Lamina Abortion in Terminal Bud-Scale Leaves of Populus deltoides during Dormancy Induction

Abstract

Bud scales of terminal buds of Populus deltoides Bartr. ex Marsh. are formed by enlarged stipules. The laminae of the first bud-scale leaves mature and abscise, but the lamina of the last bud-scale leaf (or leaves) senesces prematurely and aborts. The immature lamina of the aborting leaf turns black, shrivels, and protrudes from the bud scales until physically dislodged during bud break the following spring. Senescence of the aborting bud-scale lamina begins with loss of starch and enlargement and vacuolation of cells abaxial to the dorsal bundle of the midrib at the lamina tip. These processes progress basipetally and laterally in the lamina, with degeneration becoming particularly evident in the spongy mesophyll. While lamina degeneration is under way, an abscission meristem begins to form distal to the stipules at the petiole base. Cell divisions initiating the abscission meristem are first evident in the reactivated adaxial meristem, and they spread laterally and obliquely across the petiole base. The...