At 7:15 PM 2/7/96 -0800, Anne Heise wrote:
>I have a student who wants to know exactly what's happening as a potato
>expands. He also wants to know if a plant benefits at all when it makes
>a gall or any swelling due to infection by a microorganism. (In other
>words, it may be clear that the insect or pathogen benefits if the plant
>tissues enlarge, but would the plant be worse off if it didn't enlarge?)
I think growths/galls take energy from the original
plant that would otherwise be used for their own
development. So I see galls, etc. as parasitic...
but see at bottom for another idea.
On the other hand, a potato tuber provides a means
for vegetative propagation (cloning) that allows a
plant to expand and fill an area with its own stems
and leaves, and thus reduce inter-specific competition
for light, nutrients, etc. This would amplify the
number of flowers it has, making it a larger "target"
for pollinating insects to carry pollen away for
sexual reproduction and to bring pollen from distant
individuals for the same purpose. So I think the
tuber offers that reproductive advantage.
The tuber provides a means for a digging mammal (hog,
dog, etc.) to carry propagules ("eye" buds) away and
thereby serve as a disperser. This further adds to
the selective advantages. You now have two possible
dispersal vectors (seed and tuber).
Finally, physiologically, the underground tuber provides
a means for a potato to be a perennial in areas with
suitably mild weather. The lightest frost will wipe out
the above-ground stems, but the tuber can take considerable
frost and still send up new shoots next year. If you have
a garden with potatoes, you always have some volunteers
next year (even in Michigan!).
I haven't heard of any similar advantages for galls, however.
Besides nutrient diversion, leaf galls shade the adjacent
mesophyll, so I doubt there is much advantage. It might be
interesting to see, however, if the cytokinins induced by
gall formation would delay leaf senescence. Your student
could make some observations on oak leaf galls and note the
times of senescence for uninfected and infected leaves on the
same oak tree. This could be a very interesting study.
\ Ross Koning \
\ Biology Department \
\ Eastern CT State University \
\ Willimantic, CT 06226 USA \
\ Koning at ecsu.ctstateu.edu \
\ http://koning.ecsu.ctstateu.edu/default.html \
\ Phone: 860-465-5327 \
) Fax: 860-465-5213 )