The activity, characterization and distribution of the nitrogen assimilation enzyme, glutamine synthetase, in jack pine seedlings

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Abstract
The extraction of glutamine synthetase (GS) from jack pine (Pinus banksiana Lamb.) tissue was facilitated by solubilization of the tissue with 1% or more Nonidet P-40 detergent. In contrast with procedures commonly used to extract GS from other plant tissues, highest recovery of GS was obtained when jack pine tissues were subjected to ultrasonic homogenization in the absence of PVP. Chromatography on DEAE-Sephacel showed that jack pine needles possess two isoforms of GS. Isoform GS1, which is generally associated with the cytoplasm, eluted at 90 mM KCl and accounted for 80% of total GS activity. Isoform GS2, which eluted at 280 mM KCl, is generally associated with the chloroplast and is thought to be active in the primary assimilation of ammonium in leaves. Thus GS2 activity may be important if conifers are to avoid ammonium toxicity under circumstances, such as exposure to nitrous oxides, where nitrate reductase activity is induced in needles. In June, 72% of total GS activity was located in needles. Near the end of the growing season in August, however, only 1% of total GS activity was found in needles whereas 79% was found in roots.

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