Reducing nitrate reductase activity in tabacco and methods for its use

A tobacco plant comprising a nitrate reductase in which the amino acid residue corresponding to position 525 in an amino acid sequence having 90% or more sequence identity with—the amino acid sequence of SEQ ID NO:

• 2 or 4 is mutated from proline to leucine or serine,
• wherein the tobacco plant has the properties (a) to (c):
• (a) activity of the nitrate reductase under a dark condition is 80% or more of activity of the nitrate reductase under a light condition;
• (b) growth characteristics of an individual plant for height of the plant, number of leaves on the plant, the size of leaves on the plant and the dry matter weight of leaves above the ground are the same as or the difference is 20% or less different from a control;
• and
• (c) nitric acid decreases as compared with the control, and
• wherein the control is a tobacco plant comprising a nitrate reductase consisting of the amino acid sequence of SEQ ID NO:
• 2 or 4.