PNL Volume 14
Jacobsen, E. and I. van Dongen
University of Groningen, Dept. of Genetics, Haren, The Netherlands
Nitrate reductase (NaR) deficient mutants have recently been iso-
lated in Pisum sativum (1,3). In NaR deficient mutant E1 (1) nitrate
reduction is impaired but uptake is intact. In wildtype peas nodule
formation (5), nodule growth (5), and acetylene reduction (4) normally
are inhibited after supplying the plant with nitrate. Therefore, NaR
deficient mutants can be used to investigate whether the inhibition is
caused by the presence of nitrate itself in the plant or is brought
about by the reduction of this compound. In recent work (2) the effect
of nitrate on acetylene reduction in the mutant was investigated.
The results indicated that nitrate itself was not the inhibiting factor
but that reduction is involved.
In the present study the effect of nitrate on nodulation and total
nodule growth was examined. Preliminary results are shown in Tables 1
and 2. A concentration of 15 mM nitrate was chosen (5). Under these
conditions, the old leaves in some mutant plants became necrotic before
I nodulation characteristics were examined as a result of nitrate
accumulation. In the control, nitrogen-free mineral solution (SMS,1) +
15mM KC1 was used. Nodulation of E1 was 2 days later and nodule weight
per plant was higher in cv. 'Rondo' (cv. Rondo 0.34g; E. 0.28g). In
ether studies, with lower KC1 concentration in the control, nodulation
c laracteristics in cv. 'Rondo' and did not differ, indicating that
| t.e difference in nodulation with 15 mM presumably was due to the high
concentration used.
Table 1. Nodulation of cv. 'Rondo' and mutant E. after supply of 15 mM
KC1, 7.5 mM NH4NO3 or 15 mM KNO3.
In the studies on nodule formation, seeds and seedlings were
treated with SMS+15 mM KC1, SMS+7-5 mM NH4NO3, or SMS+15 mM KN03 from
the onset of the experiment and were analyzed^ 30 days after germination.
Treatment with NH4NO3 as well as with KN03 affected both the number of
root nodules and the nodule weight (Table 1). Nodulation on lateral
roots was almost completely absent (data not shown). In E1 the inhibi-
tion of nodulation on the main root was more severe. It is known that
nitrate is accumulated in E1 (1). Therefore these results indicate that
PNL Volume 14
for nodule formation, nitrate itself probably is the inhibiting factor
and under such circumstances nodule development is affected too.
Nodulation starts on the main root. Therefore, probably the best
impression about the effect of nitrate on nodule growth alone can be ob-
tained by studying weight increase of young nodules on the main root.
Application of nitrate to plants with young nodules simultaneously af-
fects other factors, especially on the lateral roots. The effect on
nodule growth has been investigated by treating nodulated plants 20 days
after germination with 15 mM KN03. Table 2 shows that 8 days after
treatment with nitrate nodule growth was impaired. There are indica-
tions that in E1 growth inhibition was less in nodules on the main root.
Further studies on nodule growth have been started in which the on-
set of nodulation has been synchronized by growing all plants on SMS
without addition of KC1 until the time of nitrate application. We tried
to avoid the development of necrotic symptoms completely by using lower
nitrate concentrations.
1. Feenstra, W. J. and E. Jacobsen. 1980. Theor. Appl. Genet. 5 8:39-
2. Feenstra, W. J., E. Jacobsen, A. C. P. M. van Swaay, and A. J. C.
de Visser. 1982. Plant Physiol, (in press).
3. Kleinhofs, A. , R. L. Warner, F. J. Muehlbauer, and R. A. Nilan.
1978. Mutation Res. 51:29-35.
4. Wilson, P. W. 1935. Wisconsin Research Bulletin 129:1-40.
5. Wong, P. P. 1980. Plant. Physiol. 66:78-81.