:
>My problem is, yet again, the plants.  What plant(s) can grow quickly
>AND show negative phototropism?  Please help!!!


I suggest using roots.  Most roots are negatively phototropic.
The primary roots of large seed seedlings are easy to anchor,
manipulate, and observe.  Broad bean (Vicia faba) and kidney
bean (Phaseolus vulgaris) might be excellent choices.  In
working with roots, there is ONE very important factor to
take much care with...desiccation.  Roots are not covered with
a waxy layer of cutin, so they desiccate very quickly.  It is
important to do your work in a very humid chamber.  If the seed
were anchored in an opening in a plexiglas enclosure, and the
chamber was misted (as in aeroponics), this would be good.
The light could penetrate the plexiglas easily.  Having the
plant material enclosed, however, causes another factor to
become critical...temperature. You would want to monitor the
temperature inside the chamber and ensure that any heat from
your light source is adequately trapped by a heat filter (maybe
a water-filled tank made with a fish-bowl or similar container
between the source and the root chamber).  Luckily, phototropic
responses do not need high irradiances (in most cases), so the
light can be relatively dim and thereby cool.  You could use
a fluorescent source to reduce the heat generated.


Ross Koning                 | koning at
Biology Department          |
Eastern CT State University | phone: 860-465-5327
Willimantic, CT 06226 USA   | fax: 860-465-4479

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