Epicormic Bud Development inQuercus roburL. Studies of Endogenous IAA, ABA, IAA Polar Transport and Water Potential in Cambial Tissues10

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Abstract
Seasonal measurements of IAA,3 made using GC-MS, 4 indicated that in Q. robur the spring initiation of cambial activity and onset of visible bud outgrowth in the canopy is preceded by an increase in cambial region IAA. The effects of notch-girdles cut into the bole indicated that IAA in the cambial region later was present in separate physiological pools, with only the polar-transported fraction affecting epicormic bud outgrowth. The stage in the spring when the epicormic buds grew out coincided with an increase both in cambial region IAA and in the capacity of cambial explants for IAA polar transport. Thus the stimulus needed by the epicormic buds to overcome inhibition by polar-transported IAA appeared to be self-generated. The observed effects of exogenous hormones on epicormic bud outgrowth from stem explants indicated that this stimulus might be cytokinin. The seasonal changes detected in cambial region ABA3 were consistent with a role for stress-induced ABA in the induction of epicormic bud dormancy after canopy development during the summer. No consistent effects of stand thinning on cambial region IAA, ABA, water potentials or water contents were detected, although polar transport of exogenous IAA by cambial region explants removed in the spring was reduced by thinning.