2. Materials and methods
2.1. Lettuce stem discs and storage
Commercially grown and harvested crisp-head iceberg lettuce
(Lactuca sativa L.) were purchased froma local retailer and stored at
1.5 C. About 3000 stems were cored from the lettuce head. After
removing the top and bottom portion of each stem, the middle
portion was cut into discs with 2 mm thickness (about 2 g) each
according to Tom as-Barber an, Gil, Casta~ ner, Art es, and Saltveit
(1997). About 5e7 discs were obtained from each stem.