Journal of Experimental Botany, Vol 49, 1827-1834, Copyright © 1998 by Oxford University Press
M Thorpe, K Walsh and P Minchin
The hypothesis that photoassimilate partitioning to the soybean nodule is
controlled by the rate of N export (via an effect on the turgor of the
unloading pathway) was tested. Cessation of N2 fixation due to exposure of
the nodulated root to Ar:O2 for over 3 h did not affect the partitioning of
photoassimilate to the nodule. In contrast, anaerobic conditions (100% N2)
resulted in a temporary cessation or marked slowing of carbon import into
the nodule and root organs, reflecting an O2 requirement of the unloading
process. Carbon accumulation by the nodulated root was less affected by a
rhizosphere treatment of 2% O2, although partitioning was decreased over a
period of hours. Treatment with 100% O2 also caused an immediate diversion
of photoassimilate from the root to the shoot system, although the extent
of this diversion was variable. Treatment with stepped increases in O2 did
not affect partitioning. It is concluded that the unloading kinetics of the
nodule were not disturbed by changes in nodule N metabolism, and therefore
that control of assimilate partitioning to the nodule is not influenced by
a turgor mechanism involving a balance between the primary export and
import solutes. However, photoassimilate import was matched to the
respiratory demand of the root system.Key words:
11C, nitrogen fixation, nodule, photoassimilate
partitioning, soybean.
ARTICLES
Photoassimilate partitioning in nodulated soybean III. The effect of changes in nodule activity shows that carbon supply to the nodule is not linked to nodule nitrogen metabolism
Horticulture and Food Research Institute, Ruakura Research Centre, Private Bag 3123, Hamilton, New Zealand; Department of Biology, Central Queensland University, Rockhampton 4702, Australia; Corresponding author e-mail: K.walsh@ccqu.edu.au
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