Developmental and Structural Section
Yin, Xiaofeng , Meicenheimer, Roger .
A Quantitative Analysis of Discontinuous Phyllotactic Transition in Diphasiastrum digitatum.
The overall goal of the current study was to quantitatively characterize underlying events at the level of the shoot apical meristem (SAM), associated with discontinuous phyllotactic transitions, in order to assess the validity of existing phyllotactic model predictions of these changes in aspecies producing microphylls as opposed to megaphylls. Phyllotaxis is devoted to the description,characterization, and generation of the patterns made by repeating elements in plants. During the ontogeny of many plants, phyllotactic patterns undergo transitions. These can be characterized as continuous or discontinuous. In continuous transitions, the order of pattern changes within the same phyllotactic series [e.g., within the Fibonnaci series from a 1(2, 3) patternto a 1(3, 5) pattern]. In discontinuous transitions, the pattern undergoes transition from one series to another [e.g.,from Fibonacci series 1(1,1,2,3...) to Lucas series 1(1,3,4,7...)] or from one jugacity level to another [e.g., from decussate 2(1,1) to tricussate 3(1,1)]. Although there is a high prevalence of discontinuous transitions in nature, most theoretical and empirical studies of phyllotaxis have been focused on characterization of Fibonacci spiral patterns and only a few have considered discontinuous transitions. In Diphasiastrum digitatum (Lycopodiaceae), the rhizome gives rise to vertical aerial vegetative shoots, which in turn give rise to flattened vegetative branches. During the third and/or fourth year, some of the flattened vegetative branches become radially symmetric and undergo transformation into groups of four reproductive shoots (strobili) by apical dichotomies. Discontinuous transitionsoccur in association with stroboli formation in D. digitatum. Scanning electron microscopy was used to study the phyllotaxis at the level of the shoot apical meristems during these transitions. Image J was used to quantify divergence angle, plastochron ratio, leaf insertion angle, diameter, circumference, and transverse area of the SAM, van Iterson's parameter b, and displacement angle of the SAM. Results indicated that in D. digitatum, discontinuous transitions occurred at two particular times: 1. Decussate pattern of vegetative branches transition to a spiral pattern during formation of reproductive SAM's. 2. The (3, 5) spiral pattern of microphylls on the proximal portion of the strobili transition to a tricussate pattern of sporophylls on the distal portion of the strobili. Empircally determined parameters were used to assess the validity of predicted changes by several theoretical models of phyllotaxis during these discontinuous transitions.
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1 - Miami University, Botany, 501 E High St, Oxford, OH, 45056, USA
2 - Miami University, Department Of Botany, DEPT OF BOTANY, MIAMI UNIV, Oxford, OH, 45056, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Union D/Hyatt
Date: Tuesday, July 10th, 2012
Time: 10:45 AM