Developmental and Structural Section
Christianson, Michael L. , Jernstedt, Judy .
Vegetatively-branched short-shoots in Ginkgo biloba.
Notwithstanding obvious morphological differences between the long-shoots and the short-shoots of Ginkgo biloba, the anatomical similarity of their apical meristems and the ability of an axis to switch from long-shoot to short-shoot (and back again) are clear indicators that these two growth forms are fundamentally identical. We have recently described additional morphological differences in the short-shoots borne on fertile trees. In addition to the well-known differences in micro- and mega-sporangia and the axillary structures which bear them, analysis of distributions of these lateral structures along short-shoots reveals differences in both location (the boundary between bracts and foliage leaves vs the 5th bract back from that boundary) and pattern by which numbers of reproductive lateral shoots increase (symmetrical vs basipetally-biased) on mega- and micro-sporangiate trees, respectively. — Rare cases of laterally-branched short-shoots can be found and show that short-shoots are able to make indeterminate (vegetative) lateral shoots as well as the usual determinate (reproductive) laterals. Comparison of the positions where such "vegetative” shoots arise vs. the positions where reproductive structures arise could reveal how a general potential to form axillary meristems in the ancestral-short-shoot of Ginkgo became restricted and localized during evolution, resulting in the distinctive short-shoots of micro- and mega-sporangiate trees. The two examples seen both had 3 lateral short-shoots of approximately the same age at or near the seemingly aborted tip of the mother short-shoot. This location and the ca. 137.5Âº divergence of these laterals around the main short-shoot axis suggest that damage to the apex of the main axis could cause the branching. Ablation of the apical meristem of shoot-shoots would test this hypothesis and might allow us to generate the large numbers of branched short shoots we would like to examine. This work was supported in part by the Grady L. Webster Memorial Research Fund.
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1 - University of California, Davis, Plant Sciences, Mail Stop 1, One Shields Avenue, Davis, CA, 95616
2 - University of California, Davis, Plant Sciences, One Shields Avenue, Davis, California, 95616-8780, USA
Presentation Type: Oral Paper:Papers for BSA Sections
Location: Ballroom 3/Cliff Lodge - Level B
Date: Monday, July 27th, 2009
Time: 4:45 PM