NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/bionet/plants/783

Internet Message Format | 1992-12-23 | 3.0 KB

Path: sparky!uunet!mcsun!uknet!daresbury!news
From: [e-mail] (Tony Travis)
Newsgroups: bionet.plants
Subject: Re: Plant communication/sensing references
Message-ID: <[e-mail]>
Date: 23 Dec 92 10:27:36 GMT
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Distribution: bionet
Organization: Rowett Research Institute
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In article <[e-mail]> you wrote:
:
: [... discussion about action potentials ...]
:
: >So far there are several classes of channels that have been
: >characterised.  The main one is the inward rectifying potassium channel.
: >If I remeber right, it has a small sodium conductance, but that is
: >irrelevant given the very low sodium concentrations.

I agree about low Na+ concentrations.  Active K+/Na+ 'antiport' in
animal cells involves the exchange of K+ and Na+ ions across the
membrane at the same site.  In plants, the active process is H+
extrusion by membrane bound ATPases and the K+ (or other) influx is
moderated by ion-conducting channels elsewhere in the membrane.

As others have pointed out on this thread, the amount of Na+ normally
present in plants is low compared to the levels in animal cells and K+
is the major cation present in the majority of plant cells.  Active K+
transport into plant cells is one of the mechanisms controlling cell
turgor and the availability of K+ in the apoplast is therefore an
important factor in determining the K+ influx into the cell.

It seems a reasonable proposition to me that the signal propagated from
cell to cell in the responses of mimosa may be associated with a 'wave'
of fluctuations in the concentrations of K+ ions in the apoplast.
This, I accept, may be conceptually similar to the action potential
observed in transmission of nerve impulses, but does not require K+/Na+
antiport to occur.

There has also been considerable debate in the literature about the
role of Cl- in plants and, in stomatal guard cells, Schnabl
demonstrated that Cl- reduced the amount of malate accumulation
associated with K+ influx into guard cells during stomatal opening. It
seems that plants will use Cl- if it is available, but will synthesise
organic anions such as malate when no other anion is avaialble.

This topic has been discussed in the plant biology literature for many
years, and I think the 'age' of the literature references cited is
relevant if subsequent work contradicts it, but simply to dismiss work
on the grounds that "it was published in 1976" is absurd.  Equally, it
is absurd to dismiss the important work done on active ion transport in
animal cells when discussing ion transport in plants but the mechanisms
are NOT the same and that needs to be taken into account.

    Tony.

ps. I did some of my work on this topic in 1976 ;-)
--
Dr. A.J.Travis,                       |  Tony Travis
Rowett Research Institute,            |  JANET: <[e-mail]>
Greenburn Road, Bucksburn,            |  other: <[e-mail]>
Aberdeen, AB2 9SB. UK.                |  phone: [phone]