Apple leaf senescence: leaf disc compared to attached leaf.

Attached apple leaves (Pyrus malus L., Golden Delicious) began to lose protein in early August as the first sign of senescence. Apple leaf discs prepared from samples before early August gained protein for up to 7 days after detachment. After early August, the loss of protein from leaf discs was no greater than the loss from attached leaves in 7 days. The loss of chlorophyll from leaf discs began over 2 months before attached leaves began to lose chlorophyll naturally and before leaf discs lost protein. Leaf discs from presenescent leaves did not senesce significantly faster when maintained in darkness instead of 12 hours of light. In general, the loss of protein and chlorophyll from apple leaf discs after 7 days was much less than for most other leaf types studied.