Journal of Experimental Botany, Vol 49, 1387-1395, Copyright © 1998 by Oxford University Press
T Lawson, J Weyers and R A'Brook
The aim of this research was to investigate the nature of heterogeneity in
stomatal conductance and, in particular, to determine whether the
characteristic 'patchy' pattern of water infiltration is reflected in
measurements on individual stomata. Silicone rubber replicas were made of
primary leaves of glasshouse-grown Phaseolus vulgaris
L. plants, and the leaves were then infiltrated with water at controlled
sub-atmospheric gas pressures according to their estimated or measured
stomatal conductance. Seven leaves examined in detail all showed patchy
infiltration, and the mean sire of infiltrated areas was negatively
correlated with the prevailing stomatal conductance. In four of the leaves,
a one millimetre wide transect across the leaf was selected for further
detailed study. Measurements of mean peristomatal groove distance
(PGD) and stomatal frequency were made along the
transect and related to the state of infiltration. Analysis of variance
indicated that, in all four cases, variation in PGD
among patches was highly significant, but there was no significant
difference between patches of different infiltration categories. Thus,
local (patch-level) variation in stomatal aperture appeared to bear no
relation to the infiltration status of the patches. The dominant source of
stomatal variability was between individual pores in the same locality,
which accounted for 82% or more of the total variability. Taking into
account variation in stomatal frequency, correlations between predicted
stomatal conductance and the extent of infiltration were significant in
only one out of the seven leaves studied. Possible reasons for these
results are discussed. It is suggested that the infiltration method
misrepresents the underlying state of the stomata as being either open or
closed, when there is little evidence for this from measurements of
stomatal dimensions. For these unstressed plants under relatively stable
conditions, it is concluded that the 'unit of variability' in stomatal
heterogeneity may rest at the individual pore ('micro') scale, rather than
at the areolar patch ('macro') scale, or
above.Keywords: Conductance, heterogeneity,
infiltration, patches, stomata
ARTICLES
The nature of heterogeneity in the stomatal behaviour of Phaseolus vulgaris L. primary leaves
Department of Biological Sciences, University of Dundee, Dundee DD1 4HN, UK; Corresponding author; Present address: Cardiovascular Epidemiology Unit, University of Dundee, Dundee DD1 4HN, UK
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