David W. Kramer kramer.8 at OSU.EDU
Wed Sep 9 09:21:16 EST 1998

Russ Goddard wrote (in part):

Does anyone out there
>have any suggestions about what we could include in a lab on symbiosis?
>Does anything work particularly well for you?

In our Plant Biology 102 Introductory Plant Biology course (second quarter
of a two-quarter course for non majors) the students do an experiment with
soybean/Rhizobium symbiosis.  We grow inoculated and uninoculated soybeans
in high nitrogen/low nitrogen soil.  (The experiment uses minimal
greenhouse space because each team of two students sets up four 4-inch pots
with two soybeans each:  H+, H-, L+, L-.) At the end of approximately 7
weeks we terminate the experiment and assay for shoot weight, number of
nodules, and nodule weight (size).  As you know, soybean will not form the
association with Rhizobium in high nitrogen soils.  The experimental
results consistently confirm this.  However, we do not see major
differences in the shoots (qualitative or quantitative) because in this
early developmental phase (first 7 weeks) the plants are producing
relatively little protein (i.e., require less nitrogen) compared with the
amount they will be producing during seed maturation.  Unfortunately we do
not have enough time in the quarter to run the experiment to that stage of
development.  Nevertheless, the experiment is easy for our non-majors to
understand and it generates a lot of discussion about symbiosis, feedback
mechanisms, etc.... not to mention a discussion of the need for ag research
(a hidden agenda!) at our Ohio Agricultural Research and Development Center
operated by OSU at Wooster, OH.  By the way, the students also cut open a
nodule to see the pink interior.  This is leghemoglobin which binds O2 to
create an anaerobic environment for the Rhizobium.  This ties into our
discussion of aerobic and anaerobic cellular respiration.

If you would like a copy of the exercise, I could fax or mail it to you.

Dr. David W. Kramer
Department of Evolution, Ecology,
        and Organismal Biology
Ohio State University at Mansfield
1680 University Drive
Mansfield, OH  44906-1547
(419) 755-4344  FAX:  (419) 755-4367
e-mail:  kramer.8 at

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