TISSUE-SPECIFIC DISTRIBUTION OF GLUTAMINE-SYNTHETASE IN POTATO-TUBERS

Cytosolic isoforms of the enzyme glutamine synthetase (GS) located in the phloem have been implicated in the mobilization of nitrogen for in tracellular transport in higher plants. The potato tuber represents an important reservoir of nitrogen and an approach was made to the chara cterization of GS in this organ, particularly at the stages of sprouti ng and of new tuber formation. By immunoblotting after SDS-PAGE, and b y immunological tissue printing, it was possible to conclude that a cy tosolic GS is present in tubers and sprouts, and that it is mainly exp ressed in the internal phloem, in a very precise tissue-specific patte rn of distribution. These data provide additional clues to the interpr etation of the functional role of GS in the mobilization of nitrogen a nd its utilization in growing parts of the plant. The importance of mo rphological data and localization studies in complementing molecular a nd biochemical work is emphasized. The proposed functional importance of the internal phloem in Solanum tuberosum organs is also reinforced. (C) 1996 Annals of Botany Company