Nitrate reduction in the wildtype and a nitrate reductase deficient mutant of Arabidopsis thaliana

Abstract

1982. Nitrate reduction in the wildtype and a nitrate reductase deficient mutanl of Arabidopsis thaliana. -Physiol. Plant. 54: 351-360.A chlorate-resistant mutant B25 of Arabidopsis thaliana (L.) Heinh. was isolated, which has very little or no in vitro nitrate reductase activity and grows poorly on a substrate with nitrate as the sole nitrogen source. The mutation of B25 (fgn) is monogenic and recessive, tightly linked to the marker gene an on chromosome 1. Nitrate induces cytochrome-c reductase activity in the mutant but to a lower level than in the wildtype. After sucrose gradient centrifugation the greatest part of the cytochrome-c reductase from induced wildtype is found as 8s type whereas cytochrome-c reductase from B25 under the same conditions is found as 4s type. Nitrate reductase is found at the 8s position. It is suggested that B25 has lost the ability to assemble two 4s siibunits showing cytochrome-t reductase activity and a Mo-bearing co-factor into the functional nitrate reductase. Nitrate rather than nitrite is the inducing agent for nitrite reductase, since in B25 nitrite reductase is even more rapidly induced than in the wildtype after addition of nitrate. Both the wildtype and B25 contain a nitrate reductase inhibiting factor when grown on ammonium. This inhibiting factor is a small protein, possibly similar to the nitrate reductase inactivating enzyme reported for other plants.

In vivo Nitrate Reductase Activity in the Seagrass Halophila stipulacea from the Gulf of Aqaba (Jordan)

“…Apparently these plants are adapted to extremely Iow levels of nitrate and have lost the ability to induce nitrate reductase when supplied with high nitrate concentrations. It cannot even be excluded that the Iow activity observed is, in fact, the activity of epiphytes, since Braaksma and Feenstra (1982) Manisch Ten Cate and Breteler (1981) Baer and Collet( 1981) Vance and Heichel( 1981) StuleneM/. (1981) SaadEddin and Doddema (1982) Doddema and Howari (present paper)…”

Comparison of the sequences of the Aspergillus nidulans hxB and Drosophila melanogaster ma‐l genes with nifS from Azotobacter vinelandii suggests a mechanism for the insertion of the terminal sulphur atom in the molybdopterin cofactor

“…As these molybdoenzymes carry out completely different functions, the authors proposed that single mutations resulting in a loss of both these activities could identify genes somehow involved in the biosynthesis of a common cofactor. Mutations with a similar biochemical phenotype were also identified in Drosophila , bacteria, plants and humans (Finnerty, 1976; Amy, 1981; Braaksma and Feenstra, 1982; Simmonds et al ., 1995).…”

Uptake of chlorate and other ions in seedlings of the nitrate‐uptake mutant B1 of Arabidopsis thaliana

“…Seedlings were grown aseptically in submerged ctiltures essentially as described by Braaksma and Feenstra (1982), About 200 seeds were germinated under continuous illumination (fluorescent light tubes, TL-33 Philips; 15 W m"') in Erienmeyer flasks (100 ml) with 20' ml nutrient solution at 25°C on a platform with a tilting movement at, low speed. The nutrient solution contained 6,5 mM nitrate and the concentration of sucrose was 0,25% (w/v) instead of 2% to avoid starch accumulating in the leaves.…”