Speculation: 8 Hormone System is Now Possible
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the lines of previous discussion. All the hormones would be made in
great amounts by meristematic cell and small amounts by mature cells:
When a meristematic cell makes or takes in more than enough sugar to
support both itself and any cell dependent on it for sugar, such that
growth is possible it makes Auxin.
When a meristematic cell makes or takes in less than enough sugar to
support both it any cell dependent on it for sugar, thus the plant
must rely on stores and cannibalizing of older tissue it makes
GIbberellin in order to continue growth of the meristematic cells.
When a meristematic cell makes or takes in more than enough Oxygen and
Carbon Dioxide to support both it any dependent cell in growth, it
makes Brassinosteroid.
When a meristematic cell makes or takes in less than enough Oxygen and
Carbon Dioxide to support growth it makes Ethylene.
When a meristematic cell has growth levels of water it makes Salicylic
Acid.
When a meristematic cell has senescent levels of water it makes
Abscisic Acid.
When a meristematic cell has growth levels of minerals it makes
Cytokinin.
When a meristematic cell has senescent levels of minerals it makes
Hormone X (Jasmonic Acid? Polyamines?).
Cells do not divide unless they have growth levels of sugar, gases,
water and minerals. This is not indicated to the plant except by high
enough levels of all four growth hormones Cytokinin, Salicylic Acid,
Brassinosteroid and Auxin.
A (perhaps non-meristimatic cell) does not senesce unless it has
senescent levels of sugar, gases, water and mineral. This is
indicated to the plant cell by high enough levels of Gibberellin,
Ethylene, Abscisic Acid and Hormone X).
The growth hormones are usually higher during the day, the senescent
hormones are usually higher during the night.
Senescent hormones not only stop growth they induce alternate ways of
getting the nutrients. One way this is done is by inducing a higher
yielding but more risky way of obtaining the nutrient (GA induces C4
photosynthesis - a higher yielding method of photosynthesis that has a
poisonous byproduct, Ethylene induces root hairs to absorb more Oxygen
in the roots - this increases root surface area but makes the roots
more susceptible to disease or drying out ).
Another alternate way of getting needed resources is by freeing up
stored resource of the needed variety from vacuoles,
A third way is to inhibiting growth in the plant organ (root or shoot)
that is not responsible for gathering the nutrient and making sure
that nutrients are shunted to that organ that does. For instance
Gibberellin stops root growth, because roots don't make sugar. Also
ABA probably inhibits shoot growth and maybe Ethylene stops root
growth too since most of the gases come in through the leaves.
Finally hormone X should inhibit shoot growth since this organ does
not take in minerals.
Senescent hormones probably induce senescent in older non-efficient
plant parts that are sinks for the needed nutrient thus lowering the
overall need of the plant for that nutrient. Thus Gibberellin should
induce root senscence, Ethylene also root senescence, ABA - shoot
senescence and hormone X - older shoot leaf senescence.
Finally nutrients are extracted for the senescent older efficient
plant part and sent to the part that needs it. In fact this happens
every night at a regular rate favoring the new plant part over the old
and recycling nutrients from old inefficient cells to new promising
youngsters.