Journal of Experimental Botany, Vol 49, 1845-1854, Copyright © 1998 by Oxford University Press
M Proctor, Z Nagy, Z Csintalan and Z Takacs
The water associated with a bryophyte can be divided into (a) apoplast
water held in cell-wall capillary spaces and by matric forces, (b) osmotic
(symplast) water, and (c) external capillary water. In many bryophytes (c)
is a large and variable component, preventing easy determination of
full-turgor water content and of relative water content (RWC) values
physiologically comparable with those for vascular-plant leaves.
Pressure-volume (P-V) curves are presented and
water-relations parameters estimated for bryophytes, including species with
large thin-walled cells (Hookeria lucens and three
marchantialian thalloid liverworts), species with notably thick cell walls
(Neckera crispa), and species with wettable surfaces
and well-developed external capillary water conduction (Tortula
ruralis, Anomodon viticulosus), and for the lichen
Cladonia convoluta. Full-turgor water content ranged
from c. 110% DW. in T. ruralis and Andreaea
alpina to 1400% DW or more in Dumortiera
hirsuta and Conocephalum conicum. Osmotic
potential (
ARTICLES
Water-content components in bryophytes: analysis of pressure-volume relationships
Department of Biological Sciences, University of Exeter, Hatherly Laboratories, Prince of Wales Road, Exeter EX4 4PS, UK; Department of Botany and Plant Physiology, Agricultural University of Godollo, Páter K. u. 1, H-2103 Godollo, Hungary; Corresponding author e-mail: M.C.F.Proctor@exeter.ac.uk
) at full turgor was between -1.0 and -2.0
MPa in most species, but substantially less negative values were found in
the thalloid liverworts (-0.35 to -0.64 MPa). The
x-intercept of the P-V curve is
not a reliable estimate of apoplast volume and may give negative values;
better estimates of apoplast volume may be obtained by vapour equilibration
at known low water potentials. Blotting external water from shoots usually
gave full-turgor water content estimates in reasonable agreement with those
obtained by analysis of P-V curves, but for different
reasons they could be either higher or lower than the true value. The
importance of knowing full-turgor water content for physiological work on
water-stress responses in bryophytes is emphasized.Key
words: Thermocouple psychrometry, apoplast fraction, relative
water content, osmotic potential, poikilohydry.
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