Effects of Sucrose and Oxygen on Nitrate Reductase Activity and Growth of Kentucky Bluegrass

Abstract

Nitrate reductase activity (NRA) in turfgrass roots should play an important role in the N metabolism of the whole plant because a major part of the shoots is removed by mowing. However, preliminary experiments demonstrated a lack of in vivo NRA in roots of Kentucky bluegrass grown in Hoagland's nutrient solutions, which were constantly aerated. We hypothesized that O2 inhibited NRA by oxidizing carbohydrate available for NO3– reduction in roots. To test this hypothesis, Kentucky bluegrass (Poa pratensis L.), cultivar Merit, was grown in nutrient solutions containing 0.1 mM NO3–. Grass cultures were treated with +O2 (solution aerated), –O2 (not aerated), +Suc (sucrose added to solution, final concentration = 25 mM) or –Suc (not added) for 12 days. Plants were harvested at 5:00 pm, separated into shoots and roots, and analyzed for in vivo NRA. The results partly supported the above hypothesis because the –Suc–O2 roots showed significantly higher NRA than –Suc+O2 roots. However, +Suc roots did not exhibit greater NRA than –Suc roots, possibly because of a decreased pH in the solutions. Oxygen increased root growth and hence the growth of the whole plant, while sucrose decreased leaf N content and leaf NRA but did not improve growth.