PNL Volume 12 1980
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.
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.