Water relations parameters of the phloem. Determinations of volumetric elastic modulus and membrane conductivity using an applied force method and shrinkage and swelling of tissues in solutions at differing osmotic pressure

• Published in: Annals of botany Vol. 51; no. 1; pp. 27 - 37
• Main Authors: Sovonick-Dunford, S, Ferrier, J.M, Dainty, J
• Format: Journal Article
• Language: English
• Published: Oxford University Press 1983; Academic Press Inc
• Subjects: biltmoreana (Beadle) J. Wright; Elastic tissue; Fraxinus americana var; Hydraulic conductivity; membrane hydraulic conductivity; Moduli of elasticity; Osmosis; Phloem; Plant cells; Plant tissues; Quercus borealis michx. f; Quercus rubra; red oak; Sieve elements; Swelling; Turgor pressure; volumetric elastic modulus; water relations; white ash
• ISSN: 0305-7364; 1095-8290
• DOI: 10.1093/oxfordjournals.aob.a086447

Water-relations parameters were measured on sections of secondary phloem from red oak (Quercus borealis michx. f.) and white ash (Fraxinus americana var. biltmoreana [Beadle] J. Wright) using a linear displacement transducer. Changes in tissue thickness in response to changes in the osmotic pressure of the bathing solution were used to calculate the volumetric elastic modulus plus osmotic pressure (εv + Π) of the tissue, and an applied force method was used to estimate the time constant for water equilibration (T). The hydraulic conductivity of the cell membranes (Lp) was calculated utilizing εv + Π and r values. The time-dependent behaviour of the tissue was much more complex than originally expected. A correction for a time-dependent process that we call ‘drift’ was required to obtain numbers for εv + Π. Furthermore, εv + Π was calculated on two assumptions in order to relate changes in tissue dimensions to sieve element parameters. In the first case, a lower limit for εv + Π of the sieve elements was determined by attributing all changes in tissue dimensions to these cells. For red oak the average εv + Π on this assumption is 72 bars. Assuming that all cell types were equally responsible for the changes in tissue dimensions resulted in an εv + Π value of 192 bars for oak. If εv + Π and r are the same for all cells in the tissue, Lp for the sieve elements of oak is 9.6 × 10−8 cm s−1 bar−1. Exudation from the sieve elements of white ash during excision of the phloem led to artificially high values of εv + Π for that species.