PARENT SESSION
Poster Session 12: Physiology
Tuesday, August 9, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Changes in the activity of nitrate reductase in response to growth at elevated CO₂.

Constable, John^*,1, ¹ California State University, Fresno, CA

ABSTRACT- This study examined the effect of elevated growth CO₂ on the activity of nitrate reductase (NR), the first step in the assimilation of nitrate (NO₃^-), and foliar carbohydrate concentration. Measurements were performed at three Free Atmosphere CO₂ Enrichment (FACE) sites with different target species: Pinus taeda at Duke University, Liquidambar styraciflua at Oak Ridge National Laboratory, and C3 (Agropyron repens) and C4 (Bouteloua gracilis) grasses at the University of Minnesota. It was hypothesized that elevated CO₂ would (a) increase NR activity; (b) stimulate activity of root NR preferentially over foliar NR; and (c) enhance tissue carbohydrate storage. The activity of NR in root and foliage tissue was determined using an in vivo assay and the concentration of foliar carbohydrate (soluble sugars and starch) was assayed enzymatically. An ANOVA indicated that neither growth CO₂ (ambient vs. elevated), or tissue type (foliage vs. root) influenced NR activity in P. taeda. In L. styraciflua growth CO₂ did not effect NR activity in either tissue, but activity in foliar tissue exceeded that in root tissue (p=0.031). Similarly, in A. repens and B. gracilis, CO₂ did not change the activity of NR in either foliar or root tissue, but foliar NR activity was greater than root activity (p=0.005; p=0.008, respectively). Elevated growth CO₂ had no effect on the foliar concentration of soluble sugars or starch in P. taeda, whereas in L. styraciflua, soluble sugar and starch concentrations tended to increase (+14.7% and +13.0%, respectively). Foliar carbohydrates appeared to increase at elevated CO₂ in A. repens (soluble sugars +12.3% and starch +35.8%) and in B. gracilis (soluble sugars +30.7% and starch +6.6%). Although growth at elevated CO₂ appeared to increase foliar carbohydrate levels in several species, there was no significant change in either foliar or root activity of NR or the balance of NR activity between tissues.

Key words: Nitrate reductase, Elevated CO₂, Carbohydrate