A CHLORATE RESISTANT NITRATE REDUCTASE-DEFICIENT PEA MUTANT

PNL Volume 12 1980

RESEARCH REPORTS 11

Feenstra, W. J. and E. Jacobsen

University of Groningen, Haren, The Netherlands

Kleinhoffs et al. (3) isolated nitrate reductase (NaR)-deficient

mutants of Pisum by screening M2 families for a lower in vivo NaR-activity.

A less laborious way for the isolation of NaR-deficient mutants is

selection for chlorate resistance. This method has been applied success-

fully to bacteria (2) and to the higher plants Arabidopsis thaliana (5)

and Nicotiana tabacum (4). We have carried out this method on Pisum and

now want to report the isolation of a NaR-deficient mutant.

Seeds of cv 'Rondo' were treated with EMS. Among 7630 seedlings

belonging to 1090 M2 families one chlorate resistant mutant was found.

Experimental details will be published elsewhere. The mutant proved to

be monogenic and recessive. Biochemical characterization of leaf material

from 16-day-old plants yielded the following data (the comparable data of

the parent variety, Rondo, are given between brackets): in vitro NaR-

activity 0.08 (2.2) mkmol N0₂^-/g fresh weight/h; in vivo NaR-activity 0.19

(0.86) mkmol N0₂^-/g fresh weight/h; protein content 2.9 (3.6) mkg/g fresh

weight; nitrate content 75.2 (7.2) m aeq/g fresh weight. The original mutant

plant and its selfed progeny showed poor growth in soil and necrosis of leaf-

lets. The necrosis started with the oldest leaves when the plants were

still very young. Consequently the plants flowered poorly and yielded only

a few seeds.

Mutant plants cultured on a liquid nutrient medium with NH₄NO₃ as a

nitrogen source showed vigorous growth and no necrosis, and yielded about

as many seeds as cv Rondo cultured in the same way.

Preliminary studies showed that necrosis does not appear in plants

grown on a liquid culture medium without nitrogen, but it is readily evoked

by growing the mutant on a nutrient solution containing NO₃^- as the sole

nitrogen source. The results suggest a toxic effect of accumulated nitrate,

whereas the protecting influence of NH₄⁺ may either be brought about via

an improved protein synthesis or by an inhibition of nitrate uptake (1).

1. Doddema, II. and G. P. Telkamp. 1979. Physiol. Plant. 45:332-338.

2. Groot, G. N. de and A. H. Stouthamer. 1969. Arch. Mikrobiol.

66:220-233.

3. Kleinhoffs, A., R. L. Warner, F. J. Muehlbauer, and R. A. Nilan. 1978.

Mutation Res. 51:29-35.

4. MUller, A. J. and R. Grafe. 1978. Molec. Gen. Genet. 161:67-76.

5. Oostindier-Braaksma, F. J. and W. J. Feenstra. 1973. Mutation Res.

19:175-185.