In article <94089.122853FSL at psuvm.psu.edu>, Dan Cosgrove
<FSL at psuvm.psu.edu> wrote:
> On 29 Mar 1994 Kate at tamsun.tamu.edu quoted some un-named who wrote:
> > From my reading it generally appears that most plant physiologists
> > believe the cell walls "loosen" prior to elongating. I have trouble
> > with "loosening" as a word to discribe what happens....
> The concept of wall "loosening" arises largely from biophysical argument.
> It goes as follows: Because growing cells are thin-walled vessels with
> turgor pressures of 3-8 atm or so, the walls carry a large tensile
> stress, something of the order of 1000 atm static stress. This is only
> possible if the wall has great mechanical strength. To make such a
> tough, load-bearing network expand in surface area, without rupture, is
> not trivial. It is not just a matter of "actively growing", say, by
> depositing more material to the wall. Rather, wall stress must first
> be reduced by some sort of re-arrangement of the load-bearing wall polymers.
> This reduces the cells water potential and allows the cell to take up
> water, which physically expands the wall. This re-arrangement, leading to
> stress relaxation, is what is meant by "loosening". The biochemical
> nature of "loosening" (or more correctly, stress relaxation) is another
> story - more complicated and still full of debate.
> Dan Cosgrove
>FSL at PSUVM.PSU.EDU
It was I who was quoted - and thanks for your response.. I remain
unconvinced that a "loosening agent" is necessary. Though my thoughts are
on the intuative side your hypotheses stimulate my thinking.
Kate at tamsun.tamu.edu commented that hydrogen bonds between gluccans need to
be "broken" for cell wall extension to occur. It would be my theory that
in young - small cells there are only so many H-bonds which can occur and
there number and strength are insufficient to restrain cell wall expansion.
As the cell grows - lengthens - the number of "sites" for H-bonding would
increase and the aggregate strength of these bonds would be what eventually
Also the force supplied by turgor pressure would decline as the cell
expands - though more water may be imported into the cell to maintain the
turgor. This movement of water into a cell to maintain turgor maybe under
the control of the plasmalemma and tonoplast - controlling the movement of
solutes (K) into the cell. Also the formation of osmotica be cells maybe
controled through the cell aging process.
This - I agree - is a very interesting topic.
Thanks again for your responses
What a long strange trip its been