Molecular cloning of Glutamine Synthetase cDNA from Lactuca sativa: Sequence analysis and gene expression during storage

In order to understand the factors contributing to postharvest deterioration of lettuce, the changes in ammonia content as well as activity and gene expression of GS were investigated in the outer and inner leaves of lettuce head during storage at 20°C. About two times higher ammonia content out of its initial content was found in the outer leaf portion after the end of 96 h storage period. GS activity in this portion declined to about 27% of the initial level by 24 h of storage, while activity in the inner leaf portion almost unchanged throughout the storage. To understand clearly these biochemical changes, a cDNA encoding GS was isolated. cloned and sequenced from lettuce leaves. The partial cDNA clone referred to as LsGS (Lactuca saliva Glutamine Synthetase; AB440673) consisted of 799 nucleotides which showed more than 80% similarity for both nucleotide and amino acid level with the GS genes of other dicotyledonous plant. Northern blot analysis showed that the level of transcript of GS decreased in the outer-leaf portion after 24 h of storage which well correlates with the enzyme activity of this portion. Although, we found no specific trend in GS activity in the inner-leaf portion, the transcript level gradually increased until the end of storage period. The inconsistency between enzyme activity and gene expression may suggest that GS expression in lettuce is controlled by multiple levels of regulations in a tissue-specific manner. © 2009 Asian Network for Scientific Information.