Active nitrate pool size in wheat leaves cannot be accurately determined.
The researchers conducted experiments to understand how to measure nitrate levels in wheat leaves using a nitrate reductase assay. They found that the lack of nitrite accumulation, which indicates the active nitrate pool size, could be due to factors like oxygen levels, energy availability, or enzyme activity, not the availability of nitrate itself. They concluded that the assay used cannot accurately determine nitrate levels in wheat leaves.