Journal of Experimental Botany, Vol 49, 1789-1796, Copyright © 1998 by Oxford University Press
V Romanov, A Gordon, F Minchin, J Witty, L Skot, C James and I Tikhonovich
In contrast to the classification of FN1 as a fix minus mutant (Postma
et al., 1990), in these experiments, nodules of the
FN1 mutant (formed by Rhizobium leguminosarum RCR 1045) showed acetylene
reduction activity, but at a much lower level than in the Rondo parent
line. The presence of nitrogenase was confirmed by immunodetection.
Microelectrode measurements of O2 gradients across the nodule cortex
indicated that the oxygen diffusion barrier in mutant nodules appeared to
be functioning normally. Leguhaemoglobin (Lb) haem concentration in FN1
nodules was only 40% and 25% of that in the Rondo parent line at 3 and 4
weeks, respectively, whereas immunodetection of the apoprotein suggested
reductions to 57% and 46%, respectively. FN1 nodules also contained
substantially lower amounts of ononitol, aspartate and asparagine in
comparison with Rondo nodules. Sucrose concentration was similar, but
starch content was 2-fold higher in the mutant nodules. Of the 15 enzymes
of C and N metabolism investigated, only sucrose synthase,
phosphoenolpyruvate carboxylase, alanine pyruvate aminotransferase,
glutamine synthetase, and glutamate synthase were significantly lower in
the nodules of the FN1 mutant. In contrast to other fix minus or fix
impaired mutants, alcoholic fermentation was not induced in FN1
nodules.Key words: Peas, nodules, mutant, enzymes,
nitrogen fixation.
ARTICLES
Physiological and biochemical characteristics of FN1, a 'fixation impaired' mutant of pea (Pisum sativum L.)
AN Bach Institute of Biochemistry, Leninsky Prospect 33, Moscow 117071, Russia; Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth, Ceredigion, Wales SY23 3EB, UK; All-Russia Institute for Agricultural Microbiology, Shosse Podbelsky 3, St Petersburg-Pushkin 188620, Russia; Corresponding author e-mail: frank.minchin@bbsrc.ac.uk
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