Enzymatic Metabolism of Nitrogen in Leaves and Roots of Creeping Bentgrass under Nitrogen Deficiency Conditions

Abstract

Low nitrogen (N) rates are recommended for creeping bentgrass (Agrostis stolonifera) putting greens to prevent excessive shoot growth and potential nitrate leaching, but low N rates could lead to N deficiency, which induces leaf senescence. This study was conducted to examine the effects of N deficiency on two enzymes involved in organic N metabolism as well as amino acid (AA) and soluble protein (SP) contents in both young and old leaves and roots of creeping bentgrass. Creeping bentgrass plants (cv. Penncross) were grown in a nutrient solution containing either 6 mm nitrate (+N plants) or zero N (−N plants), and each of the two treatments had four replicate pots. Young leaves on upper portions of the stolons and old leaves on lower portions of the stolons were separated and sampled at 14, 21, and 28 days of treatment, and roots were sampled at 28 days. Nitrogen deficiency increased glutamine synthetase (GS) transferase activity in all three tissues and at all three dates and GS biosynthetic activity in young leaves at all three dates. Prolonged N deficiency at 21 and 28 days increased glutamate dehydrogenase (GDH) deamination and amination activities in old leaves. In the roots, N deficiency at 28 days increased GS transferase activity but decreased GDH deamination activity. The N deficiency decreased AA content in all three tissues and at all three dates and SP content in young leaves at all three dates and in old leaves at 21 and 28 days. Decreasing organic N reserves in AA and SP and increasing GS and GDH activities in senescing leaves may be adaptive responses to N deficiency.