Changes in Reduction and Assimilation of Nitrogen During the Growth Cycle of Winter Wheat1

Abstract

Changes in nitrate reductase activity and nitrate and water‐soluble protein contents of field‐grown ‘Pawnee’ wheat were studied throughout the growth cycle.Crown tissue was analyzed during cold hardening and dehardening periods. Nitrate reductase activity was initially low, increased slightly during maximum hardening, and increased rapidly with dehardening. Water‐soluble protein and nitrate contents decreased with hardening and increased with dehardening.During spring, aerial plant parts were analyzed separately. Nitrate reductase activity and water‐soluble protein contents were highest in the blades, with decreasing levels in sheaths, heads, and culms, respectively. Nitrate concentrations were highest in the culms, with less in sheaths, blades, and heads, respectively. Upper blades and sheaths contained greater nitrate reductase activity and water‐soluble protein, while nitrate concentrations were highest in lower blades and sheaths. All components measured decreased with maturity in all plant parts. Significant positive correlations were found between nitrate reductase activity and water‐soluble protein and between nitrate reductase activity and nitrate in crown, blade, and sheath tissues when these factors were compared within plant parts over sampling dates.