The hunt for allelopathic plants

Ross Koning koning at ECSUC.CTSTATEU.EDU
Mon Sep 13 07:32:38 EST 1999


At 2:59 PM -0500 9/11/99, Beverly Brown wrote:
>Hello!
>
>I am setting up a lab from Vodopich and Moore.  We are going to test
>plants for allelopathic potential.  The technique is to grind up plants
>in a blender, put the slurry in a sterile petri dish and see if radish
>seeds will sprout or not.  The manual does not suggest any species to
>use.  Can anyone suggest potentially allelopathic species which I could
>locate in and around Rochester, NY?
>
>Thanks loads!
>
>Beverly

Hi Beverly!

Ailanthus has been suggested in the literature,
but the "seeds" (actually schizocarps) of many
Apiaceae have shown good inhibition of lettuce
seed germination and seedling growth.  Fennel
or Anise can simply be put in your petri dish
in a suitable amount of water (about 3 mL free
water after all imbibition has finished). The
major components of the oil of these species
will work too and at concentrations expected
from literature values in oil yields.  This makes
a well-documented assay in which the natural
material and its level of active ingredient
bring about similar levels of inhibtion.  I
usually remove the apiaceae seeds by hand and
sow the lettuce seeds in the remaining water
extract.  For a wild Apiaceae, you might try
wild carrot--though I haven't tried it to see
how well it may work...and I don't know what its
essential oils are either.  As to amount to use,
for Fennel you need about 400 seeds in a 10 cm
Petri dish, soaked about two days, to get a nice
effect. A dose response can be obtained easily
by a series 0, 25, 50, 100, 200, 400 seeds in
separate dishes. In addition to germination rate,
you can monitor radicle length and root hair
length. Depending on the species/active ingredient
you try, these two measurements can be strongly
affected. This is easiest with a reticule in a
dissection microscope. There is a bit on this on
my website including some graphs (a bit "funky"
with animation but "real" otherwise).

I think too that it is a bit more "real" to imagine
a lettuce seed finding itself landing in a stand of
fennel under a shower of its schizocarps. The chance
of a seed coming in contact with a slurry of plant
extract is comparatively "unnatural".

One other situation that my class diagnosed was
lettuce germination in tomato juice.  If seeds only
need moisture and reasonable temp to sprout, why
do they fail in tomato juice? Why do seeds inside
a nice warm and juicy tomato NOT sprout?  If you
simply use a canned tomato juice as your source, it
will definitely prevent lettuce seed germination
(again 5 mL per 10 cm Petri dish). The students can
then provide hypotheses to test. They will probably
get pH, osmolarity, and abscisic acid ideas. The
pH of the juice can be measured, and a parallel
germination series in buffers can be prepared to
show the pH sensitivity of lettuce seeds. You want
a wide range of pH buffers to see the complete spectrum...
a phosphate or phosphate/citrate series should be OK.
The group can measure the osmolarity of the tomato
juice (with an osmette using freezing point depression
or vapor pressure methods, etc.) and then run a parallel
series with various osmolarities of sorbitol, mannitol,
or others. Measuring the AbA content of tomato juice
is problematic, but a series of doses of AbA in parallel
with the tomato juice should allow one group to determine
what concentration of AbA might be expected in the tomato
juice if the technology were available in the classroom.
If memory serves, the osmolarity alone can explain the
the results observed.

ross

________________________________________________________________
Ross Koning                 | koning at ecsu.ctstateu.edu
Biology Department          | http://koning.ecsu.ctstateu.edu/
Eastern CT State University | phone: 860-465-5327
Willimantic, CT 06226 USA   | fax: 860-465-4479
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