Molybdenum as a Plant Nutrient. X. Some Factors Affecting the Activity of Nitrate Reductase in Cauliflower Plants Grown with Different Nitrogen Sources and Molybdenum Levels in Sand Culture

Abstract

Nitrate reductase activity in crude extracts of cauliflower tissue has a pH opt. 7.2. The activity is high in plants grown with nitrate or nitrite and low with ammonium sulphate. Activity is greatly decreased by Mo deficiency and is not restored by giving Mo to extracts, but increases slowly on giving Mo to intact tissues. The activity is greatest in mature but not senescent leaves. Net activity per unit fresh wt. is greater in leaves than petioles stems or roots. 4-6 Days darkness or 2 days without air sharply decreases activity in extracts and this recovers in 3-12 hours in normal environment. Nitrate reductase in higher plants may be adaptive with respect to both N and Mo supplies and requires normal daylight and air to remain active in living plants.