Nitrate Reductase Deficient Mutants of Chlamydomonas reinhardii. Biochemical Characteristics

Abstract

Two mutants of Chlamydomonas reinhdrdii that cannot grow with nitrate as nitrogen source have been examined biochemically. Each mutant differs from the wild-type strain by a single mutation in a Mendelian gene. One mutant (141 15) carries a mutation in a gene designated nitB. This organism took up nitrate and converted nitrate-nitrogen to insoluble-nitrogen; nevertheless no enzymic activities associated with nitrate reductase (NADH-nitrate reductase, reduced benzyl viologen nitrate reductase or inducible NADH-cytochrome c reductase) could be demonstrated in frozen/thawed cells or cell-free extracts. At high nitrate concentrations (5 mM) the rate of nitrate uptake by this mutant [Vma, 59 nmol (mg dry wt)-l h-l] was considerably lower than that of wild-type [Vmax 920 nmol (mg dry wt)-l h-I]. It is concluded that nitB is probably a regulatory gene for nitrate reductase. The other mutant (17/4) has a mutation in a gene designated nitA. This organism did not take up nitrate and had no NADH-nitrate reductase or inducible NADH-cytochrome c reductase activities. Frozen/thawed cells and cell-free extracts had reduced benzyl viologen nitrate reductase activity. The enzyme from the nitA mutant eluted from a Sepharose 4B column later than wild-type enzyme; it was therefore probably of lower molecular weight. The nitA mutation of C. reinhardii closely resembles the nit-3 mutation of Neurospora crassa and, like this mutation, it probably results in loss of the NADH combining sub-unit of nitrate reductase. Strain 137c of C. reinhardii had no enzymic activities associated with nitrate reductase and did not take up nitrate. This organism may have mutations in both the nitA and nitB loci.

Glutamine Synthetase Isoforms in Algae

“…Similarly C. reinhardii 17/4A (mutant of the wild type 6145C), although a chlorophyllous alga, is a nitrate reductase mutant. The mutation is in a single gene producing an incomplete nitrate reductase protein hence the alga is unable to grow on nitrate (Nichols, Shehata & Syrett, 1978). Thus the absence of GSg may be induced because of absence of nitrite reduction leading to production of ammonium for assimilation.…”

Central Carbon Metabolism and Electron Transport in Chlamydomonas reinhardtii: Metabolic Constraints for Carbon Partitioning between Oil and Starch

“…The starchless mutant from Steven G. Ball (96) (BAFJ5 strain), which is the flagship algal strain for lipid production (82), has major genetic lesions. In addition to the nit1 nit2 mutations that prevent algal cells from growing when nitrate is the sole nitrogen source (97), this mutant is cw15 sta6, which denotes that it lacks both a cell wall and the ADP-glucose pyrophosphorylase; the latter enzyme catalyzes the first committed step in starch biosynthesis (96). The BAFJ5 strain therefore lacks two major carbon sinks, cell wall glycoproteins (with arabinose, mannose, galactose, and glucose being the predominant sugars), and starch granules.…”

Effect of Pesticide on Nitrate Reductase Activity in Trigonella Foenum i.e., Fenugreek

“…The nitrate reductase activity is inhibited by heavy metals like Cr 3+ and Cu 2+ irreversibly [10]. It has also been reported that insecticides (kelthane and fenvalerate) caused some inhibition to enzyme activities [6]. In some experiments 15 different pesticides were evaluated to study their effect on growth and nitrogen assimilation of the Azolla Mexicana [11].…”

“…Nitrate reduction processes are perhaps most significant in maintaining water quality. NR enzyme is responsible not only for nitrate reduction, but also for nitrate uptake in Chlamydomonas, Chlorella sorokiniana [5,6]. Assimilatory Nitrate reduction, performed by a variety of bacterial and eukaryotic organisms [7,8] includes the reduction of nitrate and nitrite compounds, often mediated by nitrate or nitrite reductase enzymes, for synthesis of amino acids.…”