QUESTION

David Hershey dh321 at excite.com
Mon Jul 12 20:59:17 EST 1999


For essential elements, such as calcium, there is often luxury
consumption, or the plant absorbs more than the minimum required for
optimal growth without it becoming toxic. Given that calcium cannot be
remobilized after it has been deposited in the plant, even if the new
growth becomes calcium deficient, the excess calcium might be considered
waste. Even below luxury consumption, there is very little unbound
calcium in the plant (the Ca - calmodulin story). In aroids, such as
dumbcane, there are large amounts of calcium oxalate, which may serve as
defense against herbivores, so perhaps there is a function for even
excess or "waste" calcium?

For mobile nutrients, such as nitrate, where the excess is stored in
vacuoles, any luxury consumption might better be considered a storage
reserve because it can be remobilized for later use. 

David Hershey
dh321 at excite.com

James W. Perry wrote:

> 
> Well, I waited until now to stick my neck out, but it has been my
> understanding
> that at least certain "waste products" become compartmentalized in the
> vacuole(s). From Esau, Plant Anatomy...
> 
> "In contrast to animals, which normally eliminate excess inorganic material to
> the exterior, plants deposit such materials almost entirely in their tissues.
> The inorganic deposits in plants consist mostly of calcium salts and of
> anhydrides of silica."
> 
> While most of these substances are localized in the vacuoles as crystals,
> there
> are reports of cytoplasmic structures as well (or maybe better termed
> 'hyaloplasmic' structures).
> 
> Is an "excess inorganic" substance a waste product? Sure seems to be that it
> could fit the definition.
> 
> jim
> 
> James. W. Perry, CEO/Campus Dean
> Professor, Department of Biological Sciences
> University of Wisconsin - Fox Valley
> 1478 Midway Road, P.O. Box 8002
> Menasha, Wisconsin 54952-9002
> Office: 920.832.2610
> FAX: 920.832.2674
> jperry at uwc.edu



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