Journal of Experimental Botany, Vol 49, 599-609, Copyright © 1998 by Oxford University Press
E James and R Crawford
The pasture legumes Lotus uliginosus (Schk.) and
Lotus corniculatus (L.), known to differ in their
tolerance to flooding, were inoculated with Rhizobium
loti and flooded for 60 d while subjected to two levels of
dissolved pO2: 0.241 and 0.094
ARTICLES
Effect of oxygen availability on nitrogen fixation by two Lotus species under flooded conditions
Plant Science Laboratories, Sir Harold Mitchell Building, University of St Andrews, St Andrews, Fife KY16 9AL, UK; Corresponding author
mol
ml-1. L. uliginosus showed
significantly greater growth (shoot and root) and N2 fixation under both
pO2s, compared to L. corniculatus, although growth and
N2 fixation by L. corniculatus was not affected by the
low pO2. Surprisingly, in L. uliginosus., growth,
nodulation and N2 fixation were all increased by low pO2 while nodulation
of L. corniculatus where low pO2 plants showed a
significant increase over that of the higher pO2 plants while L.
uliginosus plants showed a decline. Root porosity of
L. uliginosus doubled in the low pO2-treatment from a
mean of 14.5% in high pO2 roots to 28.5%, whereas that of L.
corniculatus was relatively unaffected by pO2, being 7% and 9%
for high and low pO2 plants, respectively. The structure of nodules
differed little between species and treatments, although nodules/nodulated
roots from the L. uliginosus plants had particularly
profuse lenticels and aerenchyma. However, L.
corniculatus nodules, especially those grown in the lower pO2
showed signs of early senescence with vacuolation of infected cells and
green coloration when cut open. Leghaemoglobin (Lb) concentrations in
nodules from both species were unaffected by low pO2, although that of
L. corniculatus nodules, regardless of pO2, was
significantly greater than L. uliginosus.
Concentrations of the intercellular glycoprotein recognized by the
monoclonal antibody MAC265 were significantly reduced in nodules from the
low pO2 treatment in both species. Immunogold labelling showed that the
MAC265 antigen was localized primarily within intercellular spaces within
nodule cortices from both Lotus species. A marked
decrease in deposition of the MAC265 antigen within the cortices of
L. uliginosus nodules grown in the lower pO2, is
discussed in terms of the relative abilities of the two
Lotus spp. to maintain an O2 supply to the N2-fixing
bacteroids within submerged nodules.Keywords:
Lotus uliginosus, Lotus corniculatus, N2
fixation, flooding, oxygen.
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