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hardy  Aroids)" <ARISAEMA-L at NIC.SURFNET.NL> Aroids)" <ARISAEMA-L at NIC.SURFNET.NL>
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From: Georgio Pozzi <studio.pozzitaubert at TISCALI.IT>
Subject: Re: Emailing: dormancy
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Il giorno 12/gen/06, alle 19:02, Massimo Meregalli ha scritto:

>  Hi everybody!
>
>  the problem of dormancy in tuberous plants has been studied in
> various scientific papers. Unfortunately, and perhaps obviously, most
> of these papers dealed with potato tubers. Of course, things can be
> very different in Araceae. However, dormancy is generally induced, and
> interrupted, by the levels of some plants "hormones", such as
> gibberellines, auxines, etc. On a pure evolutionary thought, the onset
> of a kind of triggering mechanism based on the concentration of a
> molecule inside the plant tissue seems to be quite favourable in the
> case of the tubers, which cannot be stimulated by daylength, and may
> have also a difficulty in being triggered by temperature, if they are
> deep enough. Interruption of dormancy can thus be determined by
> changes in concentration and or balance of various plant hormones. In
> case that these changes are determined by the activity of some
> enzymes, only initial concentration and rate of decay or modification
> can be responsible for the onset of the new vegetation, rendering thus
> the tubers relatively independent from the climate or daylength. The
> system may have evolved so that the tubers sleep long enough to pass
> winter in cold areas. This could also explain the different times of
> emercency in tubers of the same species grown in the same condition.
>
>
Well,  nearly the whole world follows alternate cycles of activity and
rest, double is the purpose: pass over worse conditions in the best
manner and restore " factors" lost during the activity, rest is however
always life with work by tuber cells.

Pregnancy ends with a hormonal "storm" to induce uterine contractions,
but statitics say we have  more births in humans during less-light
hours (rest period); on the contrary African herbivores have developed
a natural "timer" to get most deliveries all at the same time and
during light-hours (activity).

Hormonal and enzymatic levels ( and many other chemicals ) into a tuber
surely vary by themselves on a timer developed by that species for its
best, but, certainly, they  are affected by external conditions as the
moisture of the soil, temperature, pH and levels of other chemical
compounds ( some always present and some coming from the new compost
produced during last winter season and washed down into the soil by
rain) and, at last, time elapsed ( in cold conditions) from the
beginning of dormancy.

Note that in nature to obtain an effect we usually need two balanced
forces:  the first acts to induce the effect and the second, opposite,
is regulating, like a brake, that effect.

So, in Spring moisture usually increases, the same for temperature,
thus changing the complex chemical status of the tuber cells, beginning
from the external semipermeable membrane, and chemicals, old and new,
interact with the actual compounds inside the tuber.

" ALL" theese factors at the same time interact and work to induce the
plant to wake up.

Which are however those we can influence?

Easy with water and temperature, rather difficult to know what happens
in the soil in Spring, but we could increase natural  compost level
spreading it over the tuber, while watering, and this is what gardeners
do while "forcing" their flowers in greehouses ( after the beginnig of
growth the plants needs good light conditions too) ; impossible for the
present knowledge, to change internal "timer" and chemistry.


Giorgio
North Italy
zone6/7



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Il giorno 12/gen/06, alle 19:02, Massimo Meregalli ha scritto:


<excerpt> Hi everybody!


the problem of dormancy in tuberous plants has been studied in
various scientific papers. Unfortunately, and perhaps obviously, most
of these papers dealed with potato tubers. Of course, things can be
very different in Araceae. However, dormancy is generally induced, and
interrupted, by the levels of some plants "hormones", such as
gibberellines, auxines, etc. On a pure evolutionary thought, the onset
of a kind of triggering mechanism based on the concentration of a
molecule inside the plant tissue seems to be quite favourable in the
case of the tubers, which cannot be stimulated by daylength, and may
have also a difficulty in being triggered by temperature, if they are
deep enough. Interruption of dormancy can thus be determined by
changes in concentration and or balance of various plant hormones. In
case that these changes are determined by the activity of some
enzymes, only initial concentration and rate of decay or modification
can be responsible for the onset of the new vegetation, rendering thus
the tubers relatively independent from the climate or daylength. The
system may have evolved so that the tubers sleep long enough to pass
winter in cold areas. This could also explain the different times of
emercency in tubers of the same species grown in the same condition.



</excerpt>Well,  nearly the whole world follows alternate cycles of
activity and rest, double is the purpose: pass over worse conditions
in the best manner and restore " factors" lost during the activity,
rest is however always life with work by tuber cells.


Pregnancy ends with a hormonal "storm" to induce uterine contractions,
but statitics say we have  more births in humans during less-light
hours (rest period); on the contrary African herbivores have developed
a natural "timer" to get most deliveries all at the same time and
during light-hours (activity).


Hormonal and enzymatic levels ( and <bold>many</bold> other chemicals
) into a tuber  surely vary by themselves on a timer developed by that
species for its best, but, certainly, they  are affected by external
conditions as the moisture of the soil, temperature, pH and levels of
other chemical compounds ( some always present and some coming from
the new compost produced during last winter season and washed down
into the soil by rain) and, at last, time elapsed ( in cold
conditions) from the beginning of dormancy.


Note that in nature to obtain an effect we usually need two balanced
forces:  the first acts to induce the effect and the second, opposite,
is regulating, like a brake, that effect.


So, in Spring moisture usually increases, the same for temperature,
thus changing the complex chemical status of the tuber cells,
beginning from the external semipermeable membrane, and chemicals, old
and new, interact with the actual compounds inside the tuber.


" ALL" theese factors at the same time interact and work to induce the
plant to wake up.


Which are however those we can influence?


Easy with water and temperature, rather difficult to know what happens
in the soil in Spring, but we could increase natural  compost level
spreading it over the tuber, while watering, and this is what
gardeners do while "forcing" their flowers in greehouses ( after the
beginnig of growth the plants needs good light conditions too) ;
impossible for the present knowledge, to change internal "timer" and
chemistry.



Giorgio

North Italy

zone6/7




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