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Re: Gib vs Auxin #2

Hello again Rob,

I greatly admire your scientific curiosity.  It is that sort of creativity
and imaginative associations that once in a while lead to great
discoveries.  However, here are my impressions on your last thoughts.  I'm
afraid that this time I have several reservations.

>     The reason I asked is because I have willow seed that I seem well
>and widely advised is quite hopeless. 

Willow seeds ripen and disperse in the spring.  They are extremely
short-lived and should be sown immediately after harvest. They have no
dormancy and germinate almost immediately after falling to the ground. Dirr
and Heuser (1987, the Reference Manual of Woody Plant propagation) speak of
a maximum storage period of 4 to 6 weeks, with germination rates dropping
fast after 10 days at room temperature. So I guess your sources are
probably right, unfortunately.

If you want to propagate a willow, why not just take cuttings?  They
virtually root by themselves and will give you much more reliable results.

>While it is reckless, I'm sure, to
>generalize all of Salix the genus, I am reminded of the weeping willow,
>and I've recently heard repitition of information in an old issue of
>Organic Gardening, about how water in which willow cuttings had been
>rooted would root virtually anything, due to a substance they called
>"rhizocaine", which sounds much lke an auxin. I had wondered if auxin
>might be leaching into the ground where the branches touch and possibly
>promoting the germination or longevity of the seeds. 

I have also heard somewhere that "Willow water" contains certain rooting
enhancers, although I have never heard of the term "rhizocaine".  A quick
leafing through the books I have on-hand did not give me any extra
information, unfortunately. My guess is that there are probably auxins
involved, like you suggested.

However, since auxin is not in any way related to the metabolism of seed
germination, dormancy or longevity, I sincerely doubt that willow branches
touching the ground could send out anything to affect the seeds around
them.  Please don't confuse rooting of cuttings with seed germination...
rooting cuttings generally involves creating NEW adventitious roots on a
severed organ (although in the case of willow, it is the expansion of
pre-formed root initials at the stem nodes).  Germination involves breaking
of dormancy (if any), water absorption, and rapid growth of an EXISTING
embryo.  The radicle is already present inside the seed.

>     While tending another project, Salvia pisidica, (I'm told outdoor
>treatment is required and I accept this) I was looking at some molecules
>which I think are related to the synthetic pathways for gibberellins,
>and I saw some that looked as if they might have functions of
>gibberellins and auxins on a single molecule.

I would be very curious to hear you expand on this.  What molecules are you
referring to?  Auxin and Gibberellin synthesis are very different
biochemical pathways (out of mercy to all, I will not expand on this).
They are not even synthesized in the same parts of the plant (auxin = in
shoot tips, while gibberelins are much less localized). What makes you
think the substances you refer to might have functions of both gibberellins
and auxins?  Their "apparent" chemical structure or recorded observations?

>     Does anyone have comments on this, or know of literature referring
>to this? Perhaps the significance is "biological economy", but I seem
>much confused by it in general.

There is a good amount of basic information on plant growth regulators on
the WWW. Any basic plant physiology manual also has a chapter on the topic
(consult your local library). Any search using the keywords "plant growth
regulators" or "plant hormones" will do.  You might be interested in the
following Web page address, which I have found to be an good (though
succinct) summary on plant hormones.  There's even a nice graph explaining
the role of Gibberelic acid on germination of cereals (but then you'll also
notice that gibberellin is involved only BEFORE the seed actually germinates):

<http://hortwww-2.ag.ohio-state.edu./hvp/TMI/HORT300/hormone.htm>

I hope this was of some help, and not too boring to all.

Have a great weekend everybody!

Denise

********************************************************
Denise Tousignant, M.Sc., Conseillere scientifique
Pepiniere forestiere de St-Modeste, 
410 rue Principale, St-Modeste, Quebec GOL 3W0 Canada
tel.: 418-862-5511  FAX: 418-862-0564
********************************************************
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