Cloning and expression of γ-glutamyl transpeptidase and its relationship to greening in crushed garlic (Allium sativum) cloves

BACKGROUND: Garlic greening occurs when garlic cloves are stored at low temperature, increasing 1-propenyl cysteine sulfoxide, which is induced by ?-glutamyl transpeptidase (GGT) activity. Although the metabolism of the ?-glutamyl peptide is important for the biosynthesis of green pigments in crushed garlic cloves, garlic GGT is poorly characterised. RESULTS: For the analysis of GGT at the gene level, the garlic GGT sequence was partially cloned using an onion GGT sequence. The relationship between garlic greening and related gene expressions, depending on storage condition, was investigated using reverse transcription polymerase chain reaction for garlic GGT and alliinase. Three storage conditions were set: A, storage at a constant temperature of 20 degrees C; B, storage at 20 degrees C for 3 months and then transfer to 0. C for an additional 3 months; C, storage at 0 degrees C for 3 months and then transfer to 20 degrees C for an additional 3 months. GGT expression increased under storage condition B and decreased under storage condition C. However, alliinase expression was not affected by storage condition. CONCLUSION: Greening in crushed garlic cloves increases with increasing GGT expression at low temperature, while alliinase expression is not affected. (C) 2011 Society of Chemical Industry