PNL Volume 14

1982

RESEARCH REPORTS 23

EFFECT OF NITRATE ON NODULATION IN A NITRATE REDUCTASE DEFICIENT PEA

MUTANT

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

1982

RESEARCH REPORTS

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-

42.

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.