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Glutamine synthetase isozymes in germinating barley seeds
Author(s) -
Marttila Salla,
Saarelainen Ritva,
Porali Ilkka,
Mikkonen Anita
Publication year - 1993
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1993.tb01379.x
Subject(s) - scutellum , aleurone , hordeum vulgare , germination , caryopsis , glutamine synthetase , protein subunit , biology , biochemistry , immunogold labelling , isozyme , cytosol , endosperm , enzyme , botany , poaceae , glutamine , ultrastructure , gene , amino acid
Glutamine synthetase (GS; EC 6.3.1.2) is a key enzyme of ammonia assimilation in higher plants. In the present study the subunit composition and localization of GS in germinating barley ( Hordeum vulgare ) seed have been clarified. Analysis of the GS polypeptide composition by immunoblotting revealed two different polypeptides. A and B, with a molecular mass of 42 and 40 kDa, respectively. In the scutellum subunit A was already present in the ungerminated seed and remained unchanged, whereas subunit B appeared on day 2 and increased about 5‐fold during germination. Polypeptide B also appeared later during germination in the aleurone layer, roots and weakly in the etiolated shoots. By immunogold microscopy, GS was detected in the scutellum and the aleurone layer of barley seeds during germination. Subcellular localization of GS on ultrathin cryosections showed that a cytosolic isozyme was present in the scutellum. Our study confirms that only a cytosolic GS is expressed in barley seed, and its subunit composition changes during germination.