Comparison of in Vivo and in Vitro Assays of Nitrate Reductase in Wheat (Triticum aestivum L.) Seedlings

The effectiveness of the in vivo and in vitro assays for nitrate reductase (NR) in estimating the amounts of reduced N made available to plants was tested against the daily increases in reduced N (Nesslerization) actually accumulated by the plant. With growth-chamber-grown wheat seedlings, the average ratio values (input of reduced N as estimated by the in vitro assay to actual accumulation of N by the plant) were 3.9 for shoots, 3.7 for the roots, and 4.1 for the entire plant, over a 10-day period. With the in vivo assay, the average ratio values were 0.7 for the shoot, 1.8 for the root, and 0.9 for the entire plant. Although the linear regressions between the accumulated N in the plant and the estimated N input (by both in vitro and in vivo assays) were significant and positive, the in vivo assay provided the closest approximation of the actual amount of N accumulated.