MadSci Network: Botany

Re: Plant transpiration with .01M of sugar water

Date: Mon May 22 21:23:19 2006
Posted By: David Hershey, Faculty, Botany, NA
Area of science: Botany
ID: 1148270564.Bt

I'm not sure I have the right answer but can provide some possibilities.

Both potassium ion and sucrose concentrations in guard cells correlate with
stomatal opening. (Talbott and Zeiger, 1996). Lua et al. (1995) found that the
sucrose concentration in guard cells was highest when stomata were open. Outlaw
and Vlieghere-He (2001) found that with a high transpiration rate, sucrose
concentration in the guard cell walls of bean plants increased and caused the
stomatal aperature to decrease. 

I'm not sure exactly how you were measuring transpiration but assume it was some
kind of potometer. With potometers that use volume or flow measurements, you
cannot differentiate between water that is absorbed and retained by the twig and
water that is absorbed and transpired. (Potometers that measure weight loss do
not have this problem). Twigs soaked in a sucrose solution would absorb a
sucrose solution that had a lower water potential than the tap water. When the
twigs were later placed in tap water, they could have absorbed more tap water
because of their lower water potential due to the sucrose solution they
absorbed. Thus, the twigs soaked in the sucrose solution might appear to be
transpiring more but in reality they could have simply been absorbing additional
water because of their lower water potential. 

Lua, P., Zhangb, S.Q., Outlaw, W.H. Jr. and Riddlea, K.A. 1995.Sucrose: a solute
that accumulates in the guard-cell apoplast and guard-cell symplast of open
stomata. FEBS Lett. 362(2): 180-184.   

Outlaw, W.H. Jr. and Vlieghere-He, X.D. 2001. Transpiration Rate. An Important
Factor Controlling the Sucrose Content of the Guard Cell Apoplast of Broad Bean.
Plant Physiology 126: 1716-1724.

Talbott, L.D.and Zeiger, E. 1996. Central Roles for Potassium and Sucrose in
Guard-Cell Osmoregulation. Plant Physiology 111(4): 10511057.

The Clickable Guard Cell: Electronically linked Model of Guard Cell Signal
Transduction Pathway

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