plant excretion

Ross Koning koning at ECSUC.CTSTATEU.EDU
Wed Jul 14 18:50:24 EST 1999


At 11:58 AM -0400 7/14/99, Jon Greenberg wrote:
>So, am I still the only one on this list who thinks that plants do have
>to contend with organic metabolic wastes?
>
>Jon Greenberg
>BSCS

No, but the question is quantity and type of waste.
Plant cells recycle very well and hold some toxic
wastes in vacuoles.  If you are an herb in an
herbivorous world, keeping in some poison is a good
idea. Plants produce a range of toxic (to animals)
compounds that we find deadly, useful, or down-right
fun depending on kind and dose. The toxins (to plants)
that cannot be metabolized are simply compartmentalized
to keep them away from critical biochemistry. In live
cells the vacuole or various "microbodies" in cells
are good places to store, process, etc. toxic wastes.
In whole plants, toxins are shed with each drop of
leaves in autumn (or whenever a particular "evergreen"
turns over its leaves). In saline environments, some
plants are excluders (not interesting for this point),
some are shedders (mentioned in previous sentence), and
some are secreters...salt glands are used to excrete
the uptaken toxins. Another example includes trees with
heartwood. Here toxins are transported and compartmented
in tyloses...cells that bulge into the now-dead-and-no-
longer-transporting secondary xylem. These tyloses are
invested with a range of compounds...many of which are
at least toxic to bacteria, fungi, and many invertebrates
(if not more!). These toxins typically include heavy-duty
polycyclic ring compounds with conjugated double-bonds
that allow the chemicals to have a color. In many cases
these tylose-laden xylem cells en-masse then, have a dark
color.  We make great furniture out of it.  The living
tylose cells generally die when sufficient toxin has been
stored there.  It is assumed that the cell is killed by
the toxin it stores... But are the compounds waste or
intentional anti-herbivore defense?

With all that said, it would be safe to also say that
what people have written about animals off-loading nitrogenous
wastes is true.  Plants don't do that very much as the
nitrogen is a precious input. The recycling methods for
nitrogenous compounds in plants are comprehensive.  Bambi
urinates in the woods...plants take in Bambi's waste gladly,
process it into useful amino acids, proteins, etc. and make
leaves, flowers, or fruits, for Bambi to eat.  Plants do
have mechanisms for detoxification from excess mineral
nutrition, but that happens so rarely in the real world
that it is almost "artifact biology" for the major nutrients
(yes, some minor nutrients-eg boron-become interesting in certain
kinds of soil, etc.). So in general, plants don't have nearly
as much toxic waste to handle...they make their own stuff
and recycle it primarily. Their primary "way of contending
with waste" is to recycle it very fast. They don't have to
urinate because they don't need to get rid of that much.

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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