© 1988 Heron Publishing—Victoria, Canada
Adaptations to intermittent drying in germinating Eucalyptus sieberi L. Johnson seeds and young seedlings
A. Gibson and E. P. Bachelard
Department of Forestry, Australian National University, GPO Box 4, Canberra, ACT 2601, Australia / Received February 29, 1988
Summary
Before Eucalyptus sieberi L. Johnson seeds germinate, the protein reserves in a small group of cells in the collet are mobilized and the cells swell
sufficiently to break the seed coat allowing further water uptake. If the seedling is desiccated at this stage, the embryo
remains viable and when the seed is rewetted reserves are mobilized in the cells immediately behind those which expanded initially.
Mobilization of reserves and subsequent cell elongation occur sequentially along the hypocotyl after successive dry periods
until the reserves are exhausted. Early in the sequence, the distal end of the hypocotyl extends and is positively geotropic,
whereas at the end of the sequence the proximal end of the hypocotyl extends and is negatively geotropic, raising the cotyledons
rapidly. If the radicle is destroyed or unable to elongate, it is replaced by two adventitious roots, one below the petiole
of each cotyledon. Indole acetic acid and sucrose can substitute for the cotyledons in the production of adventitious roots.
