Changes in the activities of chloroplast and cytosolic isoenzymes of glutamine synthetase during normal leaf growth and plastid development in wheat |
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Authors: | Alyson K. Tobin Stuart M. Ridley George R. Stewart |
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Affiliation: | (1) Department of Biology, University of York, Y01 5DD York, UK;(2) Jealott's Hill Research Station, ICI Plant Protection Division, RG12 6EY Bracknell, Berkshire, UK;(3) Department of Botany, Birkbeck College, University of London, Malet Street, WC1E 7HX London, UK;(4) Present address: Department of Biochemistry, University of Sussex, Falmer, BN1 9QG Brighton, Sussex, UK |
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Abstract: | Soluble protein extracts and chloroplasts from a serial sequence of transverse sections of a 7-d-old wheat leaf (Triticum aestivum cv. Maris Huntsman) were used to study changes in the activity of glutamine synthetase (GS; EC 6.3.1.2) during cell and chloroplast development. Glutamine synthetase activity increased more than 50-fold per cell from the base to the tip of the wheat leaf. Two isoenzymes of GS were separated using fast protein liquid chromatography (FPLC). Glutamine synthetase localized in the cytoplasm (GS1) eluted at about 0.21 M NaCl, and the isoenzyme localized in the chloroplast (GS2) eluted at about 0.33 M NaCl. The increase in GS activity during leaf development was found to be caused primarily by an increase in the activity of the chloroplast GS2. The activity of the cytoplasmic GS1 remained constant as the cells were displaced from the base to the tip of the leaf, whereas GS2 activity increased within the chloroplast throughout development. At the base of the leaf, 26% of total GS activity was cytoplasmic; the remaining 74% was in the chloroplast. At 10 cm from the base, only 4% of the activity was cytoplasmic, and 96% was in the chloroplast. The results indicate that the chloroplast GS2 is probably responsible for most of the ammonia assimilation in the mature wheat leaf, whereas cytoplasmic GS1 may serve a role in immature developing leaf cells.Abbreviations FPLC fast protein liquid chromatography - GS glutamine synthetase - GS1 cytoplasmic glutamine synthetase - GS2 chloroplast glutamine synthetase |
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Keywords: | Chloroplast development Glutamine synthetase Leaf development Triticum (isoenzymes) |
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