QUESTION

Stefanie Galgon smg4 at DANA.UCC.NAU.EDU
Mon Jul 12 14:40:15 EST 1999


	Oooh... now we have tangented to the topic of secondary plant
metabolites!  I love this stuff.  Nobody has mentioned glandular
trichomes!!! Trichomes are epidermal outgrowths that can be found on all
plant organs.  They vary in size and complexity, and include hairs,
scales, and other structures.  Secondary metabolites are classified into
three main groups: phenolics, nitrogen containing compounds (e.g.
alkaloids), and terpenes. Secondary compounds (some toxic to animals, some
inhibit seed germination -- the allelopathy David brought up), tend to be
biosynthesized and localized in secretory structures at the surface of a
plant (primarily on the leaves).  The foremost secretory organs of plants
in some families are glandular trichomes (may I be so bold as to make that
statement?), which are found on the abaxial and adaxial surface of the
leaves, varying greatly in structure between and within species (you'll
see many descriptions... capitate stalked and sessile, peltate).  
	GT's have a unicellular or multicellular head composed of
secretory cells, usually sitting on top of a stalk of nonglandular cells.
Essentially, capitate glandular trichomes consist of a unicellular or
multicellular stalk and a unicellular or bicellular head.  Peltate consist
of a basal cell located within the epidermis and a single stalk cell
subtending a head composed of encapsulated secretory cells.  My point is,
the subcuticular cavity of mature peltate glandular trichomes house
accumulated monoterpenes and other compounds (biosynthesized within the
plastids of the secretory cells, and transported to the subcuticular
cavity).  If something munches on the leaves, the capsule ruptures and the
compounds are released.  Let us say a deer decides to munch on some
Dugaldia... if the quantity of a particular toxic monoterpene is high
enough within the GT's, that deer will become ill.  Various plants in the
Lamiaceae family have been investigated for toxic and deterrent effects
against insects.  Extracts from Dracocephalum moldavica, Lavendula
angustifolia, Salvia plebilia, and S. sclarea  have shown toxic effects on
the cotton aphid (McIndoo 1983), from Hyptis suavelobens had toxic effects
on Lipaphis erysimi when tested on cabbage leaf (Roy and Pande 1991), and
from Elsholtzia iriostachya retarded insect growth, including pupal
formation and adult emergence (Bhattacharya and Bordolsi 1986).  The
leaves of some Artemisia species house compounds that inhibit seed
germination of other plants (but not their own!).  The leaves are dropped,
the compounds leech into the soil....

Boy, I sure am rambling here, aren't I?  Did I just steer wayyyy off the
subject at hand?  Anyone else?

Steffi


******************************************************************
Stefanie Galgon			lab/message: (520) 523-7735
Department of Biology		
Northern Arizona University	smg4 at dana.ucc.nau.edu

"Life is a banquet, and most poor suckers are starving to death"  
Auntie Mame
******************************************************************

On Sat, 10 Jul 1999, David Hershey wrote:
 
> If plants do produce organic compounds that are toxic, either as
> unintended byproducts or as allelochemicals (those used to inhibit
> growth of other plants) they may store them in vacuoles where they will
> not cause damage. Besides shedding of plant parts, woody species could
> possibly store waste materials in old, nonfunctional xylem although I do
> not know if there has been research on that.
> 
> David Hershey
> dh321 at excite.com
> 
> Bill Williams wrote:
> > 
> > I would love to hear a definitive answer to this question; my
> > introductory-biology students ask similar questions frequently.  Here's my
> > answer:
> > 
> > Toxic metabolic products arise because the food that organisms consume
> > doesn't precisely match the organisms' needs.  Urea is an excellent
> > example:  heterotrophs necessarily consume complete organisms, or at least
> > complete cells, but the ratio of calories to nitrogen *in* organisms is
> > much, much lower than the ratio of calories to nitrogen *needed* in food.
> > Thus, they have a constant excess-nitrogen problem and excrete urea (or
> > uric acid, or ammonia, or some other nitrogenous waste).  But the world of
> > autotrophs is completely different:  they obtain energy from the sun (which
> > creates is own problems and gives rise to numerous metabolic pathways for
> > dissipating excess energy) and materials from the air and soil solution.
> > In general, such organisms simply don't take in materials that they don't
> > need, or at least that they cannot use without poisoning themselves.
> > 
> > So:  if you don't want to bother with kidneys and livers, don't eat!
> > 
> > -W2
> > 
> > At 08:54 -0700 7/9/99, Santosh Baburao Mane wrote:
> > > I am pharmacy student , we study about plants ,and use of plant as
> > >sources of drugs
> > >
> > > So my question is," why plants are able to survive with out excretory
> > >system that is  kidney or liver
> > >like organs ???" They do not need detoxification ?? why metabolic products
> > >are not able to give toxicity
> > >to plant and why they induced toxicity to animal cells only .
> > >  plants cells having any mechanism  for detoxification or is it
> > >natural???
> > >
> > >So pl help me to finding out answer  of this
> > >
> > >
> > >pl mail me ans.
> > >
> > >Thanks
> > >Santosh
> > >San_dha at giaspna.vsnl.net.in
> > 
> > ________________________
> > William E. Williams
> > Biology Department
> > Saint Mary's College of Maryland
> > 18952 E. Fisher Rd.
> > Saint Mary's City, MD  20686-3001
> > (301)862-0365
> > 
> > Summer:  Botany  Department
> >          Aven Nelson Building
> >          University of Wyoming
> >          PO Box 3165
> >          Laramie, WY 82071-3165
> >          (307)766-6293
> 
> 




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