Re: can anthocyanins inhibit nitrate reductase activity?

I have found no evidence that anthocyanins are known inhibitors of nitrate reductase. It is widely known that nitrate reductase is an enzyme that has active site molybdenum atoms. And like other molybdo-enzymes it is inhibited by certain anions, like chlorate, vanadate, and tungstate. The expression of nitrate reductase is inhibited by various nitrogen-containing compounds like ammonium ions. There are also reports of certain plant proteins that naturally inhibit nitrate reductase activity. Control of gene expression is influenced by environmental factors as well, such as illumination regimes. In my opinion it seems unlikely that anthocyanins are directly inhibiting the nitrate reductase enzyme or its gene expression. I would ask you whether you have looked for protein expression using Western blots? Have you measured bioavailable nitrogen compounds? Your post seems to indicate that you are genetically modifying Arabidopsis by adding nitrate reductase genes. There are a host of reasons why you would not see increased expression and/or activity, including tissue specific responses. I include these references below, although I don't think that they are the key to your problems.

TI:  Growth of tobacco in short-day conditions leads to high starch, low 
sugars, altered diurnal changes in the Nia transcript and low nitrate 
reductase activity, and inhibition of amino acid synthesis.
AU:  Matt-P; Schurr-U; Klein-D; Krapp-A; Stitt-M
SO:  Planta. 1998 Dec; 207(1): 27-41

TI:  Inhibition of wheat leaves nitrate reductase activity by cibacron blue.
AU:  Albassam-BA
SO:  Biochem-Mol-Biol-Int. 1998 Dec; 46(5): 979-86

TI:  The effect of sugar mill effluent on enzyme activities of rice 
seedlings.
AU:  Behera-BK; Misra-BN
SO:  Environ-Res. 1985 Aug; 37(2): 390-8

TI:  Mode of action of natural inactivator proteins from corn and rice on a 
purified assimilatory nitrate reductase.
AU:  Solomonson-LP; Howard-WD; Yamaya-T; Oaks-A
SO:  Arch-Biochem-Biophys. 1984 Sep; 233(2): 469-74