Effects of age and variety on nitrate reductase and nitrogen fractions in potato plants

The effects of plant age and variety on the level of nitrate reductase activity in three varieties of Solanum tuberosum (Kennebec, Norchip and Early Ohio) have been studied by assaying nitrate reductase at different intervals during growth and development. Nitrate reductase appears to be localised in leaves and young stems. Negligible nitrate reductase activity was recorded in roots and tubers. The varieties differed significantly in nitrate reductase activity and the tuber protein nitrogen content paralleled the level of activity in leaves. The levels of nitrate reductase activities in leaves were also highly positively correlated with quantities of leaf inorganic nitrogen, protein and free amino acids. The activity began to decline at about 50 days after emergence, and this may be a useful indicator of when to apply nitrogen fertiliser so as to increase tuber protein content.