Plant Physiol, May 2000, Vol. 123, pp. 139-148
Gradients in Water Potential and Turgor Pressure along the
Translocation Pathway during Grain Filling in Normally Watered and
Water-Stressed Wheat Plants1
Donald B.
Fisher* and
Cora E.
Cash-Clark2
Department of Botany, Washington State University, Pullman,
Washington 99164-4238
The water relations parameters involved in assimilate flow into
developing wheat (Triticum aestivum L.) grains were
measured at several points from the flag leaf to the endosperm cavity
in normally watered (
0.3 MPa) and water-stressed plants
( 2 MPa). These included direct measurement of sieve tube
turgor and several independent approaches to the measurement or
calculation of water potentials in the peduncle, grain pericarp, and
endosperm cavity. Sieve tube turgor measurements, osmotic
concentrations, and measurements using dextran microdrops showed
good internal consistency (i.e. = s + p) from 0 to 4 MPa. In normally watered plants, crease
pericarp and sieve tube turgor were almost 1 MPa lower than in the
peduncle. This suggests a high hydraulic resistance in the sieve tubes
connecting the two. However, observations concerning exudation rates
indicated a low resistance. In water-stressed plants, peduncle and
crease pericarp were similar. In both treatments, there was a
variable, approximately 1-MPa drop in turgor pressure between the grain
sieve tubes and vascular parenchyma cells. There was little
between-treatment difference in endosperm cavity sucrose or osmotic
concentrations or in the crease pericarp sucrose pool size. Our results
re-emphasize the importance of the sieve tube unloading step in the
control of assimilate import.
1
This work was supported by the National Science
Foundation (grant no. IBN-9514188).
2
Present address: e-mail
tclark2{at}iusb.edu.
*
Corresponding author; e-mail dbfisher{at}wsu.edu.
© 2000 American Society of Plant Physiologists
