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- Title
Diurnal variation in the radial reflection coefficient of intact maize roots determined with xylem pressure probe.
- Authors
Schneider, H.; Wistuba, N.; Miller, B.; Geßner, P.; Thürmer, F.; Melcher, P.; Meinzer, F.; Zimmermann, U.
- Abstract
Xylem pressure and its relative response to the imposition of an external osmotic stress (the so-called radial reflection coefficient) were recorded in roots of intact maize plants using the xylem pressure probe technique. Consecutive insertion of two probes into the same xylem vessel or into adjacent vessels of intact roots of plants exposed to high light intensity and salt stress under laboratory conditions showed that the xylem tension was not changed by vessel probing. It was also shown by using the double probe approach that the plants were capable of overcoming artificially induced leakages. This and other evidence reported in the literature convincingly demonstrated that the probe accurately reads xylem pressure and xylem pressure responses to osmotic stress. Additional experiments were performed on plants grown in a greenhouse at a subtropical latitude. Under these conditions the plants were exposed to strong diurnal fluctuations in light intensity, relative humidity and temperature. The results showed that the absolute xylem pressure in the roots of untreated plants decreased with increasing transpiration rate from positive values in the early morning to negative values around noon (average value -0.15 MPa; maximum negative value -0.57 MPa). As the day progressed and the transpiration rate decreased, xylem pressure increased again to positive values. Correspondingly, the radial reflection coefficient for NaCl increased from about zero in the early morning to about unity at noon when transpiration reached its highest value and decreased again to very low values towards the evening. The data raise questions concerning conclusions about the mechanism of water transport in intact roots drawn from the low radial refection coefficients measured on excised roots using the root pressure probe.
- Subjects
CORN; PLANT roots; XYLEM; OSMOSIS; PLANT transpiration
- Publication
Journal of Experimental Botany, 1997, Vol 48, Issue 317, p2045
- ISSN
0022-0957
- Publication type
Article
- DOI
10.1093/jexbot/48.317.2045